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Index: docs/PCHInternals.rst | |
=================================================================== | |
--- docs/PCHInternals.rst (revision 0) | |
+++ docs/PCHInternals.rst (working copy) | |
@@ -0,0 +1,573 @@ | |
+======================================== | |
+Precompiled Header and Modules Internals | |
+======================================== | |
+ | |
+.. contents:: | |
+ :local: | |
+ | |
+This document describes the design and implementation of Clang's precompiled | |
+headers (PCH) and modules. If you are interested in the end-user view, please | |
+see the `User's Manual <UsersManual.html#precompiledheaders>`_. | |
+ | |
+Using Precompiled Headers with ``clang`` | |
+---------------------------------------- | |
+ | |
+The Clang compiler frontend, ``clang -cc1``, supports two command line options | |
+for generating and using PCH files. | |
+ | |
+To generate PCH files using ``clang -cc1``, use the option :option:`-emit-pch`: | |
+ | |
+.. code-block:: bash | |
+ | |
+ $ clang -cc1 test.h -emit-pch -o test.h.pch | |
+ | |
+This option is transparently used by ``clang`` when generating PCH files. The | |
+resulting PCH file contains the serialized form of the compiler's internal | |
+representation after it has completed parsing and semantic analysis. The PCH | |
+file can then be used as a prefix header with the :option:`-include-pch` | |
+option: | |
+ | |
+.. code-block:: bash | |
+ | |
+ $ clang -cc1 -include-pch test.h.pch test.c -o test.s | |
+ | |
+Design Philosophy | |
+----------------- | |
+ | |
+Precompiled headers are meant to improve overall compile times for projects, so | |
+the design of precompiled headers is entirely driven by performance concerns. | |
+The use case for precompiled headers is relatively simple: when there is a | |
+common set of headers that is included in nearly every source file in the | |
+project, we *precompile* that bundle of headers into a single precompiled | |
+header (PCH file). Then, when compiling the source files in the project, we | |
+load the PCH file first (as a prefix header), which acts as a stand-in for that | |
+bundle of headers. | |
+ | |
+A precompiled header implementation improves performance when: | |
+ | |
+* Loading the PCH file is significantly faster than re-parsing the bundle of | |
+ headers stored within the PCH file. Thus, a precompiled header design | |
+ attempts to minimize the cost of reading the PCH file. Ideally, this cost | |
+ should not vary with the size of the precompiled header file. | |
+ | |
+* The cost of generating the PCH file initially is not so large that it | |
+ counters the per-source-file performance improvement due to eliminating the | |
+ need to parse the bundled headers in the first place. This is particularly | |
+ important on multi-core systems, because PCH file generation serializes the | |
+ build when all compilations require the PCH file to be up-to-date. | |
+ | |
+Modules, as implemented in Clang, use the same mechanisms as precompiled | |
+headers to save a serialized AST file (one per module) and use those AST | |
+modules. From an implementation standpoint, modules are a generalization of | |
+precompiled headers, lifting a number of restrictions placed on precompiled | |
+headers. In particular, there can only be one precompiled header and it must | |
+be included at the beginning of the translation unit. The extensions to the | |
+AST file format required for modules are discussed in the section on | |
+:ref:`modules <pchinternals-modules>`. | |
+ | |
+Clang's AST files are designed with a compact on-disk representation, which | |
+minimizes both creation time and the time required to initially load the AST | |
+file. The AST file itself contains a serialized representation of Clang's | |
+abstract syntax trees and supporting data structures, stored using the same | |
+compressed bitstream as `LLVM's bitcode file format | |
+<http://llvm.org/docs/BitCodeFormat.html>`_. | |
+ | |
+Clang's AST files are loaded "lazily" from disk. When an AST file is initially | |
+loaded, Clang reads only a small amount of data from the AST file to establish | |
+where certain important data structures are stored. The amount of data read in | |
+this initial load is independent of the size of the AST file, such that a | |
+larger AST file does not lead to longer AST load times. The actual header data | |
+in the AST file --- macros, functions, variables, types, etc. --- is loaded | |
+only when it is referenced from the user's code, at which point only that | |
+entity (and those entities it depends on) are deserialized from the AST file. | |
+With this approach, the cost of using an AST file for a translation unit is | |
+proportional to the amount of code actually used from the AST file, rather than | |
+being proportional to the size of the AST file itself. | |
+ | |
+When given the :option:`-print-stats` option, Clang produces statistics | |
+describing how much of the AST file was actually loaded from disk. For a | |
+simple "Hello, World!" program that includes the Apple ``Cocoa.h`` header | |
+(which is built as a precompiled header), this option illustrates how little of | |
+the actual precompiled header is required: | |
+ | |
+.. code-block:: none | |
+ | |
+ *** PCH Statistics: | |
+ 933 stat cache hits | |
+ 4 stat cache misses | |
+ 895/39981 source location entries read (2.238563%) | |
+ 19/15315 types read (0.124061%) | |
+ 20/82685 declarations read (0.024188%) | |
+ 154/58070 identifiers read (0.265197%) | |
+ 0/7260 selectors read (0.000000%) | |
+ 0/30842 statements read (0.000000%) | |
+ 4/8400 macros read (0.047619%) | |
+ 1/4995 lexical declcontexts read (0.020020%) | |
+ 0/4413 visible declcontexts read (0.000000%) | |
+ 0/7230 method pool entries read (0.000000%) | |
+ 0 method pool misses | |
+ | |
+For this small program, only a tiny fraction of the source locations, types, | |
+declarations, identifiers, and macros were actually deserialized from the | |
+precompiled header. These statistics can be useful to determine whether the | |
+AST file implementation can be improved by making more of the implementation | |
+lazy. | |
+ | |
+Precompiled headers can be chained. When you create a PCH while including an | |
+existing PCH, Clang can create the new PCH by referencing the original file and | |
+only writing the new data to the new file. For example, you could create a PCH | |
+out of all the headers that are very commonly used throughout your project, and | |
+then create a PCH for every single source file in the project that includes the | |
+code that is specific to that file, so that recompiling the file itself is very | |
+fast, without duplicating the data from the common headers for every file. The | |
+mechanisms behind chained precompiled headers are discussed in a :ref:`later | |
+section <pchinternals-chained>`. | |
+ | |
+AST File Contents | |
+----------------- | |
+ | |
+Clang's AST files are organized into several different blocks, each of which | |
+contains the serialized representation of a part of Clang's internal | |
+representation. Each of the blocks corresponds to either a block or a record | |
+within `LLVM's bitstream format <http://llvm.org/docs/BitCodeFormat.html>`_. | |
+The contents of each of these logical blocks are described below. | |
+ | |
+.. image:: PCHLayout1.png | |
+ | |
+For a given AST file, the `llvm-bcanalyzer | |
+<http://llvm.org/docs/CommandGuide/llvm-bcanalyzer.html>`_ utility can be used | |
+to examine the actual structure of the bitstream for the AST file. This | |
+information can be used both to help understand the structure of the AST file | |
+and to isolate areas where AST files can still be optimized, e.g., through the | |
+introduction of abbreviations. | |
+ | |
+Metadata Block | |
+^^^^^^^^^^^^^^ | |
+ | |
+The metadata block contains several records that provide information about how | |
+the AST file was built. This metadata is primarily used to validate the use of | |
+an AST file. For example, a precompiled header built for a 32-bit x86 target | |
+cannot be used when compiling for a 64-bit x86 target. The metadata block | |
+contains information about: | |
+ | |
+Language options | |
+ Describes the particular language dialect used to compile the AST file, | |
+ including major options (e.g., Objective-C support) and more minor options | |
+ (e.g., support for "``//``" comments). The contents of this record correspond to | |
+ the ``LangOptions`` class. | |
+ | |
+Target architecture | |
+ The target triple that describes the architecture, platform, and ABI for | |
+ which the AST file was generated, e.g., ``i386-apple-darwin9``. | |
+ | |
+AST version | |
+ The major and minor version numbers of the AST file format. Changes in the | |
+ minor version number should not affect backward compatibility, while changes | |
+ in the major version number imply that a newer compiler cannot read an older | |
+ precompiled header (and vice-versa). | |
+ | |
+Original file name | |
+ The full path of the header that was used to generate the AST file. | |
+ | |
+Predefines buffer | |
+ Although not explicitly stored as part of the metadata, the predefines buffer | |
+ is used in the validation of the AST file. The predefines buffer itself | |
+ contains code generated by the compiler to initialize the preprocessor state | |
+ according to the current target, platform, and command-line options. For | |
+ example, the predefines buffer will contain "``#define __STDC__ 1``" when we | |
+ are compiling C without Microsoft extensions. The predefines buffer itself | |
+ is stored within the :ref:`pchinternals-sourcemgr`, but its contents are | |
+ verified along with the rest of the metadata. | |
+ | |
+A chained PCH file (that is, one that references another PCH) and a module | |
+(which may import other modules) have additional metadata containing the list | |
+of all AST files that this AST file depends on. Each of those files will be | |
+loaded along with this AST file. | |
+ | |
+For chained precompiled headers, the language options, target architecture and | |
+predefines buffer data is taken from the end of the chain, since they have to | |
+match anyway. | |
+ | |
+.. _pchinternals-sourcemgr: | |
+ | |
+Source Manager Block | |
+^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+The source manager block contains the serialized representation of Clang's | |
+`SourceManager <InternalsManual.html#SourceLocation>`_ class, which handles the | |
+mapping from source locations (as represented in Clang's abstract syntax tree) | |
+into actual column/line positions within a source file or macro instantiation. | |
+The AST file's representation of the source manager also includes information | |
+about all of the headers that were (transitively) included when building the | |
+AST file. | |
+ | |
+The bulk of the source manager block is dedicated to information about the | |
+various files, buffers, and macro instantiations into which a source location | |
+can refer. Each of these is referenced by a numeric "file ID", which is a | |
+unique number (allocated starting at 1) stored in the source location. Clang | |
+serializes the information for each kind of file ID, along with an index that | |
+maps file IDs to the position within the AST file where the information about | |
+that file ID is stored. The data associated with a file ID is loaded only when | |
+required by the front end, e.g., to emit a diagnostic that includes a macro | |
+instantiation history inside the header itself. | |
+ | |
+The source manager block also contains information about all of the headers | |
+that were included when building the AST file. This includes information about | |
+the controlling macro for the header (e.g., when the preprocessor identified | |
+that the contents of the header dependent on a macro like | |
+``LLVM_CLANG_SOURCEMANAGER_H``) along with a cached version of the results of | |
+the ``stat()`` system calls performed when building the AST file. The latter | |
+is particularly useful in reducing system time when searching for include | |
+files. | |
+ | |
+.. _pchinternals-preprocessor: | |
+ | |
+Preprocessor Block | |
+^^^^^^^^^^^^^^^^^^ | |
+ | |
+The preprocessor block contains the serialized representation of the | |
+preprocessor. Specifically, it contains all of the macros that have been | |
+defined by the end of the header used to build the AST file, along with the | |
+token sequences that comprise each macro. The macro definitions are only read | |
+from the AST file when the name of the macro first occurs in the program. This | |
+lazy loading of macro definitions is triggered by lookups into the | |
+:ref:`identifier table <pchinternals-ident-table>`. | |
+ | |
+.. _pchinternals-types: | |
+ | |
+Types Block | |
+^^^^^^^^^^^ | |
+ | |
+The types block contains the serialized representation of all of the types | |
+referenced in the translation unit. Each Clang type node (``PointerType``, | |
+``FunctionProtoType``, etc.) has a corresponding record type in the AST file. | |
+When types are deserialized from the AST file, the data within the record is | |
+used to reconstruct the appropriate type node using the AST context. | |
+ | |
+Each type has a unique type ID, which is an integer that uniquely identifies | |
+that type. Type ID 0 represents the NULL type, type IDs less than | |
+``NUM_PREDEF_TYPE_IDS`` represent predefined types (``void``, ``float``, etc.), | |
+while other "user-defined" type IDs are assigned consecutively from | |
+``NUM_PREDEF_TYPE_IDS`` upward as the types are encountered. The AST file has | |
+an associated mapping from the user-defined types block to the location within | |
+the types block where the serialized representation of that type resides, | |
+enabling lazy deserialization of types. When a type is referenced from within | |
+the AST file, that reference is encoded using the type ID shifted left by 3 | |
+bits. The lower three bits are used to represent the ``const``, ``volatile``, | |
+and ``restrict`` qualifiers, as in Clang's | |
+`QualType <http://clang.llvm.org/docs/InternalsManual.html#Type>`_ class. | |
+ | |
+.. _pchinternals-decls: | |
+ | |
+Declarations Block | |
+^^^^^^^^^^^^^^^^^^ | |
+ | |
+The declarations block contains the serialized representation of all of the | |
+declarations referenced in the translation unit. Each Clang declaration node | |
+(``VarDecl``, ``FunctionDecl``, etc.) has a corresponding record type in the | |
+AST file. When declarations are deserialized from the AST file, the data | |
+within the record is used to build and populate a new instance of the | |
+corresponding ``Decl`` node. As with types, each declaration node has a | |
+numeric ID that is used to refer to that declaration within the AST file. In | |
+addition, a lookup table provides a mapping from that numeric ID to the offset | |
+within the precompiled header where that declaration is described. | |
+ | |
+Declarations in Clang's abstract syntax trees are stored hierarchically. At | |
+the top of the hierarchy is the translation unit (``TranslationUnitDecl``), | |
+which contains all of the declarations in the translation unit but is not | |
+actually written as a specific declaration node. Its child declarations (such | |
+as functions or struct types) may also contain other declarations inside them, | |
+and so on. Within Clang, each declaration is stored within a `declaration | |
+context <http://clang.llvm.org/docs/InternalsManual.html#DeclContext>`_, as | |
+represented by the ``DeclContext`` class. Declaration contexts provide the | |
+mechanism to perform name lookup within a given declaration (e.g., find the | |
+member named ``x`` in a structure) and iterate over the declarations stored | |
+within a context (e.g., iterate over all of the fields of a structure for | |
+structure layout). | |
+ | |
+In Clang's AST file format, deserializing a declaration that is a | |
+``DeclContext`` is a separate operation from deserializing all of the | |
+declarations stored within that declaration context. Therefore, Clang will | |
+deserialize the translation unit declaration without deserializing the | |
+declarations within that translation unit. When required, the declarations | |
+stored within a declaration context will be deserialized. There are two | |
+representations of the declarations within a declaration context, which | |
+correspond to the name-lookup and iteration behavior described above: | |
+ | |
+* When the front end performs name lookup to find a name ``x`` within a given | |
+ declaration context (for example, during semantic analysis of the expression | |
+ ``p->x``, where ``p``'s type is defined in the precompiled header), Clang | |
+ refers to an on-disk hash table that maps from the names within that | |
+ declaration context to the declaration IDs that represent each visible | |
+ declaration with that name. The actual declarations will then be | |
+ deserialized to provide the results of name lookup. | |
+* When the front end performs iteration over all of the declarations within a | |
+ declaration context, all of those declarations are immediately | |
+ de-serialized. For large declaration contexts (e.g., the translation unit), | |
+ this operation is expensive; however, large declaration contexts are not | |
+ traversed in normal compilation, since such a traversal is unnecessary. | |
+ However, it is common for the code generator and semantic analysis to | |
+ traverse declaration contexts for structs, classes, unions, and | |
+ enumerations, although those contexts contain relatively few declarations in | |
+ the common case. | |
+ | |
+Statements and Expressions | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Statements and expressions are stored in the AST file in both the :ref:`types | |
+<pchinternals-types>` and the :ref:`declarations <pchinternals-decls>` blocks, | |
+because every statement or expression will be associated with either a type or | |
+declaration. The actual statement and expression records are stored | |
+immediately following the declaration or type that owns the statement or | |
+expression. For example, the statement representing the body of a function | |
+will be stored directly following the declaration of the function. | |
+ | |
+As with types and declarations, each statement and expression kind in Clang's | |
+abstract syntax tree (``ForStmt``, ``CallExpr``, etc.) has a corresponding | |
+record type in the AST file, which contains the serialized representation of | |
+that statement or expression. Each substatement or subexpression within an | |
+expression is stored as a separate record (which keeps most records to a fixed | |
+size). Within the AST file, the subexpressions of an expression are stored, in | |
+reverse order, prior to the expression that owns those expression, using a form | |
+of `Reverse Polish Notation | |
+<http://en.wikipedia.org/wiki/Reverse_Polish_notation>`_. For example, an | |
+expression ``3 - 4 + 5`` would be represented as follows: | |
+ | |
++-----------------------+ | |
+| ``IntegerLiteral(5)`` | | |
++-----------------------+ | |
+| ``IntegerLiteral(4)`` | | |
++-----------------------+ | |
+| ``IntegerLiteral(3)`` | | |
++-----------------------+ | |
+| ``IntegerLiteral(-)`` | | |
++-----------------------+ | |
+| ``IntegerLiteral(+)`` | | |
++-----------------------+ | |
+| ``STOP`` | | |
++-----------------------+ | |
+ | |
+When reading this representation, Clang evaluates each expression record it | |
+encounters, builds the appropriate abstract syntax tree node, and then pushes | |
+that expression on to a stack. When a record contains *N* subexpressions --- | |
+``BinaryOperator`` has two of them --- those expressions are popped from the | |
+top of the stack. The special STOP code indicates that we have reached the end | |
+of a serialized expression or statement; other expression or statement records | |
+may follow, but they are part of a different expression. | |
+ | |
+.. _pchinternals-ident-table: | |
+ | |
+Identifier Table Block | |
+^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+The identifier table block contains an on-disk hash table that maps each | |
+identifier mentioned within the AST file to the serialized representation of | |
+the identifier's information (e.g, the ``IdentifierInfo`` structure). The | |
+serialized representation contains: | |
+ | |
+* The actual identifier string. | |
+* Flags that describe whether this identifier is the name of a built-in, a | |
+ poisoned identifier, an extension token, or a macro. | |
+* If the identifier names a macro, the offset of the macro definition within | |
+ the :ref:`pchinternals-preprocessor`. | |
+* If the identifier names one or more declarations visible from translation | |
+ unit scope, the :ref:`declaration IDs <pchinternals-decls>` of these | |
+ declarations. | |
+ | |
+When an AST file is loaded, the AST file reader mechanism introduces itself | |
+into the identifier table as an external lookup source. Thus, when the user | |
+program refers to an identifier that has not yet been seen, Clang will perform | |
+a lookup into the identifier table. If an identifier is found, its contents | |
+(macro definitions, flags, top-level declarations, etc.) will be deserialized, | |
+at which point the corresponding ``IdentifierInfo`` structure will have the | |
+same contents it would have after parsing the headers in the AST file. | |
+ | |
+Within the AST file, the identifiers used to name declarations are represented | |
+with an integral value. A separate table provides a mapping from this integral | |
+value (the identifier ID) to the location within the on-disk hash table where | |
+that identifier is stored. This mapping is used when deserializing the name of | |
+a declaration, the identifier of a token, or any other construct in the AST | |
+file that refers to a name. | |
+ | |
+.. _pchinternals-method-pool: | |
+ | |
+Method Pool Block | |
+^^^^^^^^^^^^^^^^^ | |
+ | |
+The method pool block is represented as an on-disk hash table that serves two | |
+purposes: it provides a mapping from the names of Objective-C selectors to the | |
+set of Objective-C instance and class methods that have that particular | |
+selector (which is required for semantic analysis in Objective-C) and also | |
+stores all of the selectors used by entities within the AST file. The design | |
+of the method pool is similar to that of the :ref:`identifier table | |
+<pchinternals-ident-table>`: the first time a particular selector is formed | |
+during the compilation of the program, Clang will search in the on-disk hash | |
+table of selectors; if found, Clang will read the Objective-C methods | |
+associated with that selector into the appropriate front-end data structure | |
+(``Sema::InstanceMethodPool`` and ``Sema::FactoryMethodPool`` for instance and | |
+class methods, respectively). | |
+ | |
+As with identifiers, selectors are represented by numeric values within the AST | |
+file. A separate index maps these numeric selector values to the offset of the | |
+selector within the on-disk hash table, and will be used when de-serializing an | |
+Objective-C method declaration (or other Objective-C construct) that refers to | |
+the selector. | |
+ | |
+AST Reader Integration Points | |
+----------------------------- | |
+ | |
+The "lazy" deserialization behavior of AST files requires their integration | |
+into several completely different submodules of Clang. For example, lazily | |
+deserializing the declarations during name lookup requires that the name-lookup | |
+routines be able to query the AST file to find entities stored there. | |
+ | |
+For each Clang data structure that requires direct interaction with the AST | |
+reader logic, there is an abstract class that provides the interface between | |
+the two modules. The ``ASTReader`` class, which handles the loading of an AST | |
+file, inherits from all of these abstract classes to provide lazy | |
+deserialization of Clang's data structures. ``ASTReader`` implements the | |
+following abstract classes: | |
+ | |
+``StatSysCallCache`` | |
+ This abstract interface is associated with the ``FileManager`` class, and is | |
+ used whenever the file manager is going to perform a ``stat()`` system call. | |
+ | |
+``ExternalSLocEntrySource`` | |
+ This abstract interface is associated with the ``SourceManager`` class, and | |
+ is used whenever the :ref:`source manager <pchinternals-sourcemgr>` needs to | |
+ load the details of a file, buffer, or macro instantiation. | |
+ | |
+``IdentifierInfoLookup`` | |
+ This abstract interface is associated with the ``IdentifierTable`` class, and | |
+ is used whenever the program source refers to an identifier that has not yet | |
+ been seen. In this case, the AST reader searches for this identifier within | |
+ its :ref:`identifier table <pchinternals-ident-table>` to load any top-level | |
+ declarations or macros associated with that identifier. | |
+ | |
+``ExternalASTSource`` | |
+ This abstract interface is associated with the ``ASTContext`` class, and is | |
+ used whenever the abstract syntax tree nodes need to loaded from the AST | |
+ file. It provides the ability to de-serialize declarations and types | |
+ identified by their numeric values, read the bodies of functions when | |
+ required, and read the declarations stored within a declaration context | |
+ (either for iteration or for name lookup). | |
+ | |
+``ExternalSemaSource`` | |
+ This abstract interface is associated with the ``Sema`` class, and is used | |
+ whenever semantic analysis needs to read information from the :ref:`global | |
+ method pool <pchinternals-method-pool>`. | |
+ | |
+.. _pchinternals-chained: | |
+ | |
+Chained precompiled headers | |
+--------------------------- | |
+ | |
+Chained precompiled headers were initially intended to improve the performance | |
+of IDE-centric operations such as syntax highlighting and code completion while | |
+a particular source file is being edited by the user. To minimize the amount | |
+of reparsing required after a change to the file, a form of precompiled header | |
+--- called a precompiled *preamble* --- is automatically generated by parsing | |
+all of the headers in the source file, up to and including the last | |
+``#include``. When only the source file changes (and none of the headers it | |
+depends on), reparsing of that source file can use the precompiled preamble and | |
+start parsing after the ``#include``\ s, so parsing time is proportional to the | |
+size of the source file (rather than all of its includes). However, the | |
+compilation of that translation unit may already use a precompiled header: in | |
+this case, Clang will create the precompiled preamble as a chained precompiled | |
+header that refers to the original precompiled header. This drastically | |
+reduces the time needed to serialize the precompiled preamble for use in | |
+reparsing. | |
+ | |
+Chained precompiled headers get their name because each precompiled header can | |
+depend on one other precompiled header, forming a chain of dependencies. A | |
+translation unit will then include the precompiled header that starts the chain | |
+(i.e., nothing depends on it). This linearity of dependencies is important for | |
+the semantic model of chained precompiled headers, because the most-recent | |
+precompiled header can provide information that overrides the information | |
+provided by the precompiled headers it depends on, just like a header file | |
+``B.h`` that includes another header ``A.h`` can modify the state produced by | |
+parsing ``A.h``, e.g., by ``#undef``'ing a macro defined in ``A.h``. | |
+ | |
+There are several ways in which chained precompiled headers generalize the AST | |
+file model: | |
+ | |
+Numbering of IDs | |
+ Many different kinds of entities --- identifiers, declarations, types, etc. | |
+ --- have ID numbers that start at 1 or some other predefined constant and | |
+ grow upward. Each precompiled header records the maximum ID number it has | |
+ assigned in each category. Then, when a new precompiled header is generated | |
+ that depends on (chains to) another precompiled header, it will start | |
+ counting at the next available ID number. This way, one can determine, given | |
+ an ID number, which AST file actually contains the entity. | |
+ | |
+Name lookup | |
+ When writing a chained precompiled header, Clang attempts to write only | |
+ information that has changed from the precompiled header on which it is | |
+ based. This changes the lookup algorithm for the various tables, such as the | |
+ :ref:`identifier table <pchinternals-ident-table>`: the search starts at the | |
+ most-recent precompiled header. If no entry is found, lookup then proceeds | |
+ to the identifier table in the precompiled header it depends on, and so one. | |
+ Once a lookup succeeds, that result is considered definitive, overriding any | |
+ results from earlier precompiled headers. | |
+ | |
+Update records | |
+ There are various ways in which a later precompiled header can modify the | |
+ entities described in an earlier precompiled header. For example, later | |
+ precompiled headers can add entries into the various name-lookup tables for | |
+ the translation unit or namespaces, or add new categories to an Objective-C | |
+ class. Each of these updates is captured in an "update record" that is | |
+ stored in the chained precompiled header file and will be loaded along with | |
+ the original entity. | |
+ | |
+.. _pchinternals-modules: | |
+ | |
+Modules | |
+------- | |
+ | |
+Modules generalize the chained precompiled header model yet further, from a | |
+linear chain of precompiled headers to an arbitrary directed acyclic graph | |
+(DAG) of AST files. All of the same techniques used to make chained | |
+precompiled headers work --- ID number, name lookup, update records --- are | |
+shared with modules. However, the DAG nature of modules introduce a number of | |
+additional complications to the model: | |
+ | |
+Numbering of IDs | |
+ The simple, linear numbering scheme used in chained precompiled headers falls | |
+ apart with the module DAG, because different modules may end up with | |
+ different numbering schemes for entities they imported from common shared | |
+ modules. To account for this, each module file provides information about | |
+ which modules it depends on and which ID numbers it assigned to the entities | |
+ in those modules, as well as which ID numbers it took for its own new | |
+ entities. The AST reader then maps these "local" ID numbers into a "global" | |
+ ID number space for the current translation unit, providing a 1-1 mapping | |
+ between entities (in whatever AST file they inhabit) and global ID numbers. | |
+ If that translation unit is then serialized into an AST file, this mapping | |
+ will be stored for use when the AST file is imported. | |
+ | |
+Declaration merging | |
+ It is possible for a given entity (from the language's perspective) to be | |
+ declared multiple times in different places. For example, two different | |
+ headers can have the declaration of ``printf`` or could forward-declare | |
+ ``struct stat``. If each of those headers is included in a module, and some | |
+ third party imports both of those modules, there is a potentially serious | |
+ problem: name lookup for ``printf`` or ``struct stat`` will find both | |
+ declarations, but the AST nodes are unrelated. This would result in a | |
+ compilation error, due to an ambiguity in name lookup. Therefore, the AST | |
+ reader performs declaration merging according to the appropriate language | |
+ semantics, ensuring that the two disjoint declarations are merged into a | |
+ single redeclaration chain (with a common canonical declaration), so that it | |
+ is as if one of the headers had been included before the other. | |
+ | |
+Name Visibility | |
+ Modules allow certain names that occur during module creation to be "hidden", | |
+ so that they are not part of the public interface of the module and are not | |
+ visible to its clients. The AST reader maintains a "visible" bit on various | |
+ AST nodes (declarations, macros, etc.) to indicate whether that particular | |
+ AST node is currently visible; the various name lookup mechanisms in Clang | |
+ inspect the visible bit to determine whether that entity, which is still in | |
+ the AST (because other, visible AST nodes may depend on it), can actually be | |
+ found by name lookup. When a new (sub)module is imported, it may make | |
+ existing, non-visible, already-deserialized AST nodes visible; it is the | |
+ responsibility of the AST reader to find and update these AST nodes when it | |
+ is notified of the import. | |
+ | |
Index: docs/ThreadSanitizer.html | |
=================================================================== | |
--- docs/ThreadSanitizer.html (revision 169710) | |
+++ docs/ThreadSanitizer.html (working copy) | |
@@ -1,126 +0,0 @@ | |
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" | |
- "http://www.w3.org/TR/html4/strict.dtd"> | |
-<!-- Material used from: HTML 4.01 specs: http://www.w3.org/TR/html401/ --> | |
-<html> | |
-<head> | |
- <META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> | |
- <title>ThreadSanitizer, a race detector</title> | |
- <link type="text/css" rel="stylesheet" href="../menu.css"> | |
- <link type="text/css" rel="stylesheet" href="../content.css"> | |
- <style type="text/css"> | |
- td { | |
- vertical-align: top; | |
- } | |
- </style> | |
-</head> | |
-<body> | |
- | |
-<!--#include virtual="../menu.html.incl"--> | |
- | |
-<div id="content"> | |
- | |
-<h1>ThreadSanitizer</h1> | |
-<ul> | |
- <li> <a href="#intro">Introduction</a> | |
- <li> <a href="#howtobuild">How to Build</a> | |
- <li> <a href="#platforms">Supported Platforms</a> | |
- <li> <a href="#usage">Usage</a> | |
- <li> <a href="#limitations">Limitations</a> | |
- <li> <a href="#status">Current Status</a> | |
- <li> <a href="#moreinfo">More Information</a> | |
-</ul> | |
- | |
-<h2 id="intro">Introduction</h2> | |
-ThreadSanitizer is a tool that detects data races. <BR> | |
-It consists of a compiler instrumentation module and a run-time library. <BR> | |
-Typical slowdown introduced by ThreadSanitizer is <b>5x-15x</b> (TODO: these numbers are | |
-approximate so far). | |
- | |
-<h2 id="howtobuild">How to build</h2> | |
-Follow the <a href="../get_started.html">clang build instructions</a>. | |
-CMake build is supported.<BR> | |
- | |
-<h2 id="platforms">Supported Platforms</h2> | |
-ThreadSanitizer is supported on Linux x86_64 (tested on Ubuntu 10.04). <BR> | |
-Support for MacOS 10.7 (64-bit only) is planned for late 2012. <BR> | |
-Support for 32-bit platforms is problematic and not yet planned. | |
- | |
- | |
- | |
-<h2 id="usage">Usage</h2> | |
-Simply compile your program with <tt>-fsanitize=thread -fPIE</tt> and link it | |
-with <tt>-fsanitize=thread -pie</tt>.<BR> | |
-To get a reasonable performance add <tt>-O1</tt> or higher. <BR> | |
-Use <tt>-g</tt> to get file names and line numbers in the warning messages. <BR> | |
- | |
-Example: | |
-<pre> | |
-% cat projects/compiler-rt/lib/tsan/output_tests/tiny_race.c | |
-#include <pthread.h> | |
-int Global; | |
-void *Thread1(void *x) { | |
- Global = 42; | |
- return x; | |
-} | |
-int main() { | |
- pthread_t t; | |
- pthread_create(&t, NULL, Thread1, NULL); | |
- Global = 43; | |
- pthread_join(t, NULL); | |
- return Global; | |
-} | |
-</pre> | |
- | |
-<pre> | |
-% clang -fsanitize=thread -g -O1 tiny_race.c -fPIE -pie | |
-</pre> | |
- | |
-If a bug is detected, the program will print an error message to stderr. | |
-Currently, ThreadSanitizer symbolizes its output using an external | |
-<tt>addr2line</tt> | |
-process (this will be fixed in future). | |
-<pre> | |
-% TSAN_OPTIONS=strip_path_prefix=`pwd`/ # Don't print full paths. | |
-% ./a.out 2> log | |
-% cat log | |
-WARNING: ThreadSanitizer: data race (pid=19219) | |
- Write of size 4 at 0x7fcf47b21bc0 by thread 1: | |
- #0 Thread1 tiny_race.c:4 (exe+0x00000000a360) | |
- Previous write of size 4 at 0x7fcf47b21bc0 by main thread: | |
- #0 main tiny_race.c:10 (exe+0x00000000a3b4) | |
- Thread 1 (running) created at: | |
- #0 pthread_create ??:0 (exe+0x00000000c790) | |
- #1 main tiny_race.c:9 (exe+0x00000000a3a4) | |
-</pre> | |
- | |
- | |
-<h2 id="limitations">Limitations</h2> | |
-<ul> | |
-<li> ThreadSanitizer uses more real memory than a native run. | |
-At the default settings the memory overhead is 9x plus 9Mb per each thread. | |
-Settings with 5x and 3x overhead (but less accurate analysis) are also available. | |
-<li> ThreadSanitizer maps (but does not reserve) a lot of virtual address space. | |
-This means that tools like <tt>ulimit</tt> may not work as usually expected. | |
-<li> Static linking is not supported. | |
-<li> ThreadSanitizer requires <tt>-fPIE -pie</tt> | |
-</ul> | |
- | |
- | |
-<h2 id="status">Current Status</h2> | |
-ThreadSanitizer is in alpha stage. | |
-It is known to work on large C++ programs using pthreads, but we do not promise | |
-anything (yet). <BR> | |
-C++11 threading is not yet supported. <BR> | |
-The test suite is integrated into CMake build and can be run with | |
-<tt>make check-tsan</tt> command. <BR> | |
- | |
-We are actively working on enhancing the tool -- stay tuned. | |
-Any help, especially in the form of minimized standalone tests is more than welcome. | |
- | |
-<h2 id="moreinfo">More Information</h2> | |
-<a href="http://code.google.com/p/thread-sanitizer/">http://code.google.com/p/thread-sanitizer</a>. | |
- | |
- | |
-</div> | |
-</body> | |
-</html> | |
Index: docs/PCHInternals.html | |
=================================================================== | |
--- docs/PCHInternals.html (revision 169710) | |
+++ docs/PCHInternals.html (working copy) | |
@@ -1,658 +0,0 @@ | |
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" | |
- "http://www.w3.org/TR/html4/strict.dtd"> | |
-<html> | |
-<head> | |
- <title>Precompiled Header and Modules Internals</title> | |
- <link type="text/css" rel="stylesheet" href="../menu.css"> | |
- <link type="text/css" rel="stylesheet" href="../content.css"> | |
- <style type="text/css"> | |
- td { | |
- vertical-align: top; | |
- } | |
- </style> | |
-</head> | |
- | |
-<body> | |
- | |
-<!--#include virtual="../menu.html.incl"--> | |
- | |
-<div id="content"> | |
- | |
-<h1>Precompiled Header and Modules Internals</h1> | |
- | |
- <p>This document describes the design and implementation of Clang's | |
- precompiled headers (PCH) and modules. If you are interested in the end-user | |
- view, please see the <a | |
- href="UsersManual.html#precompiledheaders">User's Manual</a>.</p> | |
- | |
- <p><b>Table of Contents</b></p> | |
- <ul> | |
- <li><a href="#usage">Using Precompiled Headers with | |
- <tt>clang</tt></a></li> | |
- <li><a href="#philosophy">Design Philosophy</a></li> | |
- <li><a href="#contents">Serialized AST File Contents</a> | |
- <ul> | |
- <li><a href="#metadata">Metadata Block</a></li> | |
- <li><a href="#sourcemgr">Source Manager Block</a></li> | |
- <li><a href="#preprocessor">Preprocessor Block</a></li> | |
- <li><a href="#types">Types Block</a></li> | |
- <li><a href="#decls">Declarations Block</a></li> | |
- <li><a href="#stmt">Statements and Expressions</a></li> | |
- <li><a href="#idtable">Identifier Table Block</a></li> | |
- <li><a href="#method-pool">Method Pool Block</a></li> | |
- </ul> | |
- </li> | |
- <li><a href="#tendrils">AST Reader Integration Points</a></li> | |
- <li><a href="#chained">Chained precompiled headers</a></li> | |
- <li><a href="#modules">Modules</a></li> | |
-</ul> | |
- | |
-<h2 id="usage">Using Precompiled Headers with <tt>clang</tt></h2> | |
- | |
-<p>The Clang compiler frontend, <tt>clang -cc1</tt>, supports two command line | |
-options for generating and using PCH files.<p> | |
- | |
-<p>To generate PCH files using <tt>clang -cc1</tt>, use the option | |
-<b><tt>-emit-pch</tt></b>: | |
- | |
-<pre> $ clang -cc1 test.h -emit-pch -o test.h.pch </pre> | |
- | |
-<p>This option is transparently used by <tt>clang</tt> when generating | |
-PCH files. The resulting PCH file contains the serialized form of the | |
-compiler's internal representation after it has completed parsing and | |
-semantic analysis. The PCH file can then be used as a prefix header | |
-with the <b><tt>-include-pch</tt></b> option:</p> | |
- | |
-<pre> | |
- $ clang -cc1 -include-pch test.h.pch test.c -o test.s | |
-</pre> | |
- | |
-<h2 id="philosophy">Design Philosophy</h2> | |
- | |
-<p>Precompiled headers are meant to improve overall compile times for | |
- projects, so the design of precompiled headers is entirely driven by | |
- performance concerns. The use case for precompiled headers is | |
- relatively simple: when there is a common set of headers that is | |
- included in nearly every source file in the project, we | |
- <i>precompile</i> that bundle of headers into a single precompiled | |
- header (PCH file). Then, when compiling the source files in the | |
- project, we load the PCH file first (as a prefix header), which acts | |
- as a stand-in for that bundle of headers.</p> | |
- | |
-<p>A precompiled header implementation improves performance when:</p> | |
-<ul> | |
- <li>Loading the PCH file is significantly faster than re-parsing the | |
- bundle of headers stored within the PCH file. Thus, a precompiled | |
- header design attempts to minimize the cost of reading the PCH | |
- file. Ideally, this cost should not vary with the size of the | |
- precompiled header file.</li> | |
- | |
- <li>The cost of generating the PCH file initially is not so large | |
- that it counters the per-source-file performance improvement due to | |
- eliminating the need to parse the bundled headers in the first | |
- place. This is particularly important on multi-core systems, because | |
- PCH file generation serializes the build when all compilations | |
- require the PCH file to be up-to-date.</li> | |
-</ul> | |
- | |
-<p>Modules, as implemented in Clang, use the same mechanisms as | |
-precompiled headers to save a serialized AST file (one per module) and | |
-use those AST modules. From an implementation standpoint, modules are | |
-a generalization of precompiled headers, lifting a number of | |
-restrictions placed on precompiled headers. In particular, there can | |
-only be one precompiled header and it must be included at the | |
-beginning of the translation unit. The extensions to the AST file | |
-format required for modules are discussed in the section on <a href="#modules">modules</a>.</p> | |
- | |
-<p>Clang's AST files are designed with a compact on-disk | |
-representation, which minimizes both creation time and the time | |
-required to initially load the AST file. The AST file itself contains | |
-a serialized representation of Clang's abstract syntax trees and | |
-supporting data structures, stored using the same compressed bitstream | |
-as <a href="http://llvm.org/docs/BitCodeFormat.html">LLVM's bitcode | |
-file format</a>.</p> | |
- | |
-<p>Clang's AST files are loaded "lazily" from disk. When an | |
-AST file is initially loaded, Clang reads only a small amount of data | |
-from the AST file to establish where certain important data structures | |
-are stored. The amount of data read in this initial load is | |
-independent of the size of the AST file, such that a larger AST file | |
-does not lead to longer AST load times. The actual header data in the | |
-AST file--macros, functions, variables, types, etc.--is loaded only | |
-when it is referenced from the user's code, at which point only that | |
-entity (and those entities it depends on) are deserialized from the | |
-AST file. With this approach, the cost of using an AST file | |
-for a translation unit is proportional to the amount of code actually | |
-used from the AST file, rather than being proportional to the size of | |
-the AST file itself.</p> | |
- | |
-<p>When given the <code>-print-stats</code> option, Clang produces | |
-statistics describing how much of the AST file was actually | |
-loaded from disk. For a simple "Hello, World!" program that includes | |
-the Apple <code>Cocoa.h</code> header (which is built as a precompiled | |
-header), this option illustrates how little of the actual precompiled | |
-header is required:</p> | |
- | |
-<pre> | |
-*** PCH Statistics: | |
- 933 stat cache hits | |
- 4 stat cache misses | |
- 895/39981 source location entries read (2.238563%) | |
- 19/15315 types read (0.124061%) | |
- 20/82685 declarations read (0.024188%) | |
- 154/58070 identifiers read (0.265197%) | |
- 0/7260 selectors read (0.000000%) | |
- 0/30842 statements read (0.000000%) | |
- 4/8400 macros read (0.047619%) | |
- 1/4995 lexical declcontexts read (0.020020%) | |
- 0/4413 visible declcontexts read (0.000000%) | |
- 0/7230 method pool entries read (0.000000%) | |
- 0 method pool misses | |
-</pre> | |
- | |
-<p>For this small program, only a tiny fraction of the source | |
-locations, types, declarations, identifiers, and macros were actually | |
-deserialized from the precompiled header. These statistics can be | |
-useful to determine whether the AST file implementation can | |
-be improved by making more of the implementation lazy.</p> | |
- | |
-<p>Precompiled headers can be chained. When you create a PCH while | |
-including an existing PCH, Clang can create the new PCH by referencing | |
-the original file and only writing the new data to the new file. For | |
-example, you could create a PCH out of all the headers that are very | |
-commonly used throughout your project, and then create a PCH for every | |
-single source file in the project that includes the code that is | |
-specific to that file, so that recompiling the file itself is very fast, | |
-without duplicating the data from the common headers for every | |
-file. The mechanisms behind chained precompiled headers are discussed | |
-in a <a href="#chained">later section</a>. | |
- | |
-<h2 id="contents">AST File Contents</h2> | |
- | |
-<img src="PCHLayout.png" style="float:right" alt="Precompiled header layout"> | |
- | |
-<p>Clang's AST files are organized into several different | |
-blocks, each of which contains the serialized representation of a part | |
-of Clang's internal representation. Each of the blocks corresponds to | |
-either a block or a record within <a | |
- href="http://llvm.org/docs/BitCodeFormat.html">LLVM's bitstream | |
-format</a>. The contents of each of these logical blocks are described | |
-below.</p> | |
- | |
-<p>For a given AST file, the <a | |
-href="http://llvm.org/cmds/llvm-bcanalyzer.html"><code>llvm-bcanalyzer</code></a> | |
-utility can be used to examine the actual structure of the bitstream | |
-for the AST file. This information can be used both to help | |
-understand the structure of the AST file and to isolate | |
-areas where AST files can still be optimized, e.g., through | |
-the introduction of abbreviations.</p> | |
- | |
-<h3 id="metadata">Metadata Block</h3> | |
- | |
-<p>The metadata block contains several records that provide | |
-information about how the AST file was built. This metadata | |
-is primarily used to validate the use of an AST file. For | |
-example, a precompiled header built for a 32-bit x86 target cannot be used | |
-when compiling for a 64-bit x86 target. The metadata block contains | |
-information about:</p> | |
- | |
-<dl> | |
- <dt>Language options</dt> | |
- <dd>Describes the particular language dialect used to compile the | |
-AST file, including major options (e.g., Objective-C support) and more | |
-minor options (e.g., support for "//" comments). The contents of this | |
-record correspond to the <code>LangOptions</code> class.</dd> | |
- | |
- <dt>Target architecture</dt> | |
- <dd>The target triple that describes the architecture, platform, and | |
-ABI for which the AST file was generated, e.g., | |
-<code>i386-apple-darwin9</code>.</dd> | |
- | |
- <dt>AST version</dt> | |
- <dd>The major and minor version numbers of the AST file | |
-format. Changes in the minor version number should not affect backward | |
-compatibility, while changes in the major version number imply that a | |
-newer compiler cannot read an older precompiled header (and | |
-vice-versa).</dd> | |
- | |
- <dt>Original file name</dt> | |
- <dd>The full path of the header that was used to generate the | |
-AST file.</dd> | |
- | |
- <dt>Predefines buffer</dt> | |
- <dd>Although not explicitly stored as part of the metadata, the | |
-predefines buffer is used in the validation of the AST file. | |
-The predefines buffer itself contains code generated by the compiler | |
-to initialize the preprocessor state according to the current target, | |
-platform, and command-line options. For example, the predefines buffer | |
-will contain "<code>#define __STDC__ 1</code>" when we are compiling C | |
-without Microsoft extensions. The predefines buffer itself is stored | |
-within the <a href="#sourcemgr">source manager block</a>, but its | |
-contents are verified along with the rest of the metadata.</dd> | |
- | |
-</dl> | |
- | |
-<p>A chained PCH file (that is, one that references another PCH) and a | |
-module (which may import other modules) have additional metadata | |
-containing the list of all AST files that this AST file depends | |
-on. Each of those files will be loaded along with this AST file.</p> | |
- | |
-<p>For chained precompiled headers, the language options, target | |
-architecture and predefines buffer data is taken from the end of the | |
-chain, since they have to match anyway.</p> | |
- | |
-<h3 id="sourcemgr">Source Manager Block</h3> | |
- | |
-<p>The source manager block contains the serialized representation of | |
-Clang's <a | |
- href="InternalsManual.html#SourceLocation">SourceManager</a> class, | |
-which handles the mapping from source locations (as represented in | |
-Clang's abstract syntax tree) into actual column/line positions within | |
-a source file or macro instantiation. The AST file's | |
-representation of the source manager also includes information about | |
-all of the headers that were (transitively) included when building the | |
-AST file.</p> | |
- | |
-<p>The bulk of the source manager block is dedicated to information | |
-about the various files, buffers, and macro instantiations into which | |
-a source location can refer. Each of these is referenced by a numeric | |
-"file ID", which is a unique number (allocated starting at 1) stored | |
-in the source location. Clang serializes the information for each kind | |
-of file ID, along with an index that maps file IDs to the position | |
-within the AST file where the information about that file ID is | |
-stored. The data associated with a file ID is loaded only when | |
-required by the front end, e.g., to emit a diagnostic that includes a | |
-macro instantiation history inside the header itself.</p> | |
- | |
-<p>The source manager block also contains information about all of the | |
-headers that were included when building the AST file. This | |
-includes information about the controlling macro for the header (e.g., | |
-when the preprocessor identified that the contents of the header | |
-dependent on a macro like <code>LLVM_CLANG_SOURCEMANAGER_H</code>) | |
-along with a cached version of the results of the <code>stat()</code> | |
-system calls performed when building the AST file. The | |
-latter is particularly useful in reducing system time when searching | |
-for include files.</p> | |
- | |
-<h3 id="preprocessor">Preprocessor Block</h3> | |
- | |
-<p>The preprocessor block contains the serialized representation of | |
-the preprocessor. Specifically, it contains all of the macros that | |
-have been defined by the end of the header used to build the | |
-AST file, along with the token sequences that comprise each | |
-macro. The macro definitions are only read from the AST file when the | |
-name of the macro first occurs in the program. This lazy loading of | |
-macro definitions is triggered by lookups into the <a | |
- href="#idtable">identifier table</a>.</p> | |
- | |
-<h3 id="types">Types Block</h3> | |
- | |
-<p>The types block contains the serialized representation of all of | |
-the types referenced in the translation unit. Each Clang type node | |
-(<code>PointerType</code>, <code>FunctionProtoType</code>, etc.) has a | |
-corresponding record type in the AST file. When types are deserialized | |
-from the AST file, the data within the record is used to | |
-reconstruct the appropriate type node using the AST context.</p> | |
- | |
-<p>Each type has a unique type ID, which is an integer that uniquely | |
-identifies that type. Type ID 0 represents the NULL type, type IDs | |
-less than <code>NUM_PREDEF_TYPE_IDS</code> represent predefined types | |
-(<code>void</code>, <code>float</code>, etc.), while other | |
-"user-defined" type IDs are assigned consecutively from | |
-<code>NUM_PREDEF_TYPE_IDS</code> upward as the types are encountered. | |
-The AST file has an associated mapping from the user-defined types | |
-block to the location within the types block where the serialized | |
-representation of that type resides, enabling lazy deserialization of | |
-types. When a type is referenced from within the AST file, that | |
-reference is encoded using the type ID shifted left by 3 bits. The | |
-lower three bits are used to represent the <code>const</code>, | |
-<code>volatile</code>, and <code>restrict</code> qualifiers, as in | |
-Clang's <a | |
- href="http://clang.llvm.org/docs/InternalsManual.html#Type">QualType</a> | |
-class.</p> | |
- | |
-<h3 id="decls">Declarations Block</h3> | |
- | |
-<p>The declarations block contains the serialized representation of | |
-all of the declarations referenced in the translation unit. Each Clang | |
-declaration node (<code>VarDecl</code>, <code>FunctionDecl</code>, | |
-etc.) has a corresponding record type in the AST file. When | |
-declarations are deserialized from the AST file, the data | |
-within the record is used to build and populate a new instance of the | |
-corresponding <code>Decl</code> node. As with types, each declaration | |
-node has a numeric ID that is used to refer to that declaration within | |
-the AST file. In addition, a lookup table provides a mapping from that | |
-numeric ID to the offset within the precompiled header where that | |
-declaration is described.</p> | |
- | |
-<p>Declarations in Clang's abstract syntax trees are stored | |
-hierarchically. At the top of the hierarchy is the translation unit | |
-(<code>TranslationUnitDecl</code>), which contains all of the | |
-declarations in the translation unit but is not actually written as a | |
-specific declaration node. Its child declarations (such as | |
-functions or struct types) may also contain other declarations inside | |
-them, and so on. Within Clang, each declaration is stored within a <a | |
-href="http://clang.llvm.org/docs/InternalsManual.html#DeclContext">declaration | |
-context</a>, as represented by the <code>DeclContext</code> class. | |
-Declaration contexts provide the mechanism to perform name lookup | |
-within a given declaration (e.g., find the member named <code>x</code> | |
-in a structure) and iterate over the declarations stored within a | |
-context (e.g., iterate over all of the fields of a structure for | |
-structure layout).</p> | |
- | |
-<p>In Clang's AST file format, deserializing a declaration | |
-that is a <code>DeclContext</code> is a separate operation from | |
-deserializing all of the declarations stored within that declaration | |
-context. Therefore, Clang will deserialize the translation unit | |
-declaration without deserializing the declarations within that | |
-translation unit. When required, the declarations stored within a | |
-declaration context will be deserialized. There are two representations | |
-of the declarations within a declaration context, which correspond to | |
-the name-lookup and iteration behavior described above:</p> | |
- | |
-<ul> | |
- <li>When the front end performs name lookup to find a name | |
- <code>x</code> within a given declaration context (for example, | |
- during semantic analysis of the expression <code>p->x</code>, | |
- where <code>p</code>'s type is defined in the precompiled header), | |
- Clang refers to an on-disk hash table that maps from the names | |
- within that declaration context to the declaration IDs that | |
- represent each visible declaration with that name. The actual | |
- declarations will then be deserialized to provide the results of | |
- name lookup.</li> | |
- | |
- <li>When the front end performs iteration over all of the | |
- declarations within a declaration context, all of those declarations | |
- are immediately de-serialized. For large declaration contexts (e.g., | |
- the translation unit), this operation is expensive; however, large | |
- declaration contexts are not traversed in normal compilation, since | |
- such a traversal is unnecessary. However, it is common for the code | |
- generator and semantic analysis to traverse declaration contexts for | |
- structs, classes, unions, and enumerations, although those contexts | |
- contain relatively few declarations in the common case.</li> | |
-</ul> | |
- | |
-<h3 id="stmt">Statements and Expressions</h3> | |
- | |
-<p>Statements and expressions are stored in the AST file in | |
-both the <a href="#types">types</a> and the <a | |
- href="#decls">declarations</a> blocks, because every statement or | |
-expression will be associated with either a type or declaration. The | |
-actual statement and expression records are stored immediately | |
-following the declaration or type that owns the statement or | |
-expression. For example, the statement representing the body of a | |
-function will be stored directly following the declaration of the | |
-function.</p> | |
- | |
-<p>As with types and declarations, each statement and expression kind | |
-in Clang's abstract syntax tree (<code>ForStmt</code>, | |
-<code>CallExpr</code>, etc.) has a corresponding record type in the | |
-AST file, which contains the serialized representation of | |
-that statement or expression. Each substatement or subexpression | |
-within an expression is stored as a separate record (which keeps most | |
-records to a fixed size). Within the AST file, the | |
-subexpressions of an expression are stored, in reverse order, prior to the expression | |
-that owns those expression, using a form of <a | |
-href="http://en.wikipedia.org/wiki/Reverse_Polish_notation">Reverse | |
-Polish Notation</a>. For example, an expression <code>3 - 4 + 5</code> | |
-would be represented as follows:</p> | |
- | |
-<table border="1"> | |
- <tr><td><code>IntegerLiteral(5)</code></td></tr> | |
- <tr><td><code>IntegerLiteral(4)</code></td></tr> | |
- <tr><td><code>IntegerLiteral(3)</code></td></tr> | |
- <tr><td><code>BinaryOperator(-)</code></td></tr> | |
- <tr><td><code>BinaryOperator(+)</code></td></tr> | |
- <tr><td>STOP</td></tr> | |
-</table> | |
- | |
-<p>When reading this representation, Clang evaluates each expression | |
-record it encounters, builds the appropriate abstract syntax tree node, | |
-and then pushes that expression on to a stack. When a record contains <i>N</i> | |
-subexpressions--<code>BinaryOperator</code> has two of them--those | |
-expressions are popped from the top of the stack. The special STOP | |
-code indicates that we have reached the end of a serialized expression | |
-or statement; other expression or statement records may follow, but | |
-they are part of a different expression.</p> | |
- | |
-<h3 id="idtable">Identifier Table Block</h3> | |
- | |
-<p>The identifier table block contains an on-disk hash table that maps | |
-each identifier mentioned within the AST file to the | |
-serialized representation of the identifier's information (e.g, the | |
-<code>IdentifierInfo</code> structure). The serialized representation | |
-contains:</p> | |
- | |
-<ul> | |
- <li>The actual identifier string.</li> | |
- <li>Flags that describe whether this identifier is the name of a | |
- built-in, a poisoned identifier, an extension token, or a | |
- macro.</li> | |
- <li>If the identifier names a macro, the offset of the macro | |
- definition within the <a href="#preprocessor">preprocessor | |
- block</a>.</li> | |
- <li>If the identifier names one or more declarations visible from | |
- translation unit scope, the <a href="#decls">declaration IDs</a> of these | |
- declarations.</li> | |
-</ul> | |
- | |
-<p>When an AST file is loaded, the AST file reader | |
-mechanism introduces itself into the identifier table as an external | |
-lookup source. Thus, when the user program refers to an identifier | |
-that has not yet been seen, Clang will perform a lookup into the | |
-identifier table. If an identifier is found, its contents (macro | |
-definitions, flags, top-level declarations, etc.) will be | |
-deserialized, at which point the corresponding | |
-<code>IdentifierInfo</code> structure will have the same contents it | |
-would have after parsing the headers in the AST file.</p> | |
- | |
-<p>Within the AST file, the identifiers used to name declarations are represented with an integral value. A separate table provides a mapping from this integral value (the identifier ID) to the location within the on-disk | |
-hash table where that identifier is stored. This mapping is used when | |
-deserializing the name of a declaration, the identifier of a token, or | |
-any other construct in the AST file that refers to a name.</p> | |
- | |
-<h3 id="method-pool">Method Pool Block</h3> | |
- | |
-<p>The method pool block is represented as an on-disk hash table that | |
-serves two purposes: it provides a mapping from the names of | |
-Objective-C selectors to the set of Objective-C instance and class | |
-methods that have that particular selector (which is required for | |
-semantic analysis in Objective-C) and also stores all of the selectors | |
-used by entities within the AST file. The design of the | |
-method pool is similar to that of the <a href="#idtable">identifier | |
-table</a>: the first time a particular selector is formed during the | |
-compilation of the program, Clang will search in the on-disk hash | |
-table of selectors; if found, Clang will read the Objective-C methods | |
-associated with that selector into the appropriate front-end data | |
-structure (<code>Sema::InstanceMethodPool</code> and | |
-<code>Sema::FactoryMethodPool</code> for instance and class methods, | |
-respectively).</p> | |
- | |
-<p>As with identifiers, selectors are represented by numeric values | |
-within the AST file. A separate index maps these numeric selector | |
-values to the offset of the selector within the on-disk hash table, | |
-and will be used when de-serializing an Objective-C method declaration | |
-(or other Objective-C construct) that refers to the selector.</p> | |
- | |
-<h2 id="tendrils">AST Reader Integration Points</h2> | |
- | |
-<p>The "lazy" deserialization behavior of AST files requires | |
-their integration into several completely different submodules of | |
-Clang. For example, lazily deserializing the declarations during name | |
-lookup requires that the name-lookup routines be able to query the | |
-AST file to find entities stored there.</p> | |
- | |
-<p>For each Clang data structure that requires direct interaction with | |
-the AST reader logic, there is an abstract class that provides | |
-the interface between the two modules. The <code>ASTReader</code> | |
-class, which handles the loading of an AST file, inherits | |
-from all of these abstract classes to provide lazy deserialization of | |
-Clang's data structures. <code>ASTReader</code> implements the | |
-following abstract classes:</p> | |
- | |
-<dl> | |
- <dt><code>StatSysCallCache</code></dt> | |
- <dd>This abstract interface is associated with the | |
- <code>FileManager</code> class, and is used whenever the file | |
- manager is going to perform a <code>stat()</code> system call.</dd> | |
- | |
- <dt><code>ExternalSLocEntrySource</code></dt> | |
- <dd>This abstract interface is associated with the | |
- <code>SourceManager</code> class, and is used whenever the | |
- <a href="#sourcemgr">source manager</a> needs to load the details | |
- of a file, buffer, or macro instantiation.</dd> | |
- | |
- <dt><code>IdentifierInfoLookup</code></dt> | |
- <dd>This abstract interface is associated with the | |
- <code>IdentifierTable</code> class, and is used whenever the | |
- program source refers to an identifier that has not yet been seen. | |
- In this case, the AST reader searches for | |
- this identifier within its <a href="#idtable">identifier table</a> | |
- to load any top-level declarations or macros associated with that | |
- identifier.</dd> | |
- | |
- <dt><code>ExternalASTSource</code></dt> | |
- <dd>This abstract interface is associated with the | |
- <code>ASTContext</code> class, and is used whenever the abstract | |
- syntax tree nodes need to loaded from the AST file. It | |
- provides the ability to de-serialize declarations and types | |
- identified by their numeric values, read the bodies of functions | |
- when required, and read the declarations stored within a | |
- declaration context (either for iteration or for name lookup).</dd> | |
- | |
- <dt><code>ExternalSemaSource</code></dt> | |
- <dd>This abstract interface is associated with the <code>Sema</code> | |
- class, and is used whenever semantic analysis needs to read | |
- information from the <a href="#methodpool">global method | |
- pool</a>.</dd> | |
-</dl> | |
- | |
-<h2 id="chained">Chained precompiled headers</h2> | |
- | |
-<p>Chained precompiled headers were initially intended to improve the | |
-performance of IDE-centric operations such as syntax highlighting and | |
-code completion while a particular source file is being edited by the | |
-user. To minimize the amount of reparsing required after a change to | |
-the file, a form of precompiled header--called a precompiled | |
-<i>preamble</i>--is automatically generated by parsing all of the | |
-headers in the source file, up to and including the last | |
-#include. When only the source file changes (and none of the headers | |
-it depends on), reparsing of that source file can use the precompiled | |
-preamble and start parsing after the #includes, so parsing time is | |
-proportional to the size of the source file (rather than all of its | |
-includes). However, the compilation of that translation unit | |
-may already use a precompiled header: in this case, Clang will create | |
-the precompiled preamble as a chained precompiled header that refers | |
-to the original precompiled header. This drastically reduces the time | |
-needed to serialize the precompiled preamble for use in reparsing.</p> | |
- | |
-<p>Chained precompiled headers get their name because each precompiled header | |
-can depend on one other precompiled header, forming a chain of | |
-dependencies. A translation unit will then include the precompiled | |
-header that starts the chain (i.e., nothing depends on it). This | |
-linearity of dependencies is important for the semantic model of | |
-chained precompiled headers, because the most-recent precompiled | |
-header can provide information that overrides the information provided | |
-by the precompiled headers it depends on, just like a header file | |
-<code>B.h</code> that includes another header <code>A.h</code> can | |
-modify the state produced by parsing <code>A.h</code>, e.g., by | |
-<code>#undef</code>'ing a macro defined in <code>A.h</code>.</p> | |
- | |
-<p>There are several ways in which chained precompiled headers | |
-generalize the AST file model:</p> | |
- | |
-<dl> | |
- <dt>Numbering of IDs</dt> | |
- <dd>Many different kinds of entities--identifiers, declarations, | |
- types, etc.---have ID numbers that start at 1 or some other | |
- predefined constant and grow upward. Each precompiled header records | |
- the maximum ID number it has assigned in each category. Then, when a | |
- new precompiled header is generated that depends on (chains to) | |
- another precompiled header, it will start counting at the next | |
- available ID number. This way, one can determine, given an ID | |
- number, which AST file actually contains the entity.</dd> | |
- | |
- <dt>Name lookup</dt> | |
- <dd>When writing a chained precompiled header, Clang attempts to | |
- write only information that has changed from the precompiled header | |
- on which it is based. This changes the lookup algorithm for the | |
- various tables, such as the <a href="#idtable">identifier table</a>: | |
- the search starts at the most-recent precompiled header. If no entry | |
- is found, lookup then proceeds to the identifier table in the | |
- precompiled header it depends on, and so one. Once a lookup | |
- succeeds, that result is considered definitive, overriding any | |
- results from earlier precompiled headers.</dd> | |
- | |
- <dt>Update records</dt> | |
- <dd>There are various ways in which a later precompiled header can | |
- modify the entities described in an earlier precompiled header. For | |
- example, later precompiled headers can add entries into the various | |
- name-lookup tables for the translation unit or namespaces, or add | |
- new categories to an Objective-C class. Each of these updates is | |
- captured in an "update record" that is stored in the chained | |
- precompiled header file and will be loaded along with the original | |
- entity.</dd> | |
-</dl> | |
- | |
-<h2 id="modules">Modules</h2> | |
- | |
-<p>Modules generalize the chained precompiled header model yet | |
-further, from a linear chain of precompiled headers to an arbitrary | |
-directed acyclic graph (DAG) of AST files. All of the same techniques | |
-used to make chained precompiled headers work---ID number, name | |
-lookup, update records---are shared with modules. However, the DAG | |
-nature of modules introduce a number of additional complications to | |
-the model: | |
- | |
-<dl> | |
- <dt>Numbering of IDs</dt> | |
- <dd>The simple, linear numbering scheme used in chained precompiled | |
- headers falls apart with the module DAG, because different modules | |
- may end up with different numbering schemes for entities they | |
- imported from common shared modules. To account for this, each | |
- module file provides information about which modules it depends on | |
- and which ID numbers it assigned to the entities in those modules, | |
- as well as which ID numbers it took for its own new entities. The | |
- AST reader then maps these "local" ID numbers into a "global" ID | |
- number space for the current translation unit, providing a 1-1 | |
- mapping between entities (in whatever AST file they inhabit) and | |
- global ID numbers. If that translation unit is then serialized into | |
- an AST file, this mapping will be stored for use when the AST file | |
- is imported.</dd> | |
- | |
- <dt>Declaration merging</dt> | |
- <dd>It is possible for a given entity (from the language's | |
- perspective) to be declared multiple times in different places. For | |
- example, two different headers can have the declaration of | |
- <tt>printf</tt> or could forward-declare <tt>struct stat</tt>. If | |
- each of those headers is included in a module, and some third party | |
- imports both of those modules, there is a potentially serious | |
- problem: name lookup for <tt>printf</tt> or <tt>struct stat</tt> will | |
- find both declarations, but the AST nodes are unrelated. This would | |
- result in a compilation error, due to an ambiguity in name | |
- lookup. Therefore, the AST reader performs declaration merging | |
- according to the appropriate language semantics, ensuring that the | |
- two disjoint declarations are merged into a single redeclaration | |
- chain (with a common canonical declaration), so that it is as if one | |
- of the headers had been included before the other.</dd> | |
- | |
- <dt>Name Visibility</dt> | |
- <dd>Modules allow certain names that occur during module creation to | |
- be "hidden", so that they are not part of the public interface of | |
- the module and are not visible to its clients. The AST reader | |
- maintains a "visible" bit on various AST nodes (declarations, macros, | |
- etc.) to indicate whether that particular AST node is currently | |
- visible; the various name lookup mechanisms in Clang inspect the | |
- visible bit to determine whether that entity, which is still in the | |
- AST (because other, visible AST nodes may depend on it), can | |
- actually be found by name lookup. When a new (sub)module is | |
- imported, it may make existing, non-visible, already-deserialized | |
- AST nodes visible; it is the responsibility of the AST reader to | |
- find and update these AST nodes when it is notified of the import.</dd> | |
- | |
-</dl> | |
- | |
-</div> | |
- | |
-</body> | |
-</html> | |
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- | |
-<h1>Clang Language Extensions</h1> | |
- | |
-<ul> | |
-<li><a href="#intro">Introduction</a></li> | |
-<li><a href="#feature_check">Feature Checking Macros</a></li> | |
-<li><a href="#has_include">Include File Checking Macros</a></li> | |
-<li><a href="#builtinmacros">Builtin Macros</a></li> | |
-<li><a href="#vectors">Vectors and Extended Vectors</a></li> | |
-<li><a href="#deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> attributes</a></li> | |
-<li><a href="#attributes-on-enumerators">Attributes on enumerators</a></li> | |
-<li><a href="#user_specified_system_framework">'User-Specified' System Frameworks</a></li> | |
-<li><a href="#availability">Availability attribute</a></li> | |
-<li><a href="#checking_language_features">Checks for Standard Language Features</a> | |
- <ul> | |
- <li><a href="#cxx98">C++98</a> | |
- <ul> | |
- <li><a href="#cxx_exceptions">C++ exceptions</a></li> | |
- <li><a href="#cxx_rtti">C++ RTTI</a></li> | |
- </ul></li> | |
- <li><a href="#cxx11">C++11</a> | |
- <ul> | |
- <li><a href="#cxx_access_control_sfinae">C++11 SFINAE includes access control</a></li> | |
- <li><a href="#cxx_alias_templates">C++11 alias templates</a></li> | |
- <li><a href="#cxx_alignas">C++11 alignment specifiers</a></li> | |
- <li><a href="#cxx_attributes">C++11 attributes</a></li> | |
- <li><a href="#cxx_constexpr">C++11 generalized constant expressions</a></li> | |
- <li><a href="#cxx_decltype">C++11 <tt>decltype()</tt></a></li> | |
- <li><a href="#cxx_default_function_template_args">C++11 default template arguments in function templates</a></li> | |
- <li><a href="#cxx_defaulted_functions">C++11 defaulted functions</a></li> | |
- <li><a href="#cxx_delegating_constructor">C++11 delegating constructors</a></li> | |
- <li><a href="#cxx_deleted_functions">C++11 deleted functions</a></li> | |
- <li><a href="#cxx_explicit_conversions">C++11 explicit conversion functions</a></li> | |
- <li><a href="#cxx_generalized_initializers">C++11 generalized initializers</a></li> | |
- <li><a href="#cxx_implicit_moves">C++11 implicit move constructors/assignment operators</a></li> | |
- <li><a href="#cxx_inheriting_constructors">C++11 inheriting constructors</a></li> | |
- <li><a href="#cxx_inline_namespaces">C++11 inline namespaces</a></li> | |
- <li><a href="#cxx_lambdas">C++11 lambdas</a></li> | |
- <li><a href="#cxx_local_type_template_args">C++11 local and unnamed types as template arguments</a></li> | |
- <li><a href="#cxx_noexcept">C++11 noexcept specification</a></li> | |
- <li><a href="#cxx_nonstatic_member_init">C++11 in-class non-static data member initialization</a></li> | |
- <li><a href="#cxx_nullptr">C++11 nullptr</a></li> | |
- <li><a href="#cxx_override_control">C++11 override control</a></li> | |
- <li><a href="#cxx_range_for">C++11 range-based for loop</a></li> | |
- <li><a href="#cxx_raw_string_literals">C++11 raw string literals</a></li> | |
- <li><a href="#cxx_rvalue_references">C++11 rvalue references</a></li> | |
- <li><a href="#cxx_reference_qualified_functions">C++11 reference-qualified functions</a></li> | |
- <li><a href="#cxx_static_assert">C++11 <tt>static_assert()</tt></a></li> | |
- <li><a href="#cxx_auto_type">C++11 type inference</a></li> | |
- <li><a href="#cxx_strong_enums">C++11 strongly-typed enumerations</a></li> | |
- <li><a href="#cxx_trailing_return">C++11 trailing return type</a></li> | |
- <li><a href="#cxx_unicode_literals">C++11 Unicode string literals</a></li> | |
- <li><a href="#cxx_unrestricted_unions">C++11 unrestricted unions</a></li> | |
- <li><a href="#cxx_user_literals">C++11 user-defined literals</a></li> | |
- <li><a href="#cxx_variadic_templates">C++11 variadic templates</a></li> | |
- </ul></li> | |
- <li><a href="#c11">C11</a> | |
- <ul> | |
- <li><a href="#c_alignas">C11 alignment specifiers</a></li> | |
- <li><a href="#c_atomic">C11 atomic operations</a></li> | |
- <li><a href="#c_generic_selections">C11 generic selections</a></li> | |
- <li><a href="#c_static_assert">C11 <tt>_Static_assert()</tt></a></li> | |
- </ul></li> | |
-</ul></li> | |
-<li><a href="#checking_type_traits">Checks for Type Traits</a></li> | |
-<li><a href="#blocks">Blocks</a></li> | |
-<li><a href="#objc_features">Objective-C Features</a> | |
- <ul> | |
- <li><a href="#objc_instancetype">Related result types</a></li> | |
- <li><a href="#objc_arc">Automatic reference counting</a></li> | |
- <li><a href="#objc_fixed_enum">Enumerations with a fixed underlying type</a></li> | |
- <li><a href="#objc_lambdas">Interoperability with C++11 lambdas</a></li> | |
- <li><a href="#objc_object_literals_subscripting">Object Literals and Subscripting</a></li> | |
- </ul> | |
-</li> | |
-<li><a href="#overloading-in-c">Function Overloading in C</a></li> | |
-<li><a href="#complex-list-init">Initializer lists for complex numbers in C</a></li> | |
-<li><a href="#builtins">Builtin Functions</a> | |
- <ul> | |
- <li><a href="#__builtin_readcyclecounter">__builtin_readcyclecounter</a></li> | |
- <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li> | |
- <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li> | |
- <li><a href="#__sync_swap">__sync_swap</a></li> | |
- </ul> | |
-</li> | |
-<li><a href="#non-standard-attributes">Non-standard C++11 Attributes</a> | |
-<ul> | |
- <li><a href="#clang__fallthrough">The <tt>clang::fallthrough</tt> attribute</a></li> | |
-</ul> | |
-</li> | |
-<li><a href="#targetspecific">Target-Specific Extensions</a> | |
- <ul> | |
- <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li> | |
- </ul> | |
-</li> | |
-<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li> | |
-<li><a href="#dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</a> | |
- <ul> | |
- <li><a href="#address_sanitizer">AddressSanitizer</a></li> | |
- </ul> | |
-</li> | |
-<li><a href="#threadsafety">Thread Safety Annotation Checking</a> | |
- <ul> | |
- <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li> | |
- <li><a href="#ts_lockable"><tt>lockable</tt></a></li> | |
- <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li> | |
- <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li> | |
- <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li> | |
- <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li> | |
- <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li> | |
- <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li> | |
- <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li> | |
- <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li> | |
- <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li> | |
- <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li> | |
- <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li> | |
- <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li> | |
- <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li> | |
- <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li> | |
- <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li> | |
- <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li> | |
- </ul> | |
-</li> | |
-<li><a href="#type_safety">Type Safety Checking</a> | |
- <ul> | |
- <li><a href="#argument_with_type_tag"><tt>argument_with_type_tag(...)</tt></a></li> | |
- <li><a href="#pointer_with_type_tag"><tt>pointer_with_type_tag(...)</tt></a></li> | |
- <li><a href="#type_tag_for_datatype"><tt>type_tag_for_datatype(...)</tt></a></li> | |
- </ul> | |
-</li> | |
-</ul> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="intro">Introduction</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>This document describes the language extensions provided by Clang. In | |
-addition to the language extensions listed here, Clang aims to support a broad | |
-range of GCC extensions. Please see the <a | |
-href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for | |
-more information on these extensions.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="feature_check">Feature Checking Macros</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Language extensions can be very useful, but only if you know you can depend | |
-on them. In order to allow fine-grain features checks, we support three builtin | |
-function-like macros. This allows you to directly test for a feature in your | |
-code without having to resort to something like autoconf or fragile "compiler | |
-version checks".</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h3><a name="__has_builtin">__has_builtin</a></h3> | |
-<!-- ======================================================================= --> | |
- | |
-<p>This function-like macro takes a single identifier argument that is the name | |
-of a builtin function. It evaluates to 1 if the builtin is supported or 0 if | |
-not. It can be used like this:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-#ifndef __has_builtin // Optional of course. | |
- #define __has_builtin(x) 0 // Compatibility with non-clang compilers. | |
-#endif | |
- | |
-... | |
-#if __has_builtin(__builtin_trap) | |
- __builtin_trap(); | |
-#else | |
- abort(); | |
-#endif | |
-... | |
-</pre> | |
-</blockquote> | |
- | |
- | |
-<!-- ======================================================================= --> | |
-<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3> | |
-<!-- ======================================================================= --> | |
- | |
-<p>These function-like macros take a single identifier argument that is the | |
-name of a feature. <code>__has_feature</code> evaluates to 1 if the feature | |
-is both supported by Clang and standardized in the current language standard | |
-or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while | |
-<code>__has_extension</code> evaluates to 1 if the feature is supported by | |
-Clang in the current language (either as a language extension or a standard | |
-language feature) or 0 if not. They can be used like this:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-#ifndef __has_feature // Optional of course. | |
- #define __has_feature(x) 0 // Compatibility with non-clang compilers. | |
-#endif | |
-#ifndef __has_extension | |
- #define __has_extension __has_feature // Compatibility with pre-3.0 compilers. | |
-#endif | |
- | |
-... | |
-#if __has_feature(cxx_rvalue_references) | |
-// This code will only be compiled with the -std=c++11 and -std=gnu++11 | |
-// options, because rvalue references are only standardized in C++11. | |
-#endif | |
- | |
-#if __has_extension(cxx_rvalue_references) | |
-// This code will be compiled with the -std=c++11, -std=gnu++11, -std=c++98 | |
-// and -std=gnu++98 options, because rvalue references are supported as a | |
-// language extension in C++98. | |
-#endif | |
-</pre> | |
-</blockquote> | |
- | |
-<p id="has_feature_back_compat">For backwards compatibility reasons, | |
-<code>__has_feature</code> can also be used to test for support for | |
-non-standardized features, i.e. features not prefixed <code>c_</code>, | |
-<code>cxx_</code> or <code>objc_</code>.</p> | |
- | |
-<p id="has_feature_for_non_language_features"> | |
-Another use of <code>__has_feature</code> is to check for compiler features | |
-not related to the language standard, such as e.g. | |
-<a href="AddressSanitizer.html">AddressSanitizer</a>. | |
- | |
-<p>If the <code>-pedantic-errors</code> option is given, | |
-<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p> | |
- | |
-<p>The feature tag is described along with the language feature below.</p> | |
- | |
-<p>The feature name or extension name can also be specified with a preceding and | |
-following <code>__</code> (double underscore) to avoid interference from a macro | |
-with the same name. For instance, <code>__cxx_rvalue_references__</code> can be | |
-used instead of <code>cxx_rvalue_references</code>.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h3><a name="__has_attribute">__has_attribute</a></h3> | |
-<!-- ======================================================================= --> | |
- | |
-<p>This function-like macro takes a single identifier argument that is the name | |
-of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It | |
-can be used like this:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-#ifndef __has_attribute // Optional of course. | |
- #define __has_attribute(x) 0 // Compatibility with non-clang compilers. | |
-#endif | |
- | |
-... | |
-#if __has_attribute(always_inline) | |
-#define ALWAYS_INLINE __attribute__((always_inline)) | |
-#else | |
-#define ALWAYS_INLINE | |
-#endif | |
-... | |
-</pre> | |
-</blockquote> | |
- | |
-<p>The attribute name can also be specified with a preceding and | |
-following <code>__</code> (double underscore) to avoid interference from a macro | |
-with the same name. For instance, <code>__always_inline__</code> can be used | |
-instead of <code>always_inline</code>.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="has_include">Include File Checking Macros</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Not all developments systems have the same include files. | |
-The <a href="#__has_include">__has_include</a> and | |
-<a href="#__has_include_next">__has_include_next</a> macros allow you to | |
-check for the existence of an include file before doing | |
-a possibly failing #include directive.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h3><a name="__has_include">__has_include</a></h3> | |
-<!-- ======================================================================= --> | |
- | |
-<p>This function-like macro takes a single file name string argument that | |
-is the name of an include file. It evaluates to 1 if the file can | |
-be found using the include paths, or 0 otherwise:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-// Note the two possible file name string formats. | |
-#if __has_include("myinclude.h") && __has_include(<stdint.h>) | |
-# include "myinclude.h" | |
-#endif | |
- | |
-// To avoid problem with non-clang compilers not having this macro. | |
-#if defined(__has_include) && __has_include("myinclude.h") | |
-# include "myinclude.h" | |
-#endif | |
-</pre> | |
-</blockquote> | |
- | |
-<p>To test for this feature, use #if defined(__has_include).</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h3><a name="__has_include_next">__has_include_next</a></h3> | |
-<!-- ======================================================================= --> | |
- | |
-<p>This function-like macro takes a single file name string argument that | |
-is the name of an include file. It is like __has_include except that it | |
-looks for the second instance of the given file found in the include | |
-paths. It evaluates to 1 if the second instance of the file can | |
-be found using the include paths, or 0 otherwise:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-// Note the two possible file name string formats. | |
-#if __has_include_next("myinclude.h") && __has_include_next(<stdint.h>) | |
-# include_next "myinclude.h" | |
-#endif | |
- | |
-// To avoid problem with non-clang compilers not having this macro. | |
-#if defined(__has_include_next) && __has_include_next("myinclude.h") | |
-# include_next "myinclude.h" | |
-#endif | |
-</pre> | |
-</blockquote> | |
- | |
-<p>Note that __has_include_next, like the GNU extension | |
-#include_next directive, is intended for use in headers only, | |
-and will issue a warning if used in the top-level compilation | |
-file. A warning will also be issued if an absolute path | |
-is used in the file argument.</p> | |
- | |
- | |
-<!-- ======================================================================= --> | |
-<h3><a name="__has_warning">__has_warning</a></h3> | |
-<!-- ======================================================================= --> | |
- | |
-<p>This function-like macro takes a string literal that represents a command | |
- line option for a warning and returns true if that is a valid warning | |
- option.</p> | |
- | |
-<blockquote> | |
-<pre> | |
-#if __has_warning("-Wformat") | |
-... | |
-#endif | |
-</pre> | |
-</blockquote> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="builtinmacros">Builtin Macros</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<dl> | |
- <dt><code>__BASE_FILE__</code></dt> | |
- <dd>Defined to a string that contains the name of the main input | |
- file passed to Clang.</dd> | |
- | |
- <dt><code>__COUNTER__</code></dt> | |
- <dd>Defined to an integer value that starts at zero and is | |
- incremented each time the <code>__COUNTER__</code> macro is | |
- expanded.</dd> | |
- | |
- <dt><code>__INCLUDE_LEVEL__</code></dt> | |
- <dd>Defined to an integral value that is the include depth of the | |
- file currently being translated. For the main file, this value is | |
- zero.</dd> | |
- | |
- <dt><code>__TIMESTAMP__</code></dt> | |
- <dd>Defined to the date and time of the last modification of the | |
- current source file.</dd> | |
- | |
- <dt><code>__clang__</code></dt> | |
- <dd>Defined when compiling with Clang</dd> | |
- | |
- <dt><code>__clang_major__</code></dt> | |
- <dd>Defined to the major marketing version number of Clang (e.g., the | |
- 2 in 2.0.1). Note that marketing version numbers should not be used to | |
- check for language features, as different vendors use different numbering | |
- schemes. Instead, use the <a href="#feature_check">feature checking | |
- macros</a>.</dd> | |
- | |
- <dt><code>__clang_minor__</code></dt> | |
- <dd>Defined to the minor version number of Clang (e.g., the 0 in | |
- 2.0.1). Note that marketing version numbers should not be used to | |
- check for language features, as different vendors use different numbering | |
- schemes. Instead, use the <a href="#feature_check">feature checking | |
- macros</a>.</dd> | |
- | |
- <dt><code>__clang_patchlevel__</code></dt> | |
- <dd>Defined to the marketing patch level of Clang (e.g., the 1 in 2.0.1).</dd> | |
- | |
- <dt><code>__clang_version__</code></dt> | |
- <dd>Defined to a string that captures the Clang marketing version, including | |
- the Subversion tag or revision number, e.g., "1.5 (trunk 102332)".</dd> | |
-</dl> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="vectors">Vectors and Extended Vectors</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Supports the GCC, OpenCL, AltiVec and NEON vector extensions.</p> | |
- | |
-<p>OpenCL vector types are created using <tt>ext_vector_type</tt> attribute. It | |
-support for <tt>V.xyzw</tt> syntax and other tidbits as seen in OpenCL. An | |
-example is:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>; | |
-typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>; | |
- | |
-float4 foo(float2 a, float2 b) { | |
- float4 c; | |
- c.xz = a; | |
- c.yw = b; | |
- return c; | |
-} | |
-</pre> | |
-</blockquote> | |
- | |
-<p>Query for this feature with | |
-<tt>__has_extension(attribute_ext_vector_type)</tt>.</p> | |
- | |
-<p>Giving <tt>-faltivec</tt> option to clang enables support for AltiVec vector | |
-syntax and functions. For example:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-vector float foo(vector int a) { | |
- vector int b; | |
- b = vec_add(a, a) + a; | |
- return (vector float)b; | |
-} | |
-</pre> | |
-</blockquote> | |
- | |
-<p>NEON vector types are created using <tt>neon_vector_type</tt> and | |
-<tt>neon_polyvector_type</tt> attributes. For example:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-typedef <b>__attribute__((neon_vector_type(8)))</b> int8_t int8x8_t; | |
-typedef <b>__attribute__((neon_polyvector_type(16)))</b> poly8_t poly8x16_t; | |
- | |
-int8x8_t foo(int8x8_t a) { | |
- int8x8_t v; | |
- v = a; | |
- return v; | |
-} | |
-</pre> | |
-</blockquote> | |
- | |
-<!-- ======================================================================= --> | |
-<h3><a name="vector_literals">Vector Literals</a></h3> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Vector literals can be used to create vectors from a set of scalars, or | |
-vectors. Either parentheses or braces form can be used. In the parentheses form | |
-the number of literal values specified must be one, i.e. referring to a scalar | |
-value, or must match the size of the vector type being created. If a single | |
-scalar literal value is specified, the scalar literal value will be replicated | |
-to all the components of the vector type. In the brackets form any number of | |
-literals can be specified. For example:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-typedef int v4si __attribute__((__vector_size__(16))); | |
-typedef float float4 __attribute__((ext_vector_type(4))); | |
-typedef float float2 __attribute__((ext_vector_type(2))); | |
- | |
-v4si vsi = (v4si){1, 2, 3, 4}; | |
-float4 vf = (float4)(1.0f, 2.0f, 3.0f, 4.0f); | |
-vector int vi1 = (vector int)(1); // vi1 will be (1, 1, 1, 1). | |
-vector int vi2 = (vector int){1}; // vi2 will be (1, 0, 0, 0). | |
-vector int vi3 = (vector int)(1, 2); // error | |
-vector int vi4 = (vector int){1, 2}; // vi4 will be (1, 2, 0, 0). | |
-vector int vi5 = (vector int)(1, 2, 3, 4); | |
-float4 vf = (float4)((float2)(1.0f, 2.0f), (float2)(3.0f, 4.0f)); | |
-</pre> | |
-</blockquote> | |
- | |
-<!-- ======================================================================= --> | |
-<h3><a name="vector_operations">Vector Operations</a></h3> | |
-<!-- ======================================================================= --> | |
- | |
-<p>The table below shows the support for each operation by vector extension. | |
-A dash indicates that an operation is not accepted according to a corresponding | |
-specification.</p> | |
- | |
-<table width="500" border="1" cellspacing="0"> | |
- <tr> | |
- <th>Operator</th> | |
- <th>OpenCL</th> | |
- <th>AltiVec</th> | |
- <th>GCC</th> | |
- <th>NEON</th> | |
- </tr> | |
- <tr> | |
- <td>[]</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">-</td> | |
- </tr> | |
- <tr> | |
- <td>unary operators +, -</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">-</td> | |
- </tr> | |
- <tr> | |
- <td>++, --</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">-</td> | |
- <td align="center">-</td> | |
- </tr> | |
- <tr> | |
- <td>+, -, *, /, %</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">-</td> | |
- </tr> | |
- <tr> | |
- <td>bitwise operators &, |, ^, ~</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">-</td> | |
- </tr> | |
- <tr> | |
- <td>>>, <<</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">-</td> | |
- </tr> | |
- <tr> | |
- <td>!, &&,||</td> | |
- <td align="center">no</td> | |
- <td align="center">-</td> | |
- <td align="center">-</td> | |
- <td align="center">-</td> | |
- </tr> | |
- <tr> | |
- <td>==,!=, >, <, >=, <=</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">-</td> | |
- <td align="center">-</td> | |
- </tr> | |
- <tr> | |
- <td>=</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- </tr> | |
- <tr> | |
- <td>:?</td> | |
- <td align="center">yes</td> | |
- <td align="center">-</td> | |
- <td align="center">-</td> | |
- <td align="center">-</td> | |
- </tr> | |
- <tr> | |
- <td>sizeof</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- <td align="center">yes</td> | |
- </tr> | |
-</table> | |
- | |
-<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>An optional string message can be added to the <tt>deprecated</tt> | |
-and <tt>unavailable</tt> attributes. For example:</p> | |
- | |
-<blockquote> | |
-<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre> | |
-</blockquote> | |
- | |
-<p>If the deprecated or unavailable declaration is used, the message | |
-will be incorporated into the appropriate diagnostic:</p> | |
- | |
-<blockquote> | |
-<pre>harmless.c:4:3: warning: 'explode' is deprecated: extremely unsafe, use 'combust' instead!!! | |
- [-Wdeprecated-declarations] | |
- explode(); | |
- ^</pre> | |
-</blockquote> | |
- | |
-<p>Query for this feature | |
-with <tt>__has_extension(attribute_deprecated_with_message)</tt> | |
-and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang allows attributes to be written on individual enumerators. | |
-This allows enumerators to be deprecated, made unavailable, etc. The | |
-attribute must appear after the enumerator name and before any | |
-initializer, like so:</p> | |
- | |
-<blockquote> | |
-<pre>enum OperationMode { | |
- OM_Invalid, | |
- OM_Normal, | |
- OM_Terrified __attribute__((deprecated)), | |
- OM_AbortOnError __attribute__((deprecated)) = 4 | |
-};</pre> | |
-</blockquote> | |
- | |
-<p>Attributes on the <tt>enum</tt> declaration do not apply to | |
-individual enumerators.</p> | |
- | |
-<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="user_specified_system_framework">'User-Specified' System Frameworks</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang provides a mechanism by which frameworks can be built in such a way | |
-that they will always be treated as being 'system frameworks', even if they are | |
-not present in a system framework directory. This can be useful to system | |
-framework developers who want to be able to test building other applications | |
-with development builds of their framework, including the manner in which the | |
-compiler changes warning behavior for system headers.</p> | |
- | |
-<p>Framework developers can opt-in to this mechanism by creating a | |
-'.system_framework' file at the top-level of their framework. That is, the | |
-framework should have contents like:</p> | |
- | |
-<pre> | |
- .../TestFramework.framework | |
- .../TestFramework.framework/.system_framework | |
- .../TestFramework.framework/Headers | |
- .../TestFramework.framework/Headers/TestFramework.h | |
- ... | |
-</pre> | |
- | |
-<p>Clang will treat the presence of this file as an indicator that the framework | |
-should be treated as a system framework, regardless of how it was found in the | |
-framework search path. For consistency, we recommend that such files never be | |
-included in installed versions of the framework.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="availability">Availability attribute</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang introduces the <code>availability</code> attribute, which can | |
-be placed on declarations to describe the lifecycle of that | |
-declaration relative to operating system versions. Consider the function declaration for a hypothetical function <code>f</code>:</p> | |
- | |
-<pre> | |
-void f(void) __attribute__((availability(macosx,introduced=10.4,deprecated=10.6,obsoleted=10.7))); | |
-</pre> | |
- | |
-<p>The availability attribute states that <code>f</code> was introduced in Mac OS X 10.4, deprecated in Mac OS X 10.6, and obsoleted in Mac OS X 10.7. This information is used by Clang to determine when it is safe to use <code>f</code>: for example, if Clang is instructed to compile code for Mac OS X 10.5, a call to <code>f()</code> succeeds. If Clang is instructed to compile code for Mac OS X 10.6, the call succeeds but Clang emits a warning specifying that the function is deprecated. Finally, if Clang is instructed to compile code for Mac OS X 10.7, the call fails because <code>f()</code> is no longer available.</p> | |
- | |
-<p>The availablility attribute is a comma-separated list starting with the platform name and then including clauses specifying important milestones in the declaration's lifetime (in any order) along with additional information. Those clauses can be:</p> | |
- | |
-<dl> | |
- <dt>introduced=<i>version</i></dt> | |
- <dd>The first version in which this declaration was introduced.</dd> | |
- | |
- <dt>deprecated=<i>version</i></dt> | |
- <dd>The first version in which this declaration was deprecated, meaning that users should migrate away from this API.</dd> | |
- | |
- <dt>obsoleted=<i>version</i></dt> | |
- <dd>The first version in which this declaration was obsoleted, meaning that it was removed completely and can no longer be used.</dd> | |
- | |
- <dt>unavailable</dt> | |
- <dd>This declaration is never available on this platform.</dd> | |
- | |
- <dt>message=<i>string-literal</i></dt> | |
- <dd>Additional message text that Clang will provide when emitting a warning or error about use of a deprecated or obsoleted declaration. Useful to direct users to replacement APIs.</dd> | |
-</dl> | |
- | |
-<p>Multiple availability attributes can be placed on a declaration, which may correspond to different platforms. Only the availability attribute with the platform corresponding to the target platform will be used; any others will be ignored. If no availability attribute specifies availability for the current target platform, the availability attributes are ignored. Supported platforms are:</p> | |
- | |
-<dl> | |
- <dt>ios</dt> | |
- <dd>Apple's iOS operating system. The minimum deployment target is specified by the <code>-mios-version-min=<i>version</i></code> or <code>-miphoneos-version-min=<i>version</i></code> command-line arguments.</dd> | |
- | |
- <dt>macosx</dt> | |
- <dd>Apple's Mac OS X operating system. The minimum deployment target is specified by the <code>-mmacosx-version-min=<i>version</i></code> command-line argument.</dd> | |
-</dl> | |
- | |
-<p>A declaration can be used even when deploying back to a platform | |
-version prior to when the declaration was introduced. When this | |
-happens, the declaration is <a | |
- href="https://developer.apple.com/library/mac/#documentation/MacOSX/Conceptual/BPFrameworks/Concepts/WeakLinking.html">weakly | |
-linked</a>, as if the <code>weak_import</code> attribute were added to the declaration. A weakly-linked declaration may or may not be present a run-time, and a program can determine whether the declaration is present by checking whether the address of that declaration is non-NULL.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="checking_language_features">Checks for Standard Language Features</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>The <tt>__has_feature</tt> macro can be used to query if certain standard | |
-language features are enabled. The <tt>__has_extension</tt> macro can be used | |
-to query if language features are available as an extension when compiling for | |
-a standard which does not provide them. The features which can be tested are | |
-listed here.</p> | |
- | |
-<h3 id="cxx98">C++98</h3> | |
- | |
-<p>The features listed below are part of the C++98 standard. These features are | |
-enabled by default when compiling C++ code.</p> | |
- | |
-<h4 id="cxx_exceptions">C++ exceptions</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_exceptions)</tt> to determine if C++ exceptions have been enabled. For | |
-example, compiling code with <tt>-fno-exceptions</tt> disables C++ exceptions.</p> | |
- | |
-<h4 id="cxx_rtti">C++ RTTI</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_rtti)</tt> to determine if C++ RTTI has been enabled. For example, | |
-compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p> | |
- | |
-<h3 id="cxx11">C++11</h3> | |
- | |
-<p>The features listed below are part of the C++11 standard. As a result, all | |
-these features are enabled with the <tt>-std=c++11</tt> or <tt>-std=gnu++11</tt> | |
-option when compiling C++ code.</p> | |
- | |
-<h4 id="cxx_access_control_sfinae">C++11 SFINAE includes access control</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_access_control_sfinae)</tt> or <tt>__has_extension(cxx_access_control_sfinae)</tt> to determine whether access-control errors (e.g., calling a private constructor) are considered to be template argument deduction errors (aka SFINAE errors), per <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1170">C++ DR1170</a>.</p> | |
- | |
-<h4 id="cxx_alias_templates">C++11 alias templates</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or | |
-<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for | |
-C++11's alias declarations and alias templates is enabled.</p> | |
- | |
-<h4 id="cxx_alignas">C++11 alignment specifiers</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_alignas)</tt> or | |
-<tt>__has_extension(cxx_alignas)</tt> to determine if support for alignment | |
-specifiers using <tt>alignas</tt> is enabled.</p> | |
- | |
-<h4 id="cxx_attributes">C++11 attributes</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_attributes)</tt> or | |
-<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute | |
-parsing with C++11's square bracket notation is enabled.</p> | |
- | |
-<h4 id="cxx_constexpr">C++11 generalized constant expressions</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support | |
-for generalized constant expressions (e.g., <tt>constexpr</tt>) is | |
-enabled.</p> | |
- | |
-<h4 id="cxx_decltype">C++11 <tt>decltype()</tt></h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_decltype)</tt> or | |
-<tt>__has_extension(cxx_decltype)</tt> to determine if support for the | |
-<tt>decltype()</tt> specifier is enabled. C++11's <tt>decltype</tt> | |
-does not require type-completeness of a function call expression. | |
-Use <tt>__has_feature(cxx_decltype_incomplete_return_types)</tt> | |
-or <tt>__has_extension(cxx_decltype_incomplete_return_types)</tt> | |
-to determine if support for this feature is enabled.</p> | |
- | |
-<h4 id="cxx_default_function_template_args">C++11 default template arguments in function templates</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or | |
-<tt>__has_extension(cxx_default_function_template_args)</tt> to determine | |
-if support for default template arguments in function templates is enabled.</p> | |
- | |
-<h4 id="cxx_defaulted_functions">C++11 <tt>default</tt>ed functions</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_defaulted_functions)</tt> or | |
-<tt>__has_extension(cxx_defaulted_functions)</tt> to determine if support for | |
-defaulted function definitions (with <tt>= default</tt>) is enabled.</p> | |
- | |
-<h4 id="cxx_delegating_constructors">C++11 delegating constructors</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if | |
-support for delegating constructors is enabled.</p> | |
- | |
-<h4 id="cxx_deleted_functions">C++11 <tt>delete</tt>d functions</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or | |
-<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for | |
-deleted function definitions (with <tt>= delete</tt>) is enabled.</p> | |
- | |
-<h4 id="cxx_explicit_conversions">C++11 explicit conversion functions</h4> | |
-<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p> | |
- | |
-<h4 id="cxx_generalized_initializers">C++11 generalized initializers</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if | |
-support for generalized initializers (using braced lists and | |
-<tt>std::initializer_list</tt>) is enabled.</p> | |
- | |
-<h4 id="cxx_implicit_moves">C++11 implicit move constructors/assignment operators</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will | |
-implicitly generate move constructors and move assignment operators where needed.</p> | |
- | |
-<h4 id="cxx_inheriting_constructors">C++11 inheriting constructors</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_inheriting_constructors)</tt> to determine if support for inheriting constructors is enabled. Clang does not currently implement this feature.</p> | |
- | |
-<h4 id="cxx_inline_namespaces">C++11 inline namespaces</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or | |
-<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for | |
-inline namespaces is enabled.</p> | |
- | |
-<h4 id="cxx_lambdas">C++11 lambdas</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_lambdas)</tt> or | |
-<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas | |
-is enabled. </p> | |
- | |
-<h4 id="cxx_local_type_template_args">C++11 local and unnamed types as template arguments</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_local_type_template_args)</tt> or | |
-<tt>__has_extension(cxx_local_type_template_args)</tt> to determine if | |
-support for local and unnamed types as template arguments is enabled.</p> | |
- | |
-<h4 id="cxx_noexcept">C++11 noexcept</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_noexcept)</tt> or | |
-<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept | |
-exception specifications is enabled.</p> | |
- | |
-<h4 id="cxx_nonstatic_member_init">C++11 in-class non-static data member initialization</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_nonstatic_member_init)</tt> to determine whether in-class initialization of non-static data members is enabled.</p> | |
- | |
-<h4 id="cxx_nullptr">C++11 <tt>nullptr</tt></h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_nullptr)</tt> or | |
-<tt>__has_extension(cxx_nullptr)</tt> to determine if support for | |
-<tt>nullptr</tt> is enabled.</p> | |
- | |
-<h4 id="cxx_override_control">C++11 <tt>override control</tt></h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_override_control)</tt> or | |
-<tt>__has_extension(cxx_override_control)</tt> to determine if support for | |
-the override control keywords is enabled.</p> | |
- | |
-<h4 id="cxx_reference_qualified_functions">C++11 reference-qualified functions</h4> | |
-<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or | |
-<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine | |
-if support for reference-qualified functions (e.g., member functions with | |
-<code>&</code> or <code>&&</code> applied to <code>*this</code>) | |
-is enabled.</p> | |
- | |
-<h4 id="cxx_range_for">C++11 range-based <tt>for</tt> loop</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_range_for)</tt> or | |
-<tt>__has_extension(cxx_range_for)</tt> to determine if support for the | |
-range-based for loop is enabled. </p> | |
- | |
-<h4 id="cxx_raw_string_literals">C++11 raw string literals</h4> | |
-<p>Use <tt>__has_feature(cxx_raw_string_literals)</tt> to determine if support | |
-for raw string literals (e.g., <tt>R"x(foo\bar)x"</tt>) is enabled.</p> | |
- | |
-<h4 id="cxx_rvalue_references">C++11 rvalue references</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or | |
-<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for | |
-rvalue references is enabled. </p> | |
- | |
-<h4 id="cxx_static_assert">C++11 <tt>static_assert()</tt></h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_static_assert)</tt> or | |
-<tt>__has_extension(cxx_static_assert)</tt> to determine if support for | |
-compile-time assertions using <tt>static_assert</tt> is enabled.</p> | |
- | |
-<h4 id="cxx_auto_type">C++11 type inference</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_auto_type)</tt> or | |
-<tt>__has_extension(cxx_auto_type)</tt> to determine C++11 type inference is | |
-supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt> | |
-will instead be a storage class specifier, as in C or C++98.</p> | |
- | |
-<h4 id="cxx_strong_enums">C++11 strongly typed enumerations</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or | |
-<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for | |
-strongly typed, scoped enumerations is enabled.</p> | |
- | |
-<h4 id="cxx_trailing_return">C++11 trailing return type</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or | |
-<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the | |
-alternate function declaration syntax with trailing return type is enabled.</p> | |
- | |
-<h4 id="cxx_unicode_literals">C++11 Unicode string literals</h4> | |
-<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if | |
-support for Unicode string literals is enabled.</p> | |
- | |
-<h4 id="cxx_unrestricted_unions">C++11 unrestricted unions</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_unrestricted_unions)</tt> to determine if support for unrestricted unions is enabled.</p> | |
- | |
-<h4 id="cxx_user_literals">C++11 user-defined literals</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_user_literals)</tt> to determine if support for user-defined literals is enabled.</p> | |
- | |
-<h4 id="cxx_variadic_templates">C++11 variadic templates</h4> | |
- | |
-<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or | |
-<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support | |
-for variadic templates is enabled.</p> | |
- | |
-<h3 id="c11">C11</h3> | |
- | |
-<p>The features listed below are part of the C11 standard. As a result, all | |
-these features are enabled with the <tt>-std=c11</tt> or <tt>-std=gnu11</tt> | |
-option when compiling C code. Additionally, because these features are all | |
-backward-compatible, they are available as extensions in all language modes.</p> | |
- | |
-<h4 id="c_alignas">C11 alignment specifiers</h4> | |
- | |
-<p>Use <tt>__has_feature(c_alignas)</tt> or <tt>__has_extension(c_alignas)</tt> | |
-to determine if support for alignment specifiers using <tt>_Alignas</tt> | |
-is enabled.</p> | |
- | |
-<h4 id="c_atomic">C11 atomic operations</h4> | |
- | |
-<p>Use <tt>__has_feature(c_atomic)</tt> or <tt>__has_extension(c_atomic)</tt> | |
-to determine if support for atomic types using <tt>_Atomic</tt> is enabled. | |
-Clang also provides <a href="#__c11_atomic">a set of builtins</a> which can be | |
-used to implement the <tt><stdatomic.h></tt> operations on | |
-<tt>_Atomic</tt> types.</p> | |
- | |
-<h4 id="c_generic_selections">C11 generic selections</h4> | |
- | |
-<p>Use <tt>__has_feature(c_generic_selections)</tt> or | |
-<tt>__has_extension(c_generic_selections)</tt> to determine if support for | |
-generic selections is enabled.</p> | |
- | |
-<p>As an extension, the C11 generic selection expression is available in all | |
-languages supported by Clang. The syntax is the same as that given in the | |
-C11 standard.</p> | |
- | |
-<p>In C, type compatibility is decided according to the rules given in the | |
-appropriate standard, but in C++, which lacks the type compatibility rules | |
-used in C, types are considered compatible only if they are equivalent.</p> | |
- | |
-<h4 id="c_static_assert">C11 <tt>_Static_assert()</tt></h4> | |
- | |
-<p>Use <tt>__has_feature(c_static_assert)</tt> or | |
-<tt>__has_extension(c_static_assert)</tt> to determine if support for | |
-compile-time assertions using <tt>_Static_assert</tt> is enabled.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="checking_type_traits">Checks for Type Traits</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang supports the <a href="http://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html">GNU C++ type traits</a> and a subset of the <a href="http://msdn.microsoft.com/en-us/library/ms177194(v=VS.100).aspx">Microsoft Visual C++ Type traits</a>. For each supported type trait <code>__X</code>, <code>__has_extension(X)</code> indicates the presence of the type trait. For example: | |
-<blockquote> | |
-<pre> | |
-#if __has_extension(is_convertible_to) | |
-template<typename From, typename To> | |
-struct is_convertible_to { | |
- static const bool value = __is_convertible_to(From, To); | |
-}; | |
-#else | |
-// Emulate type trait | |
-#endif | |
-</pre> | |
-</blockquote> | |
- | |
-<p>The following type traits are supported by Clang:</p> | |
-<ul> | |
- <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li> | |
- <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li> | |
- <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li> | |
- <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li> | |
- <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li> | |
- <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li> | |
- <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li> | |
- <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li> | |
- <li><code>__is_abstract</code> (GNU, Microsoft)</li> | |
- <li><code>__is_base_of</code> (GNU, Microsoft)</li> | |
- <li><code>__is_class</code> (GNU, Microsoft)</li> | |
- <li><code>__is_convertible_to</code> (Microsoft)</li> | |
- <li><code>__is_empty</code> (GNU, Microsoft)</li> | |
- <li><code>__is_enum</code> (GNU, Microsoft)</li> | |
- <li><code>__is_interface_class</code> (Microsoft)</li> | |
- <li><code>__is_pod</code> (GNU, Microsoft)</li> | |
- <li><code>__is_polymorphic</code> (GNU, Microsoft)</li> | |
- <li><code>__is_union</code> (GNU, Microsoft)</li> | |
- <li><code>__is_literal(type)</code>: Determines whether the given type is a literal type</li> | |
- <li><code>__is_final</code>: Determines whether the given type is declared with a <code>final</code> class-virt-specifier.</li> | |
- <li><code>__underlying_type(type)</code>: Retrieves the underlying type for a given <code>enum</code> type. This trait is required to implement the C++11 standard library.</li> | |
- <li><code>__is_trivially_assignable(totype, fromtype)</code>: Determines whether a value of type <tt>totype</tt> can be assigned to from a value of type <tt>fromtype</tt> such that no non-trivial functions are called as part of that assignment. This trait is required to implement the C++11 standard library.</li> | |
- <li><code>__is_trivially_constructible(type, argtypes...)</code>: Determines whether a value of type <tt>type</tt> can be direct-initialized with arguments of types <tt>argtypes...</tt> such that no non-trivial functions are called as part of that initialization. This trait is required to implement the C++11 standard library.</li> | |
-</ul> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="blocks">Blocks</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>The syntax and high level language feature description is in <a | |
-href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI | |
-details for the clang implementation are in <a | |
-href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p> | |
- | |
- | |
-<p>Query for this feature with __has_extension(blocks).</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="objc_features">Objective-C Features</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<h3 id="objc_instancetype">Related result types</h3> | |
- | |
-<p>According to Cocoa conventions, Objective-C methods with certain names ("init", "alloc", etc.) always return objects that are an instance of the receiving class's type. Such methods are said to have a "related result type", meaning that a message send to one of these methods will have the same static type as an instance of the receiver class. For example, given the following classes:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-@interface NSObject | |
-+ (id)alloc; | |
-- (id)init; | |
-@end | |
- | |
-@interface NSArray : NSObject | |
-@end | |
-</pre> | |
-</blockquote> | |
- | |
-<p>and this common initialization pattern</p> | |
- | |
-<blockquote> | |
-<pre> | |
-NSArray *array = [[NSArray alloc] init]; | |
-</pre> | |
-</blockquote> | |
- | |
-<p>the type of the expression <code>[NSArray alloc]</code> is | |
-<code>NSArray*</code> because <code>alloc</code> implicitly has a | |
-related result type. Similarly, the type of the expression | |
-<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since | |
-<code>init</code> has a related result type and its receiver is known | |
-to have the type <code>NSArray *</code>. If neither <code>alloc</code> nor <code>init</code> had a related result type, the expressions would have had type <code>id</code>, as declared in the method signature.</p> | |
- | |
-<p>A method with a related result type can be declared by using the | |
-type <tt>instancetype</tt> as its result type. <tt>instancetype</tt> | |
-is a contextual keyword that is only permitted in the result type of | |
-an Objective-C method, e.g.</p> | |
- | |
-<pre> | |
-@interface A | |
-+ (<b>instancetype</b>)constructAnA; | |
-@end | |
-</pre> | |
- | |
-<p>The related result type can also be inferred for some methods. | |
-To determine whether a method has an inferred related result type, the first | |
-word in the camel-case selector (e.g., "init" in "initWithObjects") is | |
-considered, and the method will have a related result type if its return | |
-type is compatible with the type of its class and if</p> | |
- | |
-<ul> | |
- | |
- <li>the first word is "alloc" or "new", and the method is a class | |
- method, or</li> | |
- | |
- <li>the first word is "autorelease", "init", "retain", or "self", | |
- and the method is an instance method.</li> | |
- | |
-</ul> | |
- | |
-<p>If a method with a related result type is overridden by a subclass | |
-method, the subclass method must also return a type that is compatible | |
-with the subclass type. For example:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-@interface NSString : NSObject | |
-- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString | |
-@end | |
-</pre> | |
-</blockquote> | |
- | |
-<p>Related result types only affect the type of a message send or | |
-property access via the given method. In all other respects, a method | |
-with a related result type is treated the same way as method that | |
-returns <tt>id</tt>.</p> | |
- | |
-<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether | |
-the <tt>instancetype</tt> contextual keyword is available.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="objc_arc">Automatic reference counting </h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang provides support for <a href="AutomaticReferenceCounting.html">automated reference counting</a> in Objective-C, which eliminates the need for manual retain/release/autorelease message sends. There are two feature macros associated with automatic reference counting: <code>__has_feature(objc_arc)</code> indicates the availability of automated reference counting in general, while <code>__has_feature(objc_arc_weak)</code> indicates that automated reference counting also includes support for <code>__weak</code> pointers to Objective-C objects.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang provides support for C++11 enumerations with a fixed | |
-underlying type within Objective-C. For example, one can write an | |
-enumeration type as:</p> | |
- | |
-<pre> | |
-typedef enum : unsigned char { Red, Green, Blue } Color; | |
-</pre> | |
- | |
-<p>This specifies that the underlying type, which is used to store the | |
-enumeration value, is <tt>unsigned char</tt>.</p> | |
- | |
-<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether | |
-support for fixed underlying types is available in Objective-C.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="objc_lambdas">Interoperability with C++11 lambdas</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang provides interoperability between C++11 lambdas and | |
-blocks-based APIs, by permitting a lambda to be implicitly converted | |
-to a block pointer with the corresponding signature. For example, | |
-consider an API such as <code>NSArray</code>'s array-sorting | |
-method:</p> | |
- | |
-<pre> - (NSArray *)sortedArrayUsingComparator:(NSComparator)cmptr; </pre> | |
- | |
-<p><code>NSComparator</code> is simply a typedef for the block pointer | |
-<code>NSComparisonResult (^)(id, id)</code>, and parameters of this | |
-type are generally provided with block literals as arguments. However, | |
-one can also use a C++11 lambda so long as it provides the same | |
-signature (in this case, accepting two parameters of type | |
-<code>id</code> and returning an <code>NSComparisonResult</code>):</p> | |
- | |
-<pre> | |
- NSArray *array = @[@"string 1", @"string 21", @"string 12", @"String 11", | |
- @"String 02"]; | |
- const NSStringCompareOptions comparisonOptions | |
- = NSCaseInsensitiveSearch | NSNumericSearch | | |
- NSWidthInsensitiveSearch | NSForcedOrderingSearch; | |
- NSLocale *currentLocale = [NSLocale currentLocale]; | |
- NSArray *sorted | |
- = [array sortedArrayUsingComparator:<b>[=](id s1, id s2) -> NSComparisonResult { | |
- NSRange string1Range = NSMakeRange(0, [s1 length]); | |
- return [s1 compare:s2 options:comparisonOptions | |
- range:string1Range locale:currentLocale]; | |
- }</b>]; | |
- NSLog(@"sorted: %@", sorted); | |
-</pre> | |
- | |
-<p>This code relies on an implicit conversion from the type of the | |
-lambda expression (an unnamed, local class type called the <i>closure | |
-type</i>) to the corresponding block pointer type. The conversion | |
-itself is expressed by a conversion operator in that closure type | |
-that produces a block pointer with the same signature as the lambda | |
-itself, e.g.,</p> | |
- | |
-<pre> | |
- operator NSComparisonResult (^)(id, id)() const; | |
-</pre> | |
- | |
-<p>This conversion function returns a new block that simply forwards | |
-the two parameters to the lambda object (which it captures by copy), | |
-then returns the result. The returned block is first copied (with | |
-<tt>Block_copy</tt>) and then autoreleased. As an optimization, if a | |
-lambda expression is immediately converted to a block pointer (as in | |
-the first example, above), then the block is not copied and | |
-autoreleased: rather, it is given the same lifetime as a block literal | |
-written at that point in the program, which avoids the overhead of | |
-copying a block to the heap in the common case.</p> | |
- | |
-<p>The conversion from a lambda to a block pointer is only available | |
-in Objective-C++, and not in C++ with blocks, due to its use of | |
-Objective-C memory management (autorelease).</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="objc_object_literals_subscripting">Object Literals and Subscripting</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang provides support for <a href="ObjectiveCLiterals.html">Object Literals | |
-and Subscripting</a> in Objective-C, which simplifies common Objective-C | |
-programming patterns, makes programs more concise, and improves the safety of | |
-container creation. There are several feature macros associated with object | |
-literals and subscripting: <code>__has_feature(objc_array_literals)</code> | |
-tests the availability of array literals; | |
-<code>__has_feature(objc_dictionary_literals)</code> tests the availability of | |
-dictionary literals; <code>__has_feature(objc_subscripting)</code> tests the | |
-availability of object subscripting.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="objc_default_synthesize_properties">Objective-C Autosynthesis of Properties</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p> Clang provides support for autosynthesis of declared properties. Using this | |
-feature, clang provides default synthesis of those properties not declared @dynamic | |
-and not having user provided backing getter and setter methods. | |
-<code>__has_feature(objc_default_synthesize_properties)</code> checks for availability | |
-of this feature in version of clang being used.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="overloading-in-c">Function Overloading in C</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang provides support for C++ function overloading in C. Function | |
-overloading in C is introduced using the <tt>overloadable</tt> attribute. For | |
-example, one might provide several overloaded versions of a <tt>tgsin</tt> | |
-function that invokes the appropriate standard function computing the sine of a | |
-value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt> | |
-precision:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-#include <math.h> | |
-float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); } | |
-double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); } | |
-long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); } | |
-</pre> | |
-</blockquote> | |
- | |
-<p>Given these declarations, one can call <tt>tgsin</tt> with a | |
-<tt>float</tt> value to receive a <tt>float</tt> result, with a | |
-<tt>double</tt> to receive a <tt>double</tt> result, etc. Function | |
-overloading in C follows the rules of C++ function overloading to pick | |
-the best overload given the call arguments, with a few C-specific | |
-semantics:</p> | |
-<ul> | |
- <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long | |
- double</tt> is ranked as a floating-point promotion (per C99) rather | |
- than as a floating-point conversion (as in C++).</li> | |
- | |
- <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type | |
- <tt>U*</tt> is considered a pointer conversion (with conversion | |
- rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li> | |
- | |
- <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt> | |
- is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This | |
- conversion is given "conversion" rank.</li> | |
-</ul> | |
- | |
-<p>The declaration of <tt>overloadable</tt> functions is restricted to | |
-function declarations and definitions. Most importantly, if any | |
-function with a given name is given the <tt>overloadable</tt> | |
-attribute, then all function declarations and definitions with that | |
-name (and in that scope) must have the <tt>overloadable</tt> | |
-attribute. This rule even applies to redeclarations of functions whose original | |
-declaration had the <tt>overloadable</tt> attribute, e.g.,</p> | |
- | |
-<blockquote> | |
-<pre> | |
-int f(int) __attribute__((overloadable)); | |
-float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i> | |
- | |
-int g(int) __attribute__((overloadable)); | |
-int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i> | |
-</pre> | |
-</blockquote> | |
- | |
-<p>Functions marked <tt>overloadable</tt> must have | |
-prototypes. Therefore, the following code is ill-formed:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i> | |
-</pre> | |
-</blockquote> | |
- | |
-<p>However, <tt>overloadable</tt> functions are allowed to use a | |
-ellipsis even if there are no named parameters (as is permitted in C++). This feature is particularly useful when combined with the <tt>unavailable</tt> attribute:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i> | |
-</pre> | |
-</blockquote> | |
- | |
-<p>Functions declared with the <tt>overloadable</tt> attribute have | |
-their names mangled according to the same rules as C++ function | |
-names. For example, the three <tt>tgsin</tt> functions in our | |
-motivating example get the mangled names <tt>_Z5tgsinf</tt>, | |
-<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two | |
-caveats to this use of name mangling:</p> | |
- | |
-<ul> | |
- | |
- <li>Future versions of Clang may change the name mangling of | |
- functions overloaded in C, so you should not depend on an specific | |
- mangling. To be completely safe, we strongly urge the use of | |
- <tt>static inline</tt> with <tt>overloadable</tt> functions.</li> | |
- | |
- <li>The <tt>overloadable</tt> attribute has almost no meaning when | |
- used in C++, because names will already be mangled and functions are | |
- already overloadable. However, when an <tt>overloadable</tt> | |
- function occurs within an <tt>extern "C"</tt> linkage specification, | |
- it's name <i>will</i> be mangled in the same way as it would in | |
- C.</li> | |
-</ul> | |
- | |
-<p>Query for this feature with __has_extension(attribute_overloadable).</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>clang supports an extension which allows the following in C:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-#include <math.h> | |
-#include <complex.h> | |
-complex float x = { 1.0f, INFINITY }; // Init to (1, Inf) | |
-</pre> | |
-</blockquote> | |
- | |
-<p>This construct is useful because there is no way to separately | |
-initialize the real and imaginary parts of a complex variable in | |
-standard C, given that clang does not support <code>_Imaginary</code>. | |
-(clang also supports the <code>__real__</code> and <code>__imag__</code> | |
-extensions from gcc, which help in some cases, but are not usable in | |
-static initializers.) | |
- | |
-<p>Note that this extension does not allow eliding the braces; the | |
-meaning of the following two lines is different:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1) | |
-complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0) | |
-</pre> | |
-</blockquote> | |
- | |
-<p>This extension also works in C++ mode, as far as that goes, but does not | |
- apply to the C++ <code>std::complex</code>. (In C++11, list | |
- initialization allows the same syntax to be used with | |
- <code>std::complex</code> with the same meaning.) | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="builtins">Builtin Functions</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang supports a number of builtin library functions with the same syntax as | |
-GCC, including things like <tt>__builtin_nan</tt>, | |
-<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>, | |
-<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In | |
-addition to the GCC builtins, Clang supports a number of builtins that GCC does | |
-not, which are listed here.</p> | |
- | |
-<p>Please note that Clang does not and will not support all of the GCC builtins | |
-for vector operations. Instead of using builtins, you should use the functions | |
-defined in target-specific header files like <tt><xmmintrin.h></tt>, which | |
-define portable wrappers for these. Many of the Clang versions of these | |
-functions are implemented directly in terms of <a href="#vectors">extended | |
-vector support</a> instead of builtins, in order to reduce the number of | |
-builtins that we need to implement.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h3><a name="__builtin_readcyclecounter">__builtin_readcyclecounter</a></h3> | |
-<!-- ======================================================================= --> | |
- | |
-<p><tt>__builtin_readcyclecounter</tt> is used to access the cycle counter | |
-register (or a similar low-latency, high-accuracy clock) on those targets that | |
-support it. | |
-</p> | |
- | |
-<p><b>Syntax:</b></p> | |
- | |
-<pre> | |
-__builtin_readcyclecounter() | |
-</pre> | |
- | |
-<p><b>Example of Use:</b></p> | |
- | |
-<pre> | |
-unsigned long long t0 = __builtin_readcyclecounter(); | |
-do_something(); | |
-unsigned long long t1 = __builtin_readcyclecounter(); | |
-unsigned long long cycles_to_do_something = t1 - t0; // assuming no overflow | |
-</pre> | |
- | |
-<p><b>Description:</b></p> | |
- | |
-<p>The __builtin_readcyclecounter() builtin returns the cycle counter value, | |
-which may be either global or process/thread-specific depending on the target. | |
-As the backing counters often overflow quickly (on the order of | |
-seconds) this should only be used for timing small intervals. When not | |
-supported by the target, the return value is always zero. This builtin | |
-takes no arguments and produces an unsigned long long result. | |
-</p> | |
- | |
-<p>Query for this feature with __has_builtin(__builtin_readcyclecounter).</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3> | |
-<!-- ======================================================================= --> | |
- | |
-<p><tt>__builtin_shufflevector</tt> is used to express generic vector | |
-permutation/shuffle/swizzle operations. This builtin is also very important for | |
-the implementation of various target-specific header files like | |
-<tt><xmmintrin.h></tt>. | |
-</p> | |
- | |
-<p><b>Syntax:</b></p> | |
- | |
-<pre> | |
-__builtin_shufflevector(vec1, vec2, index1, index2, ...) | |
-</pre> | |
- | |
-<p><b>Examples:</b></p> | |
- | |
-<pre> | |
- // Identity operation - return 4-element vector V1. | |
- __builtin_shufflevector(V1, V1, 0, 1, 2, 3) | |
- | |
- // "Splat" element 0 of V1 into a 4-element result. | |
- __builtin_shufflevector(V1, V1, 0, 0, 0, 0) | |
- | |
- // Reverse 4-element vector V1. | |
- __builtin_shufflevector(V1, V1, 3, 2, 1, 0) | |
- | |
- // Concatenate every other element of 4-element vectors V1 and V2. | |
- __builtin_shufflevector(V1, V2, 0, 2, 4, 6) | |
- | |
- // Concatenate every other element of 8-element vectors V1 and V2. | |
- __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14) | |
-</pre> | |
- | |
-<p><b>Description:</b></p> | |
- | |
-<p>The first two arguments to __builtin_shufflevector are vectors that have the | |
-same element type. The remaining arguments are a list of integers that specify | |
-the elements indices of the first two vectors that should be extracted and | |
-returned in a new vector. These element indices are numbered sequentially | |
-starting with the first vector, continuing into the second vector. Thus, if | |
-vec1 is a 4-element vector, index 5 would refer to the second element of vec2. | |
-</p> | |
- | |
-<p>The result of __builtin_shufflevector is a vector | |
-with the same element type as vec1/vec2 but that has an element count equal to | |
-the number of indices specified. | |
-</p> | |
- | |
-<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3> | |
-<!-- ======================================================================= --> | |
- | |
-<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in | |
-the program cannot be reached, even if the compiler might otherwise think it | |
-can. This is useful to improve optimization and eliminates certain warnings. | |
-For example, without the <tt>__builtin_unreachable</tt> in the example below, | |
-the compiler assumes that the inline asm can fall through and prints a "function | |
-declared 'noreturn' should not return" warning. | |
-</p> | |
- | |
-<p><b>Syntax:</b></p> | |
- | |
-<pre> | |
-__builtin_unreachable() | |
-</pre> | |
- | |
-<p><b>Example of Use:</b></p> | |
- | |
-<pre> | |
-void myabort(void) __attribute__((noreturn)); | |
-void myabort(void) { | |
- asm("int3"); | |
- __builtin_unreachable(); | |
-} | |
-</pre> | |
- | |
-<p><b>Description:</b></p> | |
- | |
-<p>The __builtin_unreachable() builtin has completely undefined behavior. Since | |
-it has undefined behavior, it is a statement that it is never reached and the | |
-optimizer can take advantage of this to produce better code. This builtin takes | |
-no arguments and produces a void result. | |
-</p> | |
- | |
-<p>Query for this feature with __has_builtin(__builtin_unreachable).</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h3><a name="__sync_swap">__sync_swap</a></h3> | |
-<!-- ======================================================================= --> | |
- | |
-<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in | |
-memory. | |
-</p> | |
- | |
-<p><b>Syntax:</b></p> | |
- | |
-<pre> | |
-<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...) | |
-</pre> | |
- | |
-<p><b>Example of Use:</b></p> | |
- | |
-<pre> | |
-int old_value = __sync_swap(&value, new_value); | |
-</pre> | |
- | |
-<p><b>Description:</b></p> | |
- | |
-<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic | |
-intrinsics to allow code to atomically swap the current value with the new | |
-value. More importantly, it helps developers write more efficient and correct | |
-code by avoiding expensive loops around __sync_bool_compare_and_swap() or | |
-relying on the platform specific implementation details of | |
-__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier. | |
-</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h3><a name="__c11_atomic">__c11_atomic builtins</a></h3> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang provides a set of builtins which are intended to be used to implement | |
-C11's <tt><stdatomic.h></tt> header. These builtins provide the semantics | |
-of the <tt>_explicit</tt> form of the corresponding C11 operation, and are named | |
-with a <tt>__c11_</tt> prefix. The supported operations are:</p> | |
- | |
-<ul> | |
- <li><tt>__c11_atomic_init</tt></li> | |
- <li><tt>__c11_atomic_thread_fence</tt></li> | |
- <li><tt>__c11_atomic_signal_fence</tt></li> | |
- <li><tt>__c11_atomic_is_lock_free</tt></li> | |
- <li><tt>__c11_atomic_store</tt></li> | |
- <li><tt>__c11_atomic_load</tt></li> | |
- <li><tt>__c11_atomic_exchange</tt></li> | |
- <li><tt>__c11_atomic_compare_exchange_strong</tt></li> | |
- <li><tt>__c11_atomic_compare_exchange_weak</tt></li> | |
- <li><tt>__c11_atomic_fetch_add</tt></li> | |
- <li><tt>__c11_atomic_fetch_sub</tt></li> | |
- <li><tt>__c11_atomic_fetch_and</tt></li> | |
- <li><tt>__c11_atomic_fetch_or</tt></li> | |
- <li><tt>__c11_atomic_fetch_xor</tt></li> | |
-</ul> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="non-standard-attributes">Non-standard C++11 Attributes</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang supports one non-standard C++11 attribute. It resides in the | |
-<tt>clang</tt> attribute namespace.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h3 id="clang__fallthrough">The <tt>clang::fallthrough</tt> attribute</h3> | |
-<!-- ======================================================================= --> | |
- | |
-<p>The <tt>clang::fallthrough</tt> attribute is used along with the | |
-<tt>-Wimplicit-fallthrough</tt> argument to annotate intentional fall-through | |
-between switch labels. It can only be applied to a null statement placed at a | |
-point of execution between any statement and the next switch label. It is common | |
-to mark these places with a specific comment, but this attribute is meant to | |
-replace comments with a more strict annotation, which can be checked by the | |
-compiler. This attribute doesn't change semantics of the code and can be used | |
-wherever an intended fall-through occurs. It is designed to mimic | |
-control-flow statements like <tt>break;</tt>, so it can be placed in most places | |
-where <tt>break;</tt> can, but only if there are no statements on the execution | |
-path between it and the next switch label.</p> | |
-<p>Here is an example:</p> | |
-<pre> | |
-// compile with -Wimplicit-fallthrough | |
-switch (n) { | |
-case 22: | |
-case 33: // no warning: no statements between case labels | |
- f(); | |
-case 44: // warning: unannotated fall-through | |
- g(); | |
- <b>[[clang::fallthrough]];</b> | |
-case 55: // no warning | |
- if (x) { | |
- h(); | |
- break; | |
- } | |
- else { | |
- i(); | |
- <b>[[clang::fallthrough]];</b> | |
- } | |
-case 66: // no warning | |
- p(); | |
- <b>[[clang::fallthrough]];</b> // warning: fallthrough annotation does not directly precede case label | |
- q(); | |
-case 77: // warning: unannotated fall-through | |
- r(); | |
-} | |
-</pre> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="targetspecific">Target-Specific Extensions</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang supports some language features conditionally on some targets.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h3 id="x86-specific">X86/X86-64 Language Extensions</h3> | |
-<!-- ======================================================================= --> | |
- | |
-<p>The X86 backend has these language extensions:</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h4 id="x86-gs-segment">Memory references off the GS segment</h4> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Annotating a pointer with address space #256 causes it to be code generated | |
-relative to the X86 GS segment register, and address space #257 causes it to be | |
-relative to the X86 FS segment. Note that this is a very very low-level | |
-feature that should only be used if you know what you're doing (for example in | |
-an OS kernel).</p> | |
- | |
-<p>Here is an example:</p> | |
- | |
-<pre> | |
-#define GS_RELATIVE __attribute__((address_space(256))) | |
-int foo(int GS_RELATIVE *P) { | |
- return *P; | |
-} | |
-</pre> | |
- | |
-<p>Which compiles to (on X86-32):</p> | |
- | |
-<pre> | |
-_foo: | |
- movl 4(%esp), %eax | |
- movl %gs:(%eax), %eax | |
- ret | |
-</pre> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang supports additional attributes that are useful for documenting program | |
-invariants and rules for static analysis tools. The extensions documented here | |
-are used by the <a | |
-href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer | |
-engine</a> that is part of Clang's Analysis library.</p> | |
- | |
-<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3> | |
- | |
-<p>Clang's static analysis engine understands the standard <tt>noreturn</tt> | |
-attribute. This attribute, which is typically affixed to a function prototype, | |
-indicates that a call to a given function never returns. Function prototypes for | |
-common functions like <tt>exit</tt> are typically annotated with this attribute, | |
-as well as a variety of common assertion handlers. Users can educate the static | |
-analyzer about their own custom assertion handles (thus cutting down on false | |
-positives due to false paths) by marking their own "panic" functions | |
-with this attribute.</p> | |
- | |
-<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes | |
-there are special functions that for all intents and purposes should be | |
-considered panic functions (i.e., they are only called when an internal program | |
-error occurs) but may actually return so that the program can fail gracefully. | |
-The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions | |
-as being interpreted as "no return" functions by the analyzer (thus | |
-pruning bogus paths) but will not affect compilation (as in the case of | |
-<tt>noreturn</tt>).</p> | |
- | |
-<p><b>Usage</b>: The <tt>analyzer_noreturn</tt> attribute can be placed in the | |
-same places where the <tt>noreturn</tt> attribute can be placed. It is commonly | |
-placed at the end of function prototypes:</p> | |
- | |
-<pre> | |
- void foo() <b>__attribute__((analyzer_noreturn))</b>; | |
-</pre> | |
- | |
-<p>Query for this feature with | |
-<tt>__has_attribute(analyzer_noreturn)</tt>.</p> | |
- | |
-<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3> | |
- | |
-<p>Many methods in Objective-C have conventional meanings determined | |
-by their selectors. For the purposes of static analysis, it is | |
-sometimes useful to be able to mark a method as having a particular | |
-conventional meaning despite not having the right selector, or as not | |
-having the conventional meaning that its selector would suggest. | |
-For these use cases, we provide an attribute to specifically describe | |
-the <q>method family</q> that a method belongs to.</p> | |
- | |
-<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>, | |
-where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>, | |
-<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute | |
-can only be placed at the end of a method declaration:</p> | |
- | |
-<pre> | |
- - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>; | |
-</pre> | |
- | |
-<p>Users who do not wish to change the conventional meaning of a | |
-method, and who merely want to document its non-standard retain and | |
-release semantics, should use the | |
-<a href="#attr_retain_release">retaining behavior attributes</a> | |
-described below.</p> | |
- | |
-<p>Query for this feature with | |
-<tt>__has_attribute(objc_method_family)</tt>.</p> | |
- | |
-<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3> | |
- | |
-<p>In Objective-C, functions and methods are generally assumed to take | |
-and return objects with +0 retain counts, with some exceptions for | |
-special methods like <tt>+alloc</tt> and <tt>init</tt>. However, | |
-there are exceptions, and so Clang provides attributes to allow these | |
-exceptions to be documented, which helps the analyzer find leaks (and | |
-ignore non-leaks). Some exceptions may be better described using | |
-the <a href="#attr_method_family"><tt>objc_method_family</tt></a> | |
-attribute instead.</p> | |
- | |
-<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>, | |
-<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>, | |
-and <tt>cf_returns_not_retained</tt> attributes can be placed on | |
-methods and functions that return Objective-C or CoreFoundation | |
-objects. They are commonly placed at the end of a function prototype | |
-or method declaration:</p> | |
- | |
-<pre> | |
- id foo() <b>__attribute__((ns_returns_retained))</b>; | |
- | |
- - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>; | |
-</pre> | |
- | |
-<p>The <tt>*_returns_retained</tt> attributes specify that the | |
-returned object has a +1 retain count. | |
-The <tt>*_returns_not_retained</tt> attributes specify that the return | |
-object has a +0 retain count, even if the normal convention for its | |
-selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the | |
-returned object is +0, but is guaranteed to live at least as long as the | |
-next flush of an autorelease pool.</p> | |
- | |
-<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt> | |
-attributes can be placed on an parameter declaration; they specify | |
-that the argument is expected to have a +1 retain count, which will be | |
-balanced in some way by the function or method. | |
-The <tt>ns_consumes_self</tt> attribute can only be placed on an | |
-Objective-C method; it specifies that the method expects | |
-its <tt>self</tt> parameter to have a +1 retain count, which it will | |
-balance in some way.</p> | |
- | |
-<pre> | |
- void <b>foo(__attribute__((ns_consumed))</b> NSString *string); | |
- | |
- - (void) bar <b>__attribute__((ns_consumes_self))</b>; | |
- - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x; | |
-</pre> | |
- | |
-<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>, | |
-<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</h2> | |
-<!-- ======================================================================= --> | |
-<h3 id="address_sanitizer">AddressSanitizer</h3> | |
-<p> Use <code>__has_feature(address_sanitizer)</code> | |
-to check if the code is being built with <a | |
- href="AddressSanitizer.html">AddressSanitizer</a>. | |
-</p> | |
-<p>Use <tt>__attribute__((no_address_safety_analysis))</tt> on a function | |
-declaration to specify that address safety instrumentation (e.g. | |
-AddressSanitizer) should not be applied to that function. | |
-</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="threadsafety">Thread-Safety Annotation Checking</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang supports additional attributes for checking basic locking policies in | |
-multithreaded programs. | |
-Clang currently parses the following list of attributes, although | |
-<b>the implementation for these annotations is currently in development.</b> | |
-For more details, see the | |
-<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>. | |
-</p> | |
- | |
-<h4 id="ts_noanal">no_thread_safety_analysis</h4> | |
- | |
-<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function | |
-declaration to specify that the thread safety analysis should not be run on that | |
-function. This attribute provides an escape hatch (e.g. for situations when it | |
-is difficult to annotate the locking policy). </p> | |
- | |
-<h4 id="ts_lockable">lockable</h4> | |
- | |
-<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify | |
-that it has a lockable type (e.g. a Mutex class). This annotation is primarily | |
-used to check consistency.</p> | |
- | |
-<h4 id="ts_scopedlockable">scoped_lockable</h4> | |
- | |
-<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to | |
-specify that it has a "scoped" lockable type. Objects of this type will acquire | |
-the lock upon construction and release it upon going out of scope. | |
- This annotation is primarily used to check | |
-consistency.</p> | |
- | |
-<h4 id="ts_guardedvar">guarded_var</h4> | |
- | |
-<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to | |
-specify that the variable must be accessed while holding some lock.</p> | |
- | |
-<h4 id="ts_ptguardedvar">pt_guarded_var</h4> | |
- | |
-<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to | |
-specify that the pointer must be dereferenced while holding some lock.</p> | |
- | |
-<h4 id="ts_guardedby">guarded_by(l)</h4> | |
- | |
-<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to | |
-specify that the variable must be accessed while holding lock <tt>l</tt>.</p> | |
- | |
-<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4> | |
- | |
-<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to | |
-specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p> | |
- | |
-<h4 id="ts_acquiredbefore">acquired_before(...)</h4> | |
- | |
-<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration | |
-of a lockable variable to specify that the lock must be acquired before all | |
-attribute arguments. Arguments must be lockable type, and there must be at | |
-least one argument.</p> | |
- | |
-<h4 id="ts_acquiredafter">acquired_after(...)</h4> | |
- | |
-<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration | |
-of a lockable variable to specify that the lock must be acquired after all | |
-attribute arguments. Arguments must be lockable type, and there must be at | |
-least one argument.</p> | |
- | |
-<h4 id="ts_elf">exclusive_lock_function(...)</h4> | |
- | |
-<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function | |
-declaration to specify that the function acquires all listed locks | |
-exclusively. This attribute takes zero or more arguments: either of lockable | |
-type or integers indexing into function parameters of lockable type. If no | |
-arguments are given, the acquired lock is implicitly <tt>this</tt> of the | |
-enclosing object.</p> | |
- | |
-<h4 id="ts_slf">shared_lock_function(...)</h4> | |
- | |
-<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function | |
-declaration to specify that the function acquires all listed locks, although | |
- the locks may be shared (e.g. read locks). This attribute takes zero or more | |
-arguments: either of lockable type or integers indexing into function | |
-parameters of lockable type. If no arguments are given, the acquired lock is | |
-implicitly <tt>this</tt> of the enclosing object.</p> | |
- | |
-<h4 id="ts_etf">exclusive_trylock_function(...)</h4> | |
- | |
-<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function | |
-declaration to specify that the function will try (without blocking) to acquire | |
-all listed locks exclusively. This attribute takes one or more arguments. The | |
-first argument is an integer or boolean value specifying the return value of a | |
-successful lock acquisition. The remaining arugments are either of lockable type | |
-or integers indexing into function parameters of lockable type. If only one | |
-argument is given, the acquired lock is implicitly <tt>this</tt> of the | |
-enclosing object.</p> | |
- | |
-<h4 id="ts_stf">shared_trylock_function(...)</h4> | |
- | |
-<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function | |
-declaration to specify that the function will try (without blocking) to acquire | |
-all listed locks, although the locks may be shared (e.g. read locks). This | |
-attribute takes one or more arguments. The first argument is an integer or | |
-boolean value specifying the return value of a successful lock acquisition. The | |
-remaining arugments are either of lockable type or integers indexing into | |
-function parameters of lockable type. If only one argument is given, the | |
-acquired lock is implicitly <tt>this</tt> of the enclosing object.</p> | |
- | |
-<h4 id="ts_uf">unlock_function(...)</h4> | |
- | |
-<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function | |
-declaration to specify that the function release all listed locks. This | |
-attribute takes zero or more arguments: either of lockable type or integers | |
-indexing into function parameters of lockable type. If no arguments are given, | |
-the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p> | |
- | |
-<h4 id="ts_lr">lock_returned(l)</h4> | |
- | |
-<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function | |
-declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt> | |
-must be of lockable type). This annotation is used to aid in resolving lock | |
-expressions.</p> | |
- | |
-<h4 id="ts_le">locks_excluded(...)</h4> | |
- | |
-<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration | |
-to specify that the function must not be called with the listed locks. Arguments | |
-must be lockable type, and there must be at least one argument.</p> | |
- | |
-<h4 id="ts_elr">exclusive_locks_required(...)</h4> | |
- | |
-<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function | |
-declaration to specify that the function must be called while holding the listed | |
-exclusive locks. Arguments must be lockable type, and there must be at | |
-least one argument.</p> | |
- | |
-<h4 id="ts_slr">shared_locks_required(...)</h4> | |
- | |
-<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function | |
-declaration to specify that the function must be called while holding the listed | |
-shared locks. Arguments must be lockable type, and there must be at | |
-least one argument.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="type_safety">Type Safety Checking</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang supports additional attributes to enable checking type safety | |
-properties that can't be enforced by C type system. Usecases include:</p> | |
-<ul> | |
-<li>MPI library implementations, where these attributes enable checking that | |
- buffer type matches the passed <tt>MPI_Datatype</tt>;</li> | |
-<li>for HDF5 library there is a similar usecase as MPI;</li> | |
-<li>checking types of variadic functions' arguments for functions like | |
- <tt>fcntl()</tt> and <tt>ioctl()</tt>.</li> | |
-</ul> | |
- | |
-<p>You can detect support for these attributes with __has_attribute(). For | |
-example:</p> | |
- | |
-<blockquote> | |
-<pre> | |
-#if defined(__has_attribute) | |
-# if __has_attribute(argument_with_type_tag) && \ | |
- __has_attribute(pointer_with_type_tag) && \ | |
- __has_attribute(type_tag_for_datatype) | |
-# define ATTR_MPI_PWT(buffer_idx, type_idx) __attribute__((pointer_with_type_tag(mpi,buffer_idx,type_idx))) | |
-/* ... other macros ... */ | |
-# endif | |
-#endif | |
- | |
-#if !defined(ATTR_MPI_PWT) | |
-#define ATTR_MPI_PWT(buffer_idx, type_idx) | |
-#endif | |
- | |
-int MPI_Send(void *buf, int count, MPI_Datatype datatype /*, other args omitted */) | |
- ATTR_MPI_PWT(1,3); | |
-</pre> | |
-</blockquote> | |
- | |
-<h3 id="argument_with_type_tag"><tt>argument_with_type_tag(...)</tt></h3> | |
- | |
-<p>Use <tt>__attribute__((argument_with_type_tag(arg_kind, arg_idx, | |
-type_tag_idx)))</tt> on a function declaration to specify that the function | |
-accepts a type tag that determines the type of some other argument. | |
-<tt>arg_kind</tt> is an identifier that should be used when annotating all | |
-applicable type tags.</p> | |
- | |
-<p>This attribute is primarily useful for checking arguments of variadic | |
-functions (<tt>pointer_with_type_tag</tt> can be used in most of non-variadic | |
-cases).</p> | |
- | |
-<p>For example:</p> | |
-<blockquote> | |
-<pre> | |
-int fcntl(int fd, int cmd, ...) | |
- __attribute__(( argument_with_type_tag(fcntl,3,2) )); | |
-</pre> | |
-</blockquote> | |
- | |
-<h3 id="pointer_with_type_tag"><tt>pointer_with_type_tag(...)</tt></h3> | |
- | |
-<p>Use <tt>__attribute__((pointer_with_type_tag(ptr_kind, ptr_idx, | |
-type_tag_idx)))</tt> on a function declaration to specify that the | |
-function accepts a type tag that determines the pointee type of some other | |
-pointer argument.</p> | |
- | |
-<p>For example:</p> | |
-<blockquote> | |
-<pre> | |
-int MPI_Send(void *buf, int count, MPI_Datatype datatype /*, other args omitted */) | |
- __attribute__(( pointer_with_type_tag(mpi,1,3) )); | |
-</pre> | |
-</blockquote> | |
- | |
-<h3 id="type_tag_for_datatype"><tt>type_tag_for_datatype(...)</tt></h3> | |
- | |
-<p>Clang supports annotating type tags of two forms.</p> | |
- | |
-<ul> | |
-<li><b>Type tag that is an expression containing a reference to some declared | |
-identifier.</b> Use <tt>__attribute__((type_tag_for_datatype(kind, type)))</tt> | |
-on a declaration with that identifier: | |
- | |
-<blockquote> | |
-<pre> | |
-extern struct mpi_datatype mpi_datatype_int | |
- __attribute__(( type_tag_for_datatype(mpi,int) )); | |
-#define MPI_INT ((MPI_Datatype) &mpi_datatype_int) | |
-</pre> | |
-</blockquote></li> | |
- | |
-<li><b>Type tag that is an integral literal.</b> Introduce a <tt>static | |
-const</tt> variable with a corresponding initializer value and attach | |
-<tt>__attribute__((type_tag_for_datatype(kind, type)))</tt> on that | |
-declaration, for example: | |
- | |
-<blockquote> | |
-<pre> | |
-#define MPI_INT ((MPI_Datatype) 42) | |
-static const MPI_Datatype mpi_datatype_int | |
- __attribute__(( type_tag_for_datatype(mpi,int) )) = 42 | |
-</pre> | |
-</blockquote></li> | |
-</ul> | |
- | |
-<p>The attribute also accepts an optional third argument that determines how | |
-the expression is compared to the type tag. There are two supported flags:</p> | |
- | |
-<ul><li><tt>layout_compatible</tt> will cause types to be compared according to | |
-layout-compatibility rules (C++11 [class.mem] p 17, 18). This is | |
-implemented to support annotating types like <tt>MPI_DOUBLE_INT</tt>. | |
- | |
-<p>For example:</p> | |
-<blockquote> | |
-<pre> | |
-/* In mpi.h */ | |
-struct internal_mpi_double_int { double d; int i; }; | |
-extern struct mpi_datatype mpi_datatype_double_int | |
- __attribute__(( type_tag_for_datatype(mpi, struct internal_mpi_double_int, | |
- layout_compatible) )); | |
- | |
-#define MPI_DOUBLE_INT ((MPI_Datatype) &mpi_datatype_double_int) | |
- | |
-/* In user code */ | |
-struct my_pair { double a; int b; }; | |
-struct my_pair *buffer; | |
-MPI_Send(buffer, 1, MPI_DOUBLE_INT /*, ... */); // no warning | |
- | |
-struct my_int_pair { int a; int b; } | |
-struct my_int_pair *buffer2; | |
-MPI_Send(buffer2, 1, MPI_DOUBLE_INT /*, ... */); // warning: actual buffer element | |
- // type 'struct my_int_pair' | |
- // doesn't match specified MPI_Datatype | |
-</pre> | |
-</blockquote> | |
-</li> | |
- | |
-<li><tt>must_be_null</tt> specifies that the expression should be a null | |
-pointer constant, for example: | |
- | |
-<blockquote> | |
-<pre> | |
-/* In mpi.h */ | |
-extern struct mpi_datatype mpi_datatype_null | |
- __attribute__(( type_tag_for_datatype(mpi, void, must_be_null) )); | |
- | |
-#define MPI_DATATYPE_NULL ((MPI_Datatype) &mpi_datatype_null) | |
- | |
-/* In user code */ | |
-MPI_Send(buffer, 1, MPI_DATATYPE_NULL /*, ... */); // warning: MPI_DATATYPE_NULL | |
- // was specified but buffer | |
- // is not a null pointer | |
-</pre> | |
-</blockquote> | |
-</li> | |
-</ul> | |
- | |
-</div> | |
-</body> | |
-</html> | |
Index: docs/ThreadSanitizer.rst | |
=================================================================== | |
--- docs/ThreadSanitizer.rst (revision 0) | |
+++ docs/ThreadSanitizer.rst (working copy) | |
@@ -0,0 +1,95 @@ | |
+ThreadSanitizer | |
+=============== | |
+ | |
+Introduction | |
+------------ | |
+ | |
+ThreadSanitizer is a tool that detects data races. It consists of a compiler | |
+instrumentation module and a run-time library. Typical slowdown introduced by | |
+ThreadSanitizer is **5x-15x** (TODO: these numbers are approximate so far). | |
+ | |
+How to build | |
+------------ | |
+ | |
+Follow the `Clang build instructions <../get_started.html>`_. CMake build is | |
+supported. | |
+ | |
+Supported Platforms | |
+------------------- | |
+ | |
+ThreadSanitizer is supported on Linux x86_64 (tested on Ubuntu 10.04). Support | |
+for MacOS 10.7 (64-bit only) is planned for late 2012. Support for 32-bit | |
+platforms is problematic and not yet planned. | |
+ | |
+Usage | |
+----- | |
+ | |
+Simply compile your program with ``-fsanitize=thread -fPIE`` and link it with | |
+``-fsanitize=thread -pie``. To get a reasonable performance add ``-O1`` or | |
+higher. Use ``-g`` to get file names and line numbers in the warning messages. | |
+ | |
+Example: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ % cat projects/compiler-rt/lib/tsan/output_tests/tiny_race.c | |
+ #include <pthread.h> | |
+ int Global; | |
+ void *Thread1(void *x) { | |
+ Global = 42; | |
+ return x; | |
+ } | |
+ int main() { | |
+ pthread_t t; | |
+ pthread_create(&t, NULL, Thread1, NULL); | |
+ Global = 43; | |
+ pthread_join(t, NULL); | |
+ return Global; | |
+ } | |
+ | |
+ $ clang -fsanitize=thread -g -O1 tiny_race.c -fPIE -pie | |
+ | |
+If a bug is detected, the program will print an error message to stderr. | |
+Currently, ThreadSanitizer symbolizes its output using an external | |
+``addr2line`` process (this will be fixed in future). | |
+ | |
+.. code-block:: bash | |
+ | |
+ % TSAN_OPTIONS=strip_path_prefix=`pwd`/ # Don't print full paths. | |
+ % ./a.out 2> log | |
+ % cat log | |
+ WARNING: ThreadSanitizer: data race (pid=19219) | |
+ Write of size 4 at 0x7fcf47b21bc0 by thread 1: | |
+ #0 Thread1 tiny_race.c:4 (exe+0x00000000a360) | |
+ Previous write of size 4 at 0x7fcf47b21bc0 by main thread: | |
+ #0 main tiny_race.c:10 (exe+0x00000000a3b4) | |
+ Thread 1 (running) created at: | |
+ #0 pthread_create ??:0 (exe+0x00000000c790) | |
+ #1 main tiny_race.c:9 (exe+0x00000000a3a4) | |
+ | |
+Limitations | |
+----------- | |
+ | |
+* ThreadSanitizer uses more real memory than a native run. At the default | |
+ settings the memory overhead is 9x plus 9Mb per each thread. Settings with 5x | |
+ and 3x overhead (but less accurate analysis) are also available. | |
+* ThreadSanitizer maps (but does not reserve) a lot of virtual address space. | |
+ This means that tools like ``ulimit`` may not work as usually expected. | |
+* Static linking is not supported. | |
+* ThreadSanitizer requires ``-fPIE -pie``. | |
+ | |
+Current Status | |
+-------------- | |
+ | |
+ThreadSanitizer is in alpha stage. It is known to work on large C++ programs | |
+using pthreads, but we do not promise anything (yet). C++11 threading is not | |
+yet supported. The test suite is integrated into CMake build and can be run | |
+with ``make check-tsan`` command. | |
+ | |
+We are actively working on enhancing the tool --- stay tuned. Any help, | |
+especially in the form of minimized standalone tests is more than welcome. | |
+ | |
+More Information | |
+---------------- | |
+`http://code.google.com/p/thread-sanitizer <http://code.google.com/p/thread-sanitizer/>`_. | |
+ | |
Index: docs/LibTooling.rst | |
=================================================================== | |
--- docs/LibTooling.rst (revision 0) | |
+++ docs/LibTooling.rst (working copy) | |
@@ -0,0 +1,206 @@ | |
+========== | |
+LibTooling | |
+========== | |
+ | |
+LibTooling is a library to support writing standalone tools based on Clang. | |
+This document will provide a basic walkthrough of how to write a tool using | |
+LibTooling. | |
+ | |
+For the information on how to setup Clang Tooling for LLVM see | |
+`HowToSetupToolingForLLVM.html <HowToSetupToolingForLLVM.html>`_ | |
+ | |
+Introduction | |
+------------ | |
+ | |
+Tools built with LibTooling, like Clang Plugins, run ``FrontendActions`` over | |
+code. | |
+ | |
+.. See FIXME for a tutorial on how to write FrontendActions. | |
+ | |
+In this tutorial, we'll demonstrate the different ways of running Clang's | |
+``SyntaxOnlyAction``, which runs a quick syntax check, over a bunch of code. | |
+ | |
+Parsing a code snippet in memory | |
+-------------------------------- | |
+ | |
+If you ever wanted to run a ``FrontendAction`` over some sample code, for | |
+example to unit test parts of the Clang AST, ``runToolOnCode`` is what you | |
+looked for. Let me give you an example: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ #include "clang/Tooling/Tooling.h" | |
+ | |
+ TEST(runToolOnCode, CanSyntaxCheckCode) { | |
+ // runToolOnCode returns whether the action was correctly run over the | |
+ // given code. | |
+ EXPECT_TRUE(runToolOnCode(new clang::SyntaxOnlyAction, "class X {};")); | |
+ } | |
+ | |
+Writing a standalone tool | |
+------------------------- | |
+ | |
+Once you unit tested your ``FrontendAction`` to the point where it cannot | |
+possibly break, it's time to create a standalone tool. For a standalone tool | |
+to run clang, it first needs to figure out what command line arguments to use | |
+for a specified file. To that end we create a ``CompilationDatabase``. There | |
+are different ways to create a compilation database, and we need to support all | |
+of them depending on command-line options. There's the ``CommonOptionsParser`` | |
+class that takes the responsibility to parse command-line parameters related to | |
+compilation databases and inputs, so that all tools share the implementation. | |
+ | |
+Parsing common tools options | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+``CompilationDatabase`` can be read from a build directory or the command line. | |
+Using ``CommonOptionsParser`` allows for explicit specification of a compile | |
+command line, specification of build path using the ``-p`` command-line option, | |
+and automatic location of the compilation database using source files paths. | |
+ | |
+.. code-block:: c++ | |
+ | |
+ #include "clang/Tooling/CommonOptionsParser.h" | |
+ | |
+ using namespace clang::tooling; | |
+ | |
+ int main(int argc, const char **argv) { | |
+ // CommonOptionsParser constructor will parse arguments and create a | |
+ // CompilationDatabase. In case of error it will terminate the program. | |
+ CommonOptionsParser OptionsParser(argc, argv); | |
+ | |
+ // Use OptionsParser.GetCompilations() and OptionsParser.GetSourcePathList() | |
+ // to retrieve CompilationDatabase and the list of input file paths. | |
+ } | |
+ | |
+Creating and running a ClangTool | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Once we have a ``CompilationDatabase``, we can create a ``ClangTool`` and run | |
+our ``FrontendAction`` over some code. For example, to run the | |
+``SyntaxOnlyAction`` over the files "a.cc" and "b.cc" one would write: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ // A clang tool can run over a number of sources in the same process... | |
+ std::vector<std::string> Sources; | |
+ Sources.push_back("a.cc"); | |
+ Sources.push_back("b.cc"); | |
+ | |
+ // We hand the CompilationDatabase we created and the sources to run over into | |
+ // the tool constructor. | |
+ ClangTool Tool(OptionsParser.GetCompilations(), Sources); | |
+ | |
+ // The ClangTool needs a new FrontendAction for each translation unit we run | |
+ // on. Thus, it takes a FrontendActionFactory as parameter. To create a | |
+ // FrontendActionFactory from a given FrontendAction type, we call | |
+ // newFrontendActionFactory<clang::SyntaxOnlyAction>(). | |
+ int result = Tool.run(newFrontendActionFactory<clang::SyntaxOnlyAction>()); | |
+ | |
+Putting it together --- the first tool | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Now we combine the two previous steps into our first real tool. This example | |
+tool is also checked into the clang tree at | |
+``tools/clang-check/ClangCheck.cpp``. | |
+ | |
+.. code-block:: c++ | |
+ | |
+ // Declares clang::SyntaxOnlyAction. | |
+ #include "clang/Frontend/FrontendActions.h" | |
+ #include "clang/Tooling/CommonOptionsParser.h" | |
+ #include "clang/Tooling/Tooling.h" | |
+ // Declares llvm::cl::extrahelp. | |
+ #include "llvm/Support/CommandLine.h" | |
+ | |
+ using namespace clang::tooling; | |
+ using namespace llvm; | |
+ | |
+ // CommonOptionsParser declares HelpMessage with a description of the common | |
+ // command-line options related to the compilation database and input files. | |
+ // It's nice to have this help message in all tools. | |
+ static cl::extrahelp CommonHelp(CommonOptionsParser::HelpMessage); | |
+ | |
+ // A help message for this specific tool can be added afterwards. | |
+ static cl::extrahelp MoreHelp("\nMore help text..."); | |
+ | |
+ int main(int argc, const char **argv) { | |
+ CommonOptionsParser OptionsParser(argc, argv); | |
+ ClangTool Tool(OptionsParser.GetCompilations(), | |
+ OptionsParser.GetSourcePathList()); | |
+ return Tool.run(newFrontendActionFactory<clang::SyntaxOnlyAction>()); | |
+ } | |
+ | |
+Running the tool on some code | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+When you check out and build clang, clang-check is already built and available | |
+to you in bin/clang-check inside your build directory. | |
+ | |
+You can run clang-check on a file in the llvm repository by specifying all the | |
+needed parameters after a "``--``" separator: | |
+ | |
+.. code-block:: bash | |
+ | |
+ $ cd /path/to/source/llvm | |
+ $ export BD=/path/to/build/llvm | |
+ $ $BD/bin/clang-check tools/clang/tools/clang-check/ClangCheck.cpp -- \ | |
+ clang++ -D__STDC_CONSTANT_MACROS -D__STDC_LIMIT_MACROS \ | |
+ -Itools/clang/include -I$BD/include -Iinclude \ | |
+ -Itools/clang/lib/Headers -c | |
+ | |
+As an alternative, you can also configure cmake to output a compile command | |
+database into its build directory: | |
+ | |
+.. code-block:: bash | |
+ | |
+ # Alternatively to calling cmake, use ccmake, toggle to advanced mode and | |
+ # set the parameter CMAKE_EXPORT_COMPILE_COMMANDS from the UI. | |
+ $ cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=ON . | |
+ | |
+This creates a file called ``compile_commands.json`` in the build directory. | |
+Now you can run :program:`clang-check` over files in the project by specifying | |
+the build path as first argument and some source files as further positional | |
+arguments: | |
+ | |
+.. code-block:: bash | |
+ | |
+ $ cd /path/to/source/llvm | |
+ $ export BD=/path/to/build/llvm | |
+ $ $BD/bin/clang-check -p $BD tools/clang/tools/clang-check/ClangCheck.cpp | |
+ | |
+Builtin includes | |
+^^^^^^^^^^^^^^^^ | |
+ | |
+Clang tools need their builtin headers and search for them the same way Clang | |
+does. Thus, the default location to look for builtin headers is in a path | |
+``$(dirname /path/to/tool)/../lib/clang/3.2/include`` relative to the tool | |
+binary. This works out-of-the-box for tools running from llvm's toplevel | |
+binary directory after building clang-headers, or if the tool is running from | |
+the binary directory of a clang install next to the clang binary. | |
+ | |
+Tips: if your tool fails to find ``stddef.h`` or similar headers, call the tool | |
+with ``-v`` and look at the search paths it looks through. | |
+ | |
+Linking | |
+^^^^^^^ | |
+ | |
+Please note that this presents the linking requirements at the time of this | |
+writing. For the most up-to-date information, look at one of the tools' | |
+Makefiles (for example `clang-check/Makefile | |
+<http://llvm.org/viewvc/llvm-project/cfe/trunk/tools/clang-check/Makefile?view=markup>`_). | |
+ | |
+To link a binary using the tooling infrastructure, link in the following | |
+libraries: | |
+ | |
+* Tooling | |
+* Frontend | |
+* Driver | |
+* Serialization | |
+* Parse | |
+* Sema | |
+* Analysis | |
+* Edit | |
+* AST | |
+* Lex | |
+* Basic | |
+ | |
Index: docs/Tooling.rst | |
=================================================================== | |
--- docs/Tooling.rst (revision 0) | |
+++ docs/Tooling.rst (working copy) | |
@@ -0,0 +1,100 @@ | |
+=================== | |
+Writing Clang Tools | |
+=================== | |
+ | |
+Clang provides infrastructure to write tools that need syntactic and semantic | |
+information about a program. This document will give a short introduction of | |
+the different ways to write clang tools, and their pros and cons. | |
+ | |
+LibClang | |
+-------- | |
+ | |
+`LibClang <http://clang.llvm.org/doxygen/group__CINDEX.html>`_ is a stable high | |
+level C interface to clang. When in doubt LibClang is probably the interface | |
+you want to use. Consider the other interfaces only when you have a good | |
+reason not to use LibClang. | |
+ | |
+Canonical examples of when to use LibClang: | |
+ | |
+* Xcode | |
+* Clang Python Bindings | |
+ | |
+Use LibClang when you...: | |
+ | |
+* want to interface with clang from other languages than C++ | |
+* need a stable interface that takes care to be backwards compatible | |
+* want powerful high-level abstractions, like iterating through an AST with a | |
+ cursor, and don't want to learn all the nitty gritty details of Clang's AST. | |
+ | |
+Do not use LibClang when you...: | |
+ | |
+* want full control over the Clang AST | |
+ | |
+Clang Plugins | |
+------------- | |
+ | |
+`Clang Plugins <ClangPlugins.html>`_ allow you to run additional actions on the | |
+AST as part of a compilation. Plugins are dynamic libraries that are loaded at | |
+runtime by the compiler, and they're easy to integrate into your build | |
+environment. | |
+ | |
+Canonical examples of when to use Clang Plugins: | |
+ | |
+* special lint-style warnings or errors for your project | |
+* creating additional build artifacts from a single compile step | |
+ | |
+Use Clang Plugins when you...: | |
+ | |
+* need your tool to rerun if any of the dependencies change | |
+* want your tool to make or break a build | |
+* need full control over the Clang AST | |
+ | |
+Do not use Clang Plugins when you...: | |
+ | |
+* want to run tools outside of your build environment | |
+* want full control on how Clang is set up, including mapping of in-memory | |
+ virtual files | |
+* need to run over a specific subset of files in your project which is not | |
+ necessarily related to any changes which would trigger rebuilds | |
+ | |
+LibTooling | |
+---------- | |
+ | |
+`LibTooling <LibTooling.html>`_ is a C++ interface aimed at writing standalone | |
+tools, as well as integrating into services that run clang tools. Canonical | |
+examples of when to use LibTooling: | |
+ | |
+* a simple syntax checker | |
+* refactoring tools | |
+ | |
+Use LibTooling when you...: | |
+ | |
+* want to run tools over a single file, or a specific subset of files, | |
+ independently of the build system | |
+* want full control over the Clang AST | |
+* want to share code with Clang Plgins | |
+ | |
+Do not use LibTooling when you...: | |
+ | |
+* want to run as part of the build triggered by dependency changes | |
+* want a stable interface so you don't need to change your code when the AST API | |
+ changes | |
+* want high level abstractions like cursors and code completion out of the box | |
+* do not want to write your tools in C++ | |
+ | |
+Clang Tools | |
+----------- | |
+ | |
+`Clang tools <ClangTools.html>`_ are a collection of specific developer tools | |
+built on top of the LibTooling infrastructure as part of the Clang project. | |
+They are targeted at automating and improving core development activities of | |
+C/C++ developers. | |
+ | |
+Examples of tools we are building or planning as part of the Clang project: | |
+ | |
+* Syntax checking (:program:`clang-check`) | |
+* Automatic fixing of compile errors (:program:`clang-fixit`) | |
+* Automatic code formatting | |
+* Migration tools for new features in new language standards | |
+* Core refactoring tools | |
+ | |
Index: docs/LibTooling.html | |
=================================================================== | |
--- docs/LibTooling.html (revision 169710) | |
+++ docs/LibTooling.html (working copy) | |
@@ -1,212 +0,0 @@ | |
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" | |
- "http://www.w3.org/TR/html4/strict.dtd"> | |
-<html> | |
-<head> | |
-<title>LibTooling</title> | |
-<link type="text/css" rel="stylesheet" href="../menu.css"> | |
-<link type="text/css" rel="stylesheet" href="../content.css"> | |
-</head> | |
-<body> | |
- | |
-<!--#include virtual="../menu.html.incl"--> | |
- | |
-<div id="content"> | |
- | |
-<h1>LibTooling</h1> | |
-<p>LibTooling is a library to support writing standalone tools based on | |
-Clang. This document will provide a basic walkthrough of how to write | |
-a tool using LibTooling.</p> | |
-<p>For the information on how to setup Clang Tooling for LLVM see | |
-<a href="HowToSetupToolingForLLVM.html">HowToSetupToolingForLLVM.html</a></p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="intro">Introduction</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Tools built with LibTooling, like Clang Plugins, run | |
-<code>FrontendActions</code> over code. | |
-<!-- See FIXME for a tutorial on how to write FrontendActions. --> | |
-In this tutorial, we'll demonstrate the different ways of running clang's | |
-<code>SyntaxOnlyAction</code>, which runs a quick syntax check, over a bunch of | |
-code.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="runoncode">Parsing a code snippet in memory.</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>If you ever wanted to run a <code>FrontendAction</code> over some sample | |
-code, for example to unit test parts of the Clang AST, | |
-<code>runToolOnCode</code> is what you looked for. Let me give you an example: | |
-<pre> | |
- #include "clang/Tooling/Tooling.h" | |
- | |
- TEST(runToolOnCode, CanSyntaxCheckCode) { | |
- // runToolOnCode returns whether the action was correctly run over the | |
- // given code. | |
- EXPECT_TRUE(runToolOnCode(new clang::SyntaxOnlyAction, "class X {};")); | |
- } | |
-</pre> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="standalonetool">Writing a standalone tool.</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Once you unit tested your <code>FrontendAction</code> to the point where it | |
-cannot possibly break, it's time to create a standalone tool. For a standalone | |
-tool to run clang, it first needs to figure out what command line arguments to | |
-use for a specified file. To that end we create a | |
-<code>CompilationDatabase</code>. There are different ways to create a | |
-compilation database, and we need to support all of them depending on | |
-command-line options. There's the <code>CommonOptionsParser</code> class | |
-that takes the responsibility to parse command-line parameters related to | |
-compilation databases and inputs, so that all tools share the implementation. | |
-</p> | |
- | |
-<h3 id="parsingcommonoptions">Parsing common tools options.</h3> | |
-<p><code>CompilationDatabase</code> can be read from a build directory or the | |
-command line. Using <code>CommonOptionsParser</code> allows for explicit | |
-specification of a compile command line, specification of build path using the | |
-<code>-p</code> command-line option, and automatic location of the compilation | |
-database using source files paths. | |
-<pre> | |
-#include "clang/Tooling/CommonOptionsParser.h" | |
- | |
-using namespace clang::tooling; | |
- | |
-int main(int argc, const char **argv) { | |
- // CommonOptionsParser constructor will parse arguments and create a | |
- // CompilationDatabase. In case of error it will terminate the program. | |
- CommonOptionsParser OptionsParser(argc, argv); | |
- | |
- // Use OptionsParser.GetCompilations() and OptionsParser.GetSourcePathList() | |
- // to retrieve CompilationDatabase and the list of input file paths. | |
-} | |
-</pre> | |
-</p> | |
- | |
-<h3 id="tool">Creating and running a ClangTool.</h3> | |
-<p>Once we have a <code>CompilationDatabase</code>, we can create a | |
-<code>ClangTool</code> and run our <code>FrontendAction</code> over some code. | |
-For example, to run the <code>SyntaxOnlyAction</code> over the files "a.cc" and | |
-"b.cc" one would write: | |
-<pre> | |
- // A clang tool can run over a number of sources in the same process... | |
- std::vector<std::string> Sources; | |
- Sources.push_back("a.cc"); | |
- Sources.push_back("b.cc"); | |
- | |
- // We hand the CompilationDatabase we created and the sources to run over into | |
- // the tool constructor. | |
- ClangTool Tool(OptionsParser.GetCompilations(), Sources); | |
- | |
- // The ClangTool needs a new FrontendAction for each translation unit we run | |
- // on. Thus, it takes a FrontendActionFactory as parameter. To create a | |
- // FrontendActionFactory from a given FrontendAction type, we call | |
- // newFrontendActionFactory<clang::SyntaxOnlyAction>(). | |
- int result = Tool.run(newFrontendActionFactory<clang::SyntaxOnlyAction>()); | |
-</pre> | |
-</p> | |
- | |
-<h3 id="main">Putting it together - the first tool.</h3> | |
-<p>Now we combine the two previous steps into our first real tool. This example | |
-tool is also checked into the clang tree at tools/clang-check/ClangCheck.cpp. | |
-<pre> | |
-// Declares clang::SyntaxOnlyAction. | |
-#include "clang/Frontend/FrontendActions.h" | |
-#include "clang/Tooling/CommonOptionsParser.h" | |
-#include "clang/Tooling/Tooling.h" | |
-// Declares llvm::cl::extrahelp. | |
-#include "llvm/Support/CommandLine.h" | |
- | |
-using namespace clang::tooling; | |
-using namespace llvm; | |
- | |
-// CommonOptionsParser declares HelpMessage with a description of the common | |
-// command-line options related to the compilation database and input files. | |
-// It's nice to have this help message in all tools. | |
-static cl::extrahelp CommonHelp(CommonOptionsParser::HelpMessage); | |
- | |
-// A help message for this specific tool can be added afterwards. | |
-static cl::extrahelp MoreHelp("\nMore help text..."); | |
- | |
-int main(int argc, const char **argv) { | |
- CommonOptionsParser OptionsParser(argc, argv); | |
- ClangTool Tool(OptionsParser.GetCompilations(), | |
- OptionsParser.GetSourcePathList()); | |
- return Tool.run(newFrontendActionFactory<clang::SyntaxOnlyAction>()); | |
-} | |
-</pre> | |
-</p> | |
- | |
-<h3 id="running">Running the tool on some code.</h3> | |
-<p>When you check out and build clang, clang-check is already built and | |
-available to you in bin/clang-check inside your build directory.</p> | |
-<p>You can run clang-check on a file in the llvm repository by specifying | |
-all the needed parameters after a "--" separator: | |
-<pre> | |
- $ cd /path/to/source/llvm | |
- $ export BD=/path/to/build/llvm | |
- $ $BD/bin/clang-check tools/clang/tools/clang-check/ClangCheck.cpp -- \ | |
- clang++ -D__STDC_CONSTANT_MACROS -D__STDC_LIMIT_MACROS \ | |
- -Itools/clang/include -I$BD/include -Iinclude -Itools/clang/lib/Headers -c | |
-</pre> | |
-</p> | |
- | |
-<p>As an alternative, you can also configure cmake to output a compile command | |
-database into its build directory: | |
-<pre> | |
- # Alternatively to calling cmake, use ccmake, toggle to advanced mode and | |
- # set the parameter CMAKE_EXPORT_COMPILE_COMMANDS from the UI. | |
- $ cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=ON . | |
-</pre> | |
-</p> | |
-<p> | |
-This creates a file called compile_commands.json in the build directory. Now | |
-you can run clang-check over files in the project by specifying the build path | |
-as first argument and some source files as further positional arguments: | |
-<pre> | |
- $ cd /path/to/source/llvm | |
- $ export BD=/path/to/build/llvm | |
- $ $BD/bin/clang-check -p $BD tools/clang/tools/clang-check/ClangCheck.cpp | |
-</pre> | |
-</p> | |
- | |
-<h3 id="builtin">Builtin includes.</h3> | |
-<p>Clang tools need their builtin headers and search for them the same way clang | |
-does. Thus, the default location to look for builtin headers is in a path | |
-$(dirname /path/to/tool)/../lib/clang/3.2/include relative to the tool | |
-binary. This works out-of-the-box for tools running from llvm's toplevel | |
-binary directory after building clang-headers, or if the tool is running | |
-from the binary directory of a clang install next to the clang binary.</p> | |
- | |
-<p>Tips: if your tool fails to find stddef.h or similar headers, call | |
-the tool with -v and look at the search paths it looks through.</p> | |
- | |
-<h3 id="linking">Linking.</h3> | |
-<p>Please note that this presents the linking requirements at the time of this | |
-writing. For the most up-to-date information, look at one of the tools' | |
-Makefiles (for example | |
-<a href="http://llvm.org/viewvc/llvm-project/cfe/trunk/tools/clang-check/Makefile?view=markup">clang-check/Makefile</a>). | |
-</p> | |
- | |
-<p>To link a binary using the tooling infrastructure, link in the following | |
-libraries: | |
-<ul> | |
-<li>Tooling</li> | |
-<li>Frontend</li> | |
-<li>Driver</li> | |
-<li>Serialization</li> | |
-<li>Parse</li> | |
-<li>Sema</li> | |
-<li>Analysis</li> | |
-<li>Edit</li> | |
-<li>AST</li> | |
-<li>Lex</li> | |
-<li>Basic</li> | |
-</ul> | |
-</p> | |
- | |
-</div> | |
-</body> | |
-</html> | |
- | |
Index: docs/LibASTMatchers.html | |
=================================================================== | |
--- docs/LibASTMatchers.html (revision 169710) | |
+++ docs/LibASTMatchers.html (working copy) | |
@@ -1,130 +0,0 @@ | |
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" | |
- "http://www.w3.org/TR/html4/strict.dtd"> | |
-<html> | |
-<head> | |
-<title>Matching the Clang AST</title> | |
-<link type="text/css" rel="stylesheet" href="../menu.css" /> | |
-<link type="text/css" rel="stylesheet" href="../content.css" /> | |
-</head> | |
-<body> | |
- | |
-<!--#include virtual="../menu.html.incl"--> | |
- | |
-<div id="content"> | |
- | |
-<h1>Matching the Clang AST</h1> | |
-<p>This document explains how to use Clang's LibASTMatchers to match interesting | |
-nodes of the AST and execute code that uses the matched nodes. Combined with | |
-<a href="LibTooling.html">LibTooling</a>, LibASTMatchers helps to write | |
-code-to-code transformation tools or query tools.</p> | |
- | |
-<p>We assume basic knowledge about the Clang AST. See the | |
-<a href="IntroductionToTheClangAST.html">Introduction to the Clang AST</a> if | |
-you want to learn more about how the AST is structured.</p> | |
- | |
-<!-- FIXME: create tutorial and link to the tutorial --> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="intro">Introduction</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>LibASTMatchers provides a domain specific language to create predicates on Clang's | |
-AST. This DSL is written in and can be used from C++, allowing users to write | |
-a single program to both match AST nodes and access the node's C++ interface | |
-to extract attributes, source locations, or any other information provided on | |
-the AST level.</p> | |
- | |
-<p>AST matchers are predicates on nodes in the AST. Matchers are created | |
-by calling creator functions that allow building up a tree of matchers, where | |
-inner matchers are used to make the match more specific.</p> | |
- | |
-</p>For example, to create a matcher that matches all class or union declarations | |
-in the AST of a translation unit, you can call | |
-<a href="LibASTMatchersReference.html#recordDecl0Anchor">recordDecl()</a>. | |
-To narrow the match down, for example to find all class or union declarations with the name "Foo", | |
-insert a <a href="LibASTMatchersReference.html#hasName0Anchor">hasName</a> | |
-matcher: the call recordDecl(hasName("Foo")) returns a matcher that matches classes | |
-or unions that are named "Foo", in any namespace. By default, matchers that accept | |
-multiple inner matchers use an implicit <a href="LibASTMatchersReference.html#allOf0Anchor">allOf()</a>. | |
-This allows further narrowing down the match, for example to match all classes | |
-that are derived from "Bar": recordDecl(hasName("Foo"), isDerivedFrom("Bar")).</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="writing">How to create a matcher</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>With more than a thousand classes in the Clang AST, one can quickly get lost | |
-when trying to figure out how to create a matcher for a specific pattern. This | |
-section will teach you how to use a rigorous step-by-step pattern to build the | |
-matcher you are interested in. Note that there will always be matchers missing | |
-for some part of the AST. See the section about <a href="#writing">how to write | |
-your own AST matchers</a> later in this document.</p> | |
- | |
-<p>The precondition to using the matchers is to understand how the AST | |
-for what you want to match looks like. The <a href="IntroductionToTheClangAST.html">Introduction to the Clang AST</a> | |
-teaches you how to dump a translation unit's AST into a human readable format.</p> | |
- | |
-<!-- FIXME: Introduce link to ASTMatchersTutorial.html --> | |
-<!-- FIXME: Introduce link to ASTMatchersCookbook.html --> | |
- | |
-<p>In general, the strategy to create the right matchers is:</p> | |
-<ol> | |
-<li>Find the outermost class in Clang's AST you want to match.</li> | |
-<li>Look at the <a href="LibASTMatchersReference.html">AST Matcher Reference</a> for matchers that either match the | |
-node you're interested in or narrow down attributes on the node.</li> | |
-<li>Create your outer match expression. Verify that it works as expected.</li> | |
-<li>Examine the matchers for what the next inner node you want to match is.</li> | |
-<li>Repeat until the matcher is finished.</li> | |
-</ol> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="binding">Binding nodes in match expressions</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Matcher expressions allow you to specify which parts of the AST are interesting | |
-for a certain task. Often you will want to then do something with the nodes | |
-that were matched, like building source code transformations.</p> | |
- | |
-<p>To that end, matchers that match specific AST nodes (so called node matchers) | |
-are bindable; for example, recordDecl(hasName("MyClass")).bind("id") will bind | |
-the matched recordDecl node to the string "id", to be later retrieved in the | |
-<a href="http://clang.llvm.org/doxygen/classclang_1_1ast__matchers_1_1MatchFinder_1_1MatchCallback.html">match callback</a>.</p> | |
- | |
-<!-- FIXME: Introduce link to ASTMatchersTutorial.html --> | |
-<!-- FIXME: Introduce link to ASTMatchersCookbook.html --> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="writing">Writing your own matchers</h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>There are multiple different ways to define a matcher, depending on its | |
-type and flexibility.</p> | |
-<ul> | |
-<li><b>VariadicDynCastAllOfMatcher<Base, Derived></b><p>Those match all nodes | |
-of type <i>Base</i> if they can be dynamically casted to <i>Derived</i>. The | |
-names of those matchers are nouns, which closely resemble <i>Derived</i>. | |
-VariadicDynCastAllOfMatchers are the backbone of the matcher hierarchy. Most | |
-often, your match expression will start with one of them, and you can | |
-<a href="#binding">bind</a> the node they represent to ids for later processing.</p> | |
-<p>VariadicDynCastAllOfMatchers are callable classes that model variadic | |
-template functions in C++03. They take an aribtrary number of Matcher<Derived> | |
-and return a Matcher<Base>.</p></li> | |
-<li><b>AST_MATCHER_P(Type, Name, ParamType, Param)</b><p> Most matcher definitions | |
-use the matcher creation macros. Those define both the matcher of type Matcher<Type> | |
-itself, and a matcher-creation function named <i>Name</i> that takes a parameter | |
-of type <i>ParamType</i> and returns the corresponding matcher.</p> | |
-<p>There are multiple matcher definition macros that deal with polymorphic return | |
-values and different parameter counts. See <a href="http://clang.llvm.org/doxygen/ASTMatchersMacros_8h.html">ASTMatchersMacros.h</a>. | |
-</p></li> | |
-<li><b>Matcher creation functions</b><p>Matchers are generated by nesting | |
-calls to matcher creation functions. Most of the time those functions are either | |
-created by using VariadicDynCastAllOfMatcher or the matcher creation macros | |
-(see below). The free-standing functions are an indication that this matcher | |
-is just a combination of other matchers, as is for example the case with | |
-<a href="LibASTMatchersReference.html#callee1Anchor">callee</a>.</p></li> | |
-</ul> | |
- | |
-</div> | |
-</body> | |
-</html> | |
- | |
Index: docs/LibASTMatchers.rst | |
=================================================================== | |
--- docs/LibASTMatchers.rst (revision 0) | |
+++ docs/LibASTMatchers.rst (working copy) | |
@@ -0,0 +1,134 @@ | |
+====================== | |
+Matching the Clang AST | |
+====================== | |
+ | |
+This document explains how to use Clang's LibASTMatchers to match interesting | |
+nodes of the AST and execute code that uses the matched nodes. Combined with | |
+:doc:`LibTooling`, LibASTMatchers helps to write code-to-code transformation | |
+tools or query tools. | |
+ | |
+We assume basic knowledge about the Clang AST. See the `Introduction to the | |
+Clang AST <IntroductionToTheClangAST.html>`_ if you want to learn more about | |
+how the AST is structured. | |
+ | |
+.. FIXME: create tutorial and link to the tutorial | |
+ | |
+Introduction | |
+------------ | |
+ | |
+LibASTMatchers provides a domain specific language to create predicates on | |
+Clang's AST. This DSL is written in and can be used from C++, allowing users | |
+to write a single program to both match AST nodes and access the node's C++ | |
+interface to extract attributes, source locations, or any other information | |
+provided on the AST level. | |
+ | |
+AST matchers are predicates on nodes in the AST. Matchers are created by | |
+calling creator functions that allow building up a tree of matchers, where | |
+inner matchers are used to make the match more specific. | |
+ | |
+For example, to create a matcher that matches all class or union declarations | |
+in the AST of a translation unit, you can call `recordDecl() | |
+<LibASTMatchersReference.html#recordDecl0Anchor>`_. To narrow the match down, | |
+for example to find all class or union declarations with the name "``Foo``", | |
+insert a `hasName <LibASTMatchersReference.html#hasName0Anchor>`_ matcher: the | |
+call ``recordDecl(hasName("Foo"))`` returns a matcher that matches classes or | |
+unions that are named "``Foo``", in any namespace. By default, matchers that | |
+accept multiple inner matchers use an implicit `allOf() | |
+<LibASTMatchersReference.html#allOf0Anchor>`_. This allows further narrowing | |
+down the match, for example to match all classes that are derived from | |
+"``Bar``": ``recordDecl(hasName("Foo"), isDerivedFrom("Bar"))``. | |
+ | |
+.. _astmatchers-writing: | |
+ | |
+How to create a matcher | |
+----------------------- | |
+ | |
+With more than a thousand classes in the Clang AST, one can quickly get lost | |
+when trying to figure out how to create a matcher for a specific pattern. This | |
+section will teach you how to use a rigorous step-by-step pattern to build the | |
+matcher you are interested in. Note that there will always be matchers missing | |
+for some part of the AST. See the section about :ref:`how to write your own | |
+AST matchers <astmatchers-writing>` later in this document. | |
+ | |
+.. FIXME: why is it linking back to the same section?! | |
+ | |
+The precondition to using the matchers is to understand how the AST for what you | |
+want to match looks like. The | |
+`Introduction to the Clang AST <IntroductionToTheClangAST.html>`_ teaches you | |
+how to dump a translation unit's AST into a human readable format. | |
+ | |
+.. FIXME: Introduce link to ASTMatchersTutorial.html | |
+.. FIXME: Introduce link to ASTMatchersCookbook.html | |
+ | |
+In general, the strategy to create the right matchers is: | |
+ | |
+#. Find the outermost class in Clang's AST you want to match. | |
+#. Look at the `AST Matcher Reference <LibASTMatchersReference.html>`_ for | |
+ matchers that either match the node you're interested in or narrow down | |
+ attributes on the node. | |
+#. Create your outer match expression. Verify that it works as expected. | |
+#. Examine the matchers for what the next inner node you want to match is. | |
+#. Repeat until the matcher is finished. | |
+ | |
+.. _astmatchers-bind: | |
+ | |
+Binding nodes in match expressions | |
+---------------------------------- | |
+ | |
+Matcher expressions allow you to specify which parts of the AST are interesting | |
+for a certain task. Often you will want to then do something with the nodes | |
+that were matched, like building source code transformations. | |
+ | |
+To that end, matchers that match specific AST nodes (so called node matchers) | |
+are bindable; for example, ``recordDecl(hasName("MyClass")).bind("id")`` will | |
+bind the matched ``recordDecl`` node to the string "``id``", to be later | |
+retrieved in the `match callback | |
+<http://clang.llvm.org/doxygen/classclang_1_1ast__matchers_1_1MatchFinder_1_1MatchCallback.html>`_. | |
+ | |
+.. FIXME: Introduce link to ASTMatchersTutorial.html | |
+.. FIXME: Introduce link to ASTMatchersCookbook.html | |
+ | |
+Writing your own matchers | |
+------------------------- | |
+ | |
+There are multiple different ways to define a matcher, depending on its type | |
+and flexibility. | |
+ | |
+``VariadicDynCastAllOfMatcher<Base, Derived>`` | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Those match all nodes of type *Base* if they can be dynamically casted to | |
+*Derived*. The names of those matchers are nouns, which closely resemble | |
+*Derived*. ``VariadicDynCastAllOfMatchers`` are the backbone of the matcher | |
+hierarchy. Most often, your match expression will start with one of them, and | |
+you can :ref:`bind <astmatchers-bind>` the node they represent to ids for later | |
+processing. | |
+ | |
+``VariadicDynCastAllOfMatchers`` are callable classes that model variadic | |
+template functions in C++03. They take an aribtrary number of | |
+``Matcher<Derived>`` and return a ``Matcher<Base>``. | |
+ | |
+``AST_MATCHER_P(Type, Name, ParamType, Param)`` | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Most matcher definitions use the matcher creation macros. Those define both | |
+the matcher of type ``Matcher<Type>`` itself, and a matcher-creation function | |
+named *Name* that takes a parameter of type *ParamType* and returns the | |
+corresponding matcher. | |
+ | |
+There are multiple matcher definition macros that deal with polymorphic return | |
+values and different parameter counts. See `ASTMatchersMacros.h | |
+<http://clang.llvm.org/doxygen/ASTMatchersMacros_8h.html>`_. | |
+ | |
+Matcher creation functions | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Matchers are generated by nesting calls to matcher creation functions. Most of | |
+the time those functions are either created by using | |
+``VariadicDynCastAllOfMatcher`` or the matcher creation macros (see below). | |
+The free-standing functions are an indication that this matcher is just a | |
+combination of other matchers, as is for example the case with `callee | |
+<LibASTMatchersReference.html#callee1Anchor>`_. | |
+ | |
+.. FIXME: "... macros (see below)" --- there isn't anything below | |
+ | |
Index: docs/LanguageExtensions.rst | |
=================================================================== | |
--- docs/LanguageExtensions.rst (revision 0) | |
+++ docs/LanguageExtensions.rst (working copy) | |
@@ -0,0 +1,1838 @@ | |
+========================= | |
+Clang Language Extensions | |
+========================= | |
+ | |
+.. contents:: | |
+ :local: | |
+ | |
+Introduction | |
+============ | |
+ | |
+This document describes the language extensions provided by Clang. In addition | |
+to the language extensions listed here, Clang aims to support a broad range of | |
+GCC extensions. Please see the `GCC manual | |
+<http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html>`_ for more information on | |
+these extensions. | |
+ | |
+.. _langext-feature_check: | |
+ | |
+Feature Checking Macros | |
+======================= | |
+ | |
+Language extensions can be very useful, but only if you know you can depend on | |
+them. In order to allow fine-grain features checks, we support three builtin | |
+function-like macros. This allows you to directly test for a feature in your | |
+code without having to resort to something like autoconf or fragile "compiler | |
+version checks". | |
+ | |
+``__has_builtin`` | |
+----------------- | |
+ | |
+This function-like macro takes a single identifier argument that is the name of | |
+a builtin function. It evaluates to 1 if the builtin is supported or 0 if not. | |
+It can be used like this: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ #ifndef __has_builtin // Optional of course. | |
+ #define __has_builtin(x) 0 // Compatibility with non-clang compilers. | |
+ #endif | |
+ | |
+ ... | |
+ #if __has_builtin(__builtin_trap) | |
+ __builtin_trap(); | |
+ #else | |
+ abort(); | |
+ #endif | |
+ ... | |
+ | |
+.. _langext-__has_feature-__has_extension: | |
+ | |
+``__has_feature`` and ``__has_extension`` | |
+----------------------------------------- | |
+ | |
+These function-like macros take a single identifier argument that is the name | |
+of a feature. ``__has_feature`` evaluates to 1 if the feature is both | |
+supported by Clang and standardized in the current language standard or 0 if | |
+not (but see :ref:`below <langext-has-feature-back-compat>`), while | |
+``__has_extension`` evaluates to 1 if the feature is supported by Clang in the | |
+current language (either as a language extension or a standard language | |
+feature) or 0 if not. They can be used like this: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ #ifndef __has_feature // Optional of course. | |
+ #define __has_feature(x) 0 // Compatibility with non-clang compilers. | |
+ #endif | |
+ #ifndef __has_extension | |
+ #define __has_extension __has_feature // Compatibility with pre-3.0 compilers. | |
+ #endif | |
+ | |
+ ... | |
+ #if __has_feature(cxx_rvalue_references) | |
+ // This code will only be compiled with the -std=c++11 and -std=gnu++11 | |
+ // options, because rvalue references are only standardized in C++11. | |
+ #endif | |
+ | |
+ #if __has_extension(cxx_rvalue_references) | |
+ // This code will be compiled with the -std=c++11, -std=gnu++11, -std=c++98 | |
+ // and -std=gnu++98 options, because rvalue references are supported as a | |
+ // language extension in C++98. | |
+ #endif | |
+ | |
+.. _langext-has-feature-back-compat: | |
+ | |
+For backwards compatibility reasons, ``__has_feature`` can also be used to test | |
+for support for non-standardized features, i.e. features not prefixed ``c_``, | |
+``cxx_`` or ``objc_``. | |
+ | |
+Another use of ``__has_feature`` is to check for compiler features not related | |
+to the language standard, such as e.g. `AddressSanitizer | |
+<AddressSanitizer.html>`_. | |
+ | |
+If the ``-pedantic-errors`` option is given, ``__has_extension`` is equivalent | |
+to ``__has_feature``. | |
+ | |
+The feature tag is described along with the language feature below. | |
+ | |
+The feature name or extension name can also be specified with a preceding and | |
+following ``__`` (double underscore) to avoid interference from a macro with | |
+the same name. For instance, ``__cxx_rvalue_references__`` can be used instead | |
+of ``cxx_rvalue_references``. | |
+ | |
+``__has_attribute`` | |
+------------------- | |
+ | |
+This function-like macro takes a single identifier argument that is the name of | |
+an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It | |
+can be used like this: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ #ifndef __has_attribute // Optional of course. | |
+ #define __has_attribute(x) 0 // Compatibility with non-clang compilers. | |
+ #endif | |
+ | |
+ ... | |
+ #if __has_attribute(always_inline) | |
+ #define ALWAYS_INLINE __attribute__((always_inline)) | |
+ #else | |
+ #define ALWAYS_INLINE | |
+ #endif | |
+ ... | |
+ | |
+The attribute name can also be specified with a preceding and following ``__`` | |
+(double underscore) to avoid interference from a macro with the same name. For | |
+instance, ``__always_inline__`` can be used instead of ``always_inline``. | |
+ | |
+Include File Checking Macros | |
+============================ | |
+ | |
+Not all developments systems have the same include files. The | |
+:ref:`langext-__has_include` and :ref:`langext-__has_include_next` macros allow | |
+you to check for the existence of an include file before doing a possibly | |
+failing ``#include`` directive. | |
+ | |
+.. _langext-__has_include: | |
+ | |
+``__has_include`` | |
+----------------- | |
+ | |
+This function-like macro takes a single file name string argument that is the | |
+name of an include file. It evaluates to 1 if the file can be found using the | |
+include paths, or 0 otherwise: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ // Note the two possible file name string formats. | |
+ #if __has_include("myinclude.h") && __has_include(<stdint.h>) | |
+ # include "myinclude.h" | |
+ #endif | |
+ | |
+ // To avoid problem with non-clang compilers not having this macro. | |
+ #if defined(__has_include) && __has_include("myinclude.h") | |
+ # include "myinclude.h" | |
+ #endif | |
+ | |
+To test for this feature, use ``#if defined(__has_include)``. | |
+ | |
+.. _langext-__has_include_next: | |
+ | |
+``__has_include_next`` | |
+---------------------- | |
+ | |
+This function-like macro takes a single file name string argument that is the | |
+name of an include file. It is like ``__has_include`` except that it looks for | |
+the second instance of the given file found in the include paths. It evaluates | |
+to 1 if the second instance of the file can be found using the include paths, | |
+or 0 otherwise: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ // Note the two possible file name string formats. | |
+ #if __has_include_next("myinclude.h") && __has_include_next(<stdint.h>) | |
+ # include_next "myinclude.h" | |
+ #endif | |
+ | |
+ // To avoid problem with non-clang compilers not having this macro. | |
+ #if defined(__has_include_next) && __has_include_next("myinclude.h") | |
+ # include_next "myinclude.h" | |
+ #endif | |
+ | |
+Note that ``__has_include_next``, like the GNU extension ``#include_next`` | |
+directive, is intended for use in headers only, and will issue a warning if | |
+used in the top-level compilation file. A warning will also be issued if an | |
+absolute path is used in the file argument. | |
+ | |
+``__has_warning`` | |
+----------------- | |
+ | |
+This function-like macro takes a string literal that represents a command line | |
+option for a warning and returns true if that is a valid warning option. | |
+ | |
+.. code-block:: c++ | |
+ | |
+ #if __has_warning("-Wformat") | |
+ ... | |
+ #endif | |
+ | |
+Builtin Macros | |
+============== | |
+ | |
+``__BASE_FILE__`` | |
+ Defined to a string that contains the name of the main input file passed to | |
+ Clang. | |
+ | |
+``__COUNTER__`` | |
+ Defined to an integer value that starts at zero and is incremented each time | |
+ the ``__COUNTER__`` macro is expanded. | |
+ | |
+``__INCLUDE_LEVEL__`` | |
+ Defined to an integral value that is the include depth of the file currently | |
+ being translated. For the main file, this value is zero. | |
+ | |
+``__TIMESTAMP__`` | |
+ Defined to the date and time of the last modification of the current source | |
+ file. | |
+ | |
+``__clang__`` | |
+ Defined when compiling with Clang | |
+ | |
+``__clang_major__`` | |
+ Defined to the major marketing version number of Clang (e.g., the 2 in | |
+ 2.0.1). Note that marketing version numbers should not be used to check for | |
+ language features, as different vendors use different numbering schemes. | |
+ Instead, use the :ref:`langext-feature_check`. | |
+ | |
+``__clang_minor__`` | |
+ Defined to the minor version number of Clang (e.g., the 0 in 2.0.1). Note | |
+ that marketing version numbers should not be used to check for language | |
+ features, as different vendors use different numbering schemes. Instead, use | |
+ the :ref:`langext-feature_check`. | |
+ | |
+``__clang_patchlevel__`` | |
+ Defined to the marketing patch level of Clang (e.g., the 1 in 2.0.1). | |
+ | |
+``__clang_version__`` | |
+ Defined to a string that captures the Clang marketing version, including the | |
+ Subversion tag or revision number, e.g., "``1.5 (trunk 102332)``". | |
+ | |
+.. _langext-vectors: | |
+ | |
+Vectors and Extended Vectors | |
+============================ | |
+ | |
+Supports the GCC, OpenCL, AltiVec and NEON vector extensions. | |
+ | |
+OpenCL vector types are created using ``ext_vector_type`` attribute. It | |
+support for ``V.xyzw`` syntax and other tidbits as seen in OpenCL. An example | |
+is: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ typedef float float4 __attribute__((ext_vector_type(4))); | |
+ typedef float float2 __attribute__((ext_vector_type(2))); | |
+ | |
+ float4 foo(float2 a, float2 b) { | |
+ float4 c; | |
+ c.xz = a; | |
+ c.yw = b; | |
+ return c; | |
+ } | |
+ | |
+Query for this feature with ``__has_extension(attribute_ext_vector_type)``. | |
+ | |
+Giving ``-faltivec`` option to clang enables support for AltiVec vector syntax | |
+and functions. For example: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ vector float foo(vector int a) { | |
+ vector int b; | |
+ b = vec_add(a, a) + a; | |
+ return (vector float)b; | |
+ } | |
+ | |
+NEON vector types are created using ``neon_vector_type`` and | |
+``neon_polyvector_type`` attributes. For example: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ typedef __attribute__((neon_vector_type(8))) int8_t int8x8_t; | |
+ typedef __attribute__((neon_polyvector_type(16))) poly8_t poly8x16_t; | |
+ | |
+ int8x8_t foo(int8x8_t a) { | |
+ int8x8_t v; | |
+ v = a; | |
+ return v; | |
+ } | |
+ | |
+Vector Literals | |
+--------------- | |
+ | |
+Vector literals can be used to create vectors from a set of scalars, or | |
+vectors. Either parentheses or braces form can be used. In the parentheses | |
+form the number of literal values specified must be one, i.e. referring to a | |
+scalar value, or must match the size of the vector type being created. If a | |
+single scalar literal value is specified, the scalar literal value will be | |
+replicated to all the components of the vector type. In the brackets form any | |
+number of literals can be specified. For example: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ typedef int v4si __attribute__((__vector_size__(16))); | |
+ typedef float float4 __attribute__((ext_vector_type(4))); | |
+ typedef float float2 __attribute__((ext_vector_type(2))); | |
+ | |
+ v4si vsi = (v4si){1, 2, 3, 4}; | |
+ float4 vf = (float4)(1.0f, 2.0f, 3.0f, 4.0f); | |
+ vector int vi1 = (vector int)(1); // vi1 will be (1, 1, 1, 1). | |
+ vector int vi2 = (vector int){1}; // vi2 will be (1, 0, 0, 0). | |
+ vector int vi3 = (vector int)(1, 2); // error | |
+ vector int vi4 = (vector int){1, 2}; // vi4 will be (1, 2, 0, 0). | |
+ vector int vi5 = (vector int)(1, 2, 3, 4); | |
+ float4 vf = (float4)((float2)(1.0f, 2.0f), (float2)(3.0f, 4.0f)); | |
+ | |
+Vector Operations | |
+----------------- | |
+ | |
+The table below shows the support for each operation by vector extension. A | |
+dash indicates that an operation is not accepted according to a corresponding | |
+specification. | |
+ | |
+============================== ====== ======= === ==== | |
+ Opeator OpenCL AltiVec GCC NEON | |
+============================== ====== ======= === ==== | |
+[] yes yes yes -- | |
+unary operators +, -- yes yes yes -- | |
+++, -- -- yes yes yes -- | |
++,--,*,/,% yes yes yes -- | |
+bitwise operators &,|,^,~ yes yes yes -- | |
+>>,<< yes yes yes -- | |
+!, &&, || no -- -- -- | |
+==, !=, >, <, >=, <= yes yes -- -- | |
+= yes yes yes yes | |
+:? yes -- -- -- | |
+sizeof yes yes yes yes | |
+============================== ====== ======= === ==== | |
+ | |
+See also :ref:`langext-__builtin_shufflevector`. | |
+ | |
+Messages on ``deprecated`` and ``unavailable`` Attributes | |
+========================================================= | |
+ | |
+An optional string message can be added to the ``deprecated`` and | |
+``unavailable`` attributes. For example: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!"))); | |
+ | |
+If the deprecated or unavailable declaration is used, the message will be | |
+incorporated into the appropriate diagnostic: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ harmless.c:4:3: warning: 'explode' is deprecated: extremely unsafe, use 'combust' instead!!! | |
+ [-Wdeprecated-declarations] | |
+ explode(); | |
+ ^ | |
+ | |
+Query for this feature with | |
+``__has_extension(attribute_deprecated_with_message)`` and | |
+``__has_extension(attribute_unavailable_with_message)``. | |
+ | |
+Attributes on Enumerators | |
+========================= | |
+ | |
+Clang allows attributes to be written on individual enumerators. This allows | |
+enumerators to be deprecated, made unavailable, etc. The attribute must appear | |
+after the enumerator name and before any initializer, like so: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ enum OperationMode { | |
+ OM_Invalid, | |
+ OM_Normal, | |
+ OM_Terrified __attribute__((deprecated)), | |
+ OM_AbortOnError __attribute__((deprecated)) = 4 | |
+ }; | |
+ | |
+Attributes on the ``enum`` declaration do not apply to individual enumerators. | |
+ | |
+Query for this feature with ``__has_extension(enumerator_attributes)``. | |
+ | |
+'User-Specified' System Frameworks | |
+================================== | |
+ | |
+Clang provides a mechanism by which frameworks can be built in such a way that | |
+they will always be treated as being "system frameworks", even if they are not | |
+present in a system framework directory. This can be useful to system | |
+framework developers who want to be able to test building other applications | |
+with development builds of their framework, including the manner in which the | |
+compiler changes warning behavior for system headers. | |
+ | |
+Framework developers can opt-in to this mechanism by creating a | |
+"``.system_framework``" file at the top-level of their framework. That is, the | |
+framework should have contents like: | |
+ | |
+.. code-block:: none | |
+ | |
+ .../TestFramework.framework | |
+ .../TestFramework.framework/.system_framework | |
+ .../TestFramework.framework/Headers | |
+ .../TestFramework.framework/Headers/TestFramework.h | |
+ ... | |
+ | |
+Clang will treat the presence of this file as an indicator that the framework | |
+should be treated as a system framework, regardless of how it was found in the | |
+framework search path. For consistency, we recommend that such files never be | |
+included in installed versions of the framework. | |
+ | |
+Availability attribute | |
+====================== | |
+ | |
+Clang introduces the ``availability`` attribute, which can be placed on | |
+declarations to describe the lifecycle of that declaration relative to | |
+operating system versions. Consider the function declaration for a | |
+hypothetical function ``f``: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ void f(void) __attribute__((availability(macosx,introduced=10.4,deprecated=10.6,obsoleted=10.7))); | |
+ | |
+The availability attribute states that ``f`` was introduced in Mac OS X 10.4, | |
+deprecated in Mac OS X 10.6, and obsoleted in Mac OS X 10.7. This information | |
+is used by Clang to determine when it is safe to use ``f``: for example, if | |
+Clang is instructed to compile code for Mac OS X 10.5, a call to ``f()`` | |
+succeeds. If Clang is instructed to compile code for Mac OS X 10.6, the call | |
+succeeds but Clang emits a warning specifying that the function is deprecated. | |
+Finally, if Clang is instructed to compile code for Mac OS X 10.7, the call | |
+fails because ``f()`` is no longer available. | |
+ | |
+The availablility attribute is a comma-separated list starting with the | |
+platform name and then including clauses specifying important milestones in the | |
+declaration's lifetime (in any order) along with additional information. Those | |
+clauses can be: | |
+ | |
+introduced=\ *version* | |
+ The first version in which this declaration was introduced. | |
+ | |
+deprecated=\ *version* | |
+ The first version in which this declaration was deprecated, meaning that | |
+ users should migrate away from this API. | |
+ | |
+obsoleted=\ *version* | |
+ The first version in which this declaration was obsoleted, meaning that it | |
+ was removed completely and can no longer be used. | |
+ | |
+unavailable | |
+ This declaration is never available on this platform. | |
+ | |
+message=\ *string-literal* | |
+ Additional message text that Clang will provide when emitting a warning or | |
+ error about use of a deprecated or obsoleted declaration. Useful to direct | |
+ users to replacement APIs. | |
+ | |
+Multiple availability attributes can be placed on a declaration, which may | |
+correspond to different platforms. Only the availability attribute with the | |
+platform corresponding to the target platform will be used; any others will be | |
+ignored. If no availability attribute specifies availability for the current | |
+target platform, the availability attributes are ignored. Supported platforms | |
+are: | |
+ | |
+``ios`` | |
+ Apple's iOS operating system. The minimum deployment target is specified by | |
+ the ``-mios-version-min=*version*`` or ``-miphoneos-version-min=*version*`` | |
+ command-line arguments. | |
+ | |
+``macosx`` | |
+ Apple's Mac OS X operating system. The minimum deployment target is | |
+ specified by the ``-mmacosx-version-min=*version*`` command-line argument. | |
+ | |
+A declaration can be used even when deploying back to a platform version prior | |
+to when the declaration was introduced. When this happens, the declaration is | |
+`weakly linked | |
+<https://developer.apple.com/library/mac/#documentation/MacOSX/Conceptual/BPFrameworks/Concepts/WeakLinking.html>`_, | |
+as if the ``weak_import`` attribute were added to the declaration. A | |
+weakly-linked declaration may or may not be present a run-time, and a program | |
+can determine whether the declaration is present by checking whether the | |
+address of that declaration is non-NULL. | |
+ | |
+Checks for Standard Language Features | |
+===================================== | |
+ | |
+The ``__has_feature`` macro can be used to query if certain standard language | |
+features are enabled. The ``__has_extension`` macro can be used to query if | |
+language features are available as an extension when compiling for a standard | |
+which does not provide them. The features which can be tested are listed here. | |
+ | |
+C++98 | |
+----- | |
+ | |
+The features listed below are part of the C++98 standard. These features are | |
+enabled by default when compiling C++ code. | |
+ | |
+C++ exceptions | |
+^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_exceptions)`` to determine if C++ exceptions have been | |
+enabled. For example, compiling code with ``-fno-exceptions`` disables C++ | |
+exceptions. | |
+ | |
+C++ RTTI | |
+^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_rtti)`` to determine if C++ RTTI has been enabled. For | |
+example, compiling code with ``-fno-rtti`` disables the use of RTTI. | |
+ | |
+C++11 | |
+----- | |
+ | |
+The features listed below are part of the C++11 standard. As a result, all | |
+these features are enabled with the ``-std=c++11`` or ``-std=gnu++11`` option | |
+when compiling C++ code. | |
+ | |
+C++11 SFINAE includes access control | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_access_control_sfinae)`` or | |
+``__has_extension(cxx_access_control_sfinae)`` to determine whether | |
+access-control errors (e.g., calling a private constructor) are considered to | |
+be template argument deduction errors (aka SFINAE errors), per `C++ DR1170 | |
+<http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1170>`_. | |
+ | |
+C++11 alias templates | |
+^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_alias_templates)`` or | |
+``__has_extension(cxx_alias_templates)`` to determine if support for C++11's | |
+alias declarations and alias templates is enabled. | |
+ | |
+C++11 alignment specifiers | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_alignas)`` or ``__has_extension(cxx_alignas)`` to | |
+determine if support for alignment specifiers using ``alignas`` is enabled. | |
+ | |
+C++11 attributes | |
+^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_attributes)`` or ``__has_extension(cxx_attributes)`` to | |
+determine if support for attribute parsing with C++11's square bracket notation | |
+is enabled. | |
+ | |
+C++11 generalized constant expressions | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_constexpr)`` to determine if support for generalized | |
+constant expressions (e.g., ``constexpr``) is enabled. | |
+ | |
+C++11 ``decltype()`` | |
+^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_decltype)`` or ``__has_extension(cxx_decltype)`` to | |
+determine if support for the ``decltype()`` specifier is enabled. C++11's | |
+``decltype`` does not require type-completeness of a function call expression. | |
+Use ``__has_feature(cxx_decltype_incomplete_return_types)`` or | |
+``__has_extension(cxx_decltype_incomplete_return_types)`` to determine if | |
+support for this feature is enabled. | |
+ | |
+C++11 default template arguments in function templates | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_default_function_template_args)`` or | |
+``__has_extension(cxx_default_function_template_args)`` to determine if support | |
+for default template arguments in function templates is enabled. | |
+ | |
+C++11 ``default``\ ed functions | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_defaulted_functions)`` or | |
+``__has_extension(cxx_defaulted_functions)`` to determine if support for | |
+defaulted function definitions (with ``= default``) is enabled. | |
+ | |
+C++11 delegating constructors | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_delegating_constructors)`` to determine if support for | |
+delegating constructors is enabled. | |
+ | |
+C++11 ``deleted`` functions | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_deleted_functions)`` or | |
+``__has_extension(cxx_deleted_functions)`` to determine if support for deleted | |
+function definitions (with ``= delete``) is enabled. | |
+ | |
+C++11 explicit conversion functions | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_explicit_conversions)`` to determine if support for | |
+``explicit`` conversion functions is enabled. | |
+ | |
+C++11 generalized initializers | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_generalized_initializers)`` to determine if support for | |
+generalized initializers (using braced lists and ``std::initializer_list``) is | |
+enabled. | |
+ | |
+C++11 implicit move constructors/assignment operators | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_implicit_moves)`` to determine if Clang will implicitly | |
+generate move constructors and move assignment operators where needed. | |
+ | |
+C++11 inheriting constructors | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_inheriting_constructors)`` to determine if support for | |
+inheriting constructors is enabled. Clang does not currently implement this | |
+feature. | |
+ | |
+C++11 inline namespaces | |
+^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_inline_namespaces)`` or | |
+``__has_extension(cxx_inline_namespaces)`` to determine if support for inline | |
+namespaces is enabled. | |
+ | |
+C++11 lambdas | |
+^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_lambdas)`` or ``__has_extension(cxx_lambdas)`` to | |
+determine if support for lambdas is enabled. | |
+ | |
+C++11 local and unnamed types as template arguments | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_local_type_template_args)`` or | |
+``__has_extension(cxx_local_type_template_args)`` to determine if support for | |
+local and unnamed types as template arguments is enabled. | |
+ | |
+C++11 noexcept | |
+^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_noexcept)`` or ``__has_extension(cxx_noexcept)`` to | |
+determine if support for noexcept exception specifications is enabled. | |
+ | |
+C++11 in-class non-static data member initialization | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_nonstatic_member_init)`` to determine whether in-class | |
+initialization of non-static data members is enabled. | |
+ | |
+C++11 ``nullptr`` | |
+^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_nullptr)`` or ``__has_extension(cxx_nullptr)`` to | |
+determine if support for ``nullptr`` is enabled. | |
+ | |
+C++11 ``override control`` | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_override_control)`` or | |
+``__has_extension(cxx_override_control)`` to determine if support for the | |
+override control keywords is enabled. | |
+ | |
+C++11 reference-qualified functions | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_reference_qualified_functions)`` or | |
+``__has_extension(cxx_reference_qualified_functions)`` to determine if support | |
+for reference-qualified functions (e.g., member functions with ``&`` or ``&&`` | |
+applied to ``*this``) is enabled. | |
+ | |
+C++11 range-based ``for`` loop | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_range_for)`` or ``__has_extension(cxx_range_for)`` to | |
+determine if support for the range-based for loop is enabled. | |
+ | |
+C++11 raw string literals | |
+^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_raw_string_literals)`` to determine if support for raw | |
+string literals (e.g., ``R"x(foo\bar)x"``) is enabled. | |
+ | |
+C++11 rvalue references | |
+^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_rvalue_references)`` or | |
+``__has_extension(cxx_rvalue_references)`` to determine if support for rvalue | |
+references is enabled. | |
+ | |
+C++11 ``static_assert()`` | |
+^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_static_assert)`` or | |
+``__has_extension(cxx_static_assert)`` to determine if support for compile-time | |
+assertions using ``static_assert`` is enabled. | |
+ | |
+C++11 type inference | |
+^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_auto_type)`` or ``__has_extension(cxx_auto_type)`` to | |
+determine C++11 type inference is supported using the ``auto`` specifier. If | |
+this is disabled, ``auto`` will instead be a storage class specifier, as in C | |
+or C++98. | |
+ | |
+C++11 strongly typed enumerations | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_strong_enums)`` or | |
+``__has_extension(cxx_strong_enums)`` to determine if support for strongly | |
+typed, scoped enumerations is enabled. | |
+ | |
+C++11 trailing return type | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_trailing_return)`` or | |
+``__has_extension(cxx_trailing_return)`` to determine if support for the | |
+alternate function declaration syntax with trailing return type is enabled. | |
+ | |
+C++11 Unicode string literals | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_unicode_literals)`` to determine if support for Unicode | |
+string literals is enabled. | |
+ | |
+C++11 unrestricted unions | |
+^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_unrestricted_unions)`` to determine if support for | |
+unrestricted unions is enabled. | |
+ | |
+C++11 user-defined literals | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_user_literals)`` to determine if support for | |
+user-defined literals is enabled. | |
+ | |
+C++11 variadic templates | |
+^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(cxx_variadic_templates)`` or | |
+``__has_extension(cxx_variadic_templates)`` to determine if support for | |
+variadic templates is enabled. | |
+ | |
+C11 | |
+--- | |
+ | |
+The features listed below are part of the C11 standard. As a result, all these | |
+features are enabled with the ``-std=c11`` or ``-std=gnu11`` option when | |
+compiling C code. Additionally, because these features are all | |
+backward-compatible, they are available as extensions in all language modes. | |
+ | |
+C11 alignment specifiers | |
+^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(c_alignas)`` or ``__has_extension(c_alignas)`` to determine | |
+if support for alignment specifiers using ``_Alignas`` is enabled. | |
+ | |
+C11 atomic operations | |
+^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(c_atomic)`` or ``__has_extension(c_atomic)`` to determine | |
+if support for atomic types using ``_Atomic`` is enabled. Clang also provides | |
+:ref:`a set of builtins <langext-__c11_atomic>` which can be used to implement | |
+the ``<stdatomic.h>`` operations on ``_Atomic`` types. | |
+ | |
+C11 generic selections | |
+^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(c_generic_selections)`` or | |
+``__has_extension(c_generic_selections)`` to determine if support for generic | |
+selections is enabled. | |
+ | |
+As an extension, the C11 generic selection expression is available in all | |
+languages supported by Clang. The syntax is the same as that given in the C11 | |
+standard. | |
+ | |
+In C, type compatibility is decided according to the rules given in the | |
+appropriate standard, but in C++, which lacks the type compatibility rules used | |
+in C, types are considered compatible only if they are equivalent. | |
+ | |
+C11 ``_Static_assert()`` | |
+^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Use ``__has_feature(c_static_assert)`` or ``__has_extension(c_static_assert)`` | |
+to determine if support for compile-time assertions using ``_Static_assert`` is | |
+enabled. | |
+ | |
+Checks for Type Traits | |
+====================== | |
+ | |
+Clang supports the `GNU C++ type traits | |
+<http://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html>`_ and a subset of the | |
+`Microsoft Visual C++ Type traits | |
+<http://msdn.microsoft.com/en-us/library/ms177194(v=VS.100).aspx>`_. For each | |
+supported type trait ``__X``, ``__has_extension(X)`` indicates the presence of | |
+the type trait. For example: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ #if __has_extension(is_convertible_to) | |
+ template<typename From, typename To> | |
+ struct is_convertible_to { | |
+ static const bool value = __is_convertible_to(From, To); | |
+ }; | |
+ #else | |
+ // Emulate type trait | |
+ #endif | |
+ | |
+The following type traits are supported by Clang: | |
+ | |
+* ``__has_nothrow_assign`` (GNU, Microsoft) | |
+* ``__has_nothrow_copy`` (GNU, Microsoft) | |
+* ``__has_nothrow_constructor`` (GNU, Microsoft) | |
+* ``__has_trivial_assign`` (GNU, Microsoft) | |
+* ``__has_trivial_copy`` (GNU, Microsoft) | |
+* ``__has_trivial_constructor`` (GNU, Microsoft) | |
+* ``__has_trivial_destructor`` (GNU, Microsoft) | |
+* ``__has_virtual_destructor`` (GNU, Microsoft) | |
+* ``__is_abstract`` (GNU, Microsoft) | |
+* ``__is_base_of`` (GNU, Microsoft) | |
+* ``__is_class`` (GNU, Microsoft) | |
+* ``__is_convertible_to`` (Microsoft) | |
+* ``__is_empty`` (GNU, Microsoft) | |
+* ``__is_enum`` (GNU, Microsoft) | |
+* ``__is_interface_class`` (Microsoft) | |
+* ``__is_pod`` (GNU, Microsoft) | |
+* ``__is_polymorphic`` (GNU, Microsoft) | |
+* ``__is_union`` (GNU, Microsoft) | |
+* ``__is_literal(type)``: Determines whether the given type is a literal type | |
+* ``__is_final``: Determines whether the given type is declared with a | |
+ ``final`` class-virt-specifier. | |
+* ``__underlying_type(type)``: Retrieves the underlying type for a given | |
+ ``enum`` type. This trait is required to implement the C++11 standard | |
+ library. | |
+* ``__is_trivially_assignable(totype, fromtype)``: Determines whether a value | |
+ of type ``totype`` can be assigned to from a value of type ``fromtype`` such | |
+ that no non-trivial functions are called as part of that assignment. This | |
+ trait is required to implement the C++11 standard library. | |
+* ``__is_trivially_constructible(type, argtypes...)``: Determines whether a | |
+ value of type ``type`` can be direct-initialized with arguments of types | |
+ ``argtypes...`` such that no non-trivial functions are called as part of | |
+ that initialization. This trait is required to implement the C++11 standard | |
+ library. | |
+ | |
+Blocks | |
+====== | |
+ | |
+The syntax and high level language feature description is in | |
+`BlockLanguageSpec.txt <BlockLanguageSpec.txt>`_. Implementation and ABI | |
+details for the clang implementation are in `Block-ABI-Apple.txt | |
+<Block-ABI-Apple.txt>`_. | |
+ | |
+Query for this feature with ``__has_extension(blocks)``. | |
+ | |
+Objective-C Features | |
+==================== | |
+ | |
+Related result types | |
+-------------------- | |
+ | |
+According to Cocoa conventions, Objective-C methods with certain names | |
+("``init``", "``alloc``", etc.) always return objects that are an instance of | |
+the receiving class's type. Such methods are said to have a "related result | |
+type", meaning that a message send to one of these methods will have the same | |
+static type as an instance of the receiver class. For example, given the | |
+following classes: | |
+ | |
+.. code-block:: objc | |
+ | |
+ @interface NSObject | |
+ + (id)alloc; | |
+ - (id)init; | |
+ @end | |
+ | |
+ @interface NSArray : NSObject | |
+ @end | |
+ | |
+and this common initialization pattern | |
+ | |
+.. code-block:: objc | |
+ | |
+ NSArray *array = [[NSArray alloc] init]; | |
+ | |
+the type of the expression ``[NSArray alloc]`` is ``NSArray*`` because | |
+``alloc`` implicitly has a related result type. Similarly, the type of the | |
+expression ``[[NSArray alloc] init]`` is ``NSArray*``, since ``init`` has a | |
+related result type and its receiver is known to have the type ``NSArray *``. | |
+If neither ``alloc`` nor ``init`` had a related result type, the expressions | |
+would have had type ``id``, as declared in the method signature. | |
+ | |
+A method with a related result type can be declared by using the type | |
+``instancetype`` as its result type. ``instancetype`` is a contextual keyword | |
+that is only permitted in the result type of an Objective-C method, e.g. | |
+ | |
+.. code-block:: objc | |
+ | |
+ @interface A | |
+ + (instancetype)constructAnA; | |
+ @end | |
+ | |
+The related result type can also be inferred for some methods. To determine | |
+whether a method has an inferred related result type, the first word in the | |
+camel-case selector (e.g., "``init``" in "``initWithObjects``") is considered, | |
+and the method will have a related result type if its return type is compatible | |
+with the type of its class and if: | |
+ | |
+* the first word is "``alloc``" or "``new``", and the method is a class method, | |
+ or | |
+ | |
+* the first word is "``autorelease``", "``init``", "``retain``", or "``self``", | |
+ and the method is an instance method. | |
+ | |
+If a method with a related result type is overridden by a subclass method, the | |
+subclass method must also return a type that is compatible with the subclass | |
+type. For example: | |
+ | |
+.. code-block:: objc | |
+ | |
+ @interface NSString : NSObject | |
+ - (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString | |
+ @end | |
+ | |
+Related result types only affect the type of a message send or property access | |
+via the given method. In all other respects, a method with a related result | |
+type is treated the same way as method that returns ``id``. | |
+ | |
+Use ``__has_feature(objc_instancetype)`` to determine whether the | |
+``instancetype`` contextual keyword is available. | |
+ | |
+Automatic reference counting | |
+---------------------------- | |
+ | |
+Clang provides support for `automated reference counting | |
+<AutomaticReferenceCounting.html>`_ in Objective-C, which eliminates the need | |
+for manual ``retain``/``release``/``autorelease`` message sends. There are two | |
+feature macros associated with automatic reference counting: | |
+``__has_feature(objc_arc)`` indicates the availability of automated reference | |
+counting in general, while ``__has_feature(objc_arc_weak)`` indicates that | |
+automated reference counting also includes support for ``__weak`` pointers to | |
+Objective-C objects. | |
+ | |
+Enumerations with a fixed underlying type | |
+----------------------------------------- | |
+ | |
+Clang provides support for C++11 enumerations with a fixed underlying type | |
+within Objective-C. For example, one can write an enumeration type as: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ typedef enum : unsigned char { Red, Green, Blue } Color; | |
+ | |
+This specifies that the underlying type, which is used to store the enumeration | |
+value, is ``unsigned char``. | |
+ | |
+Use ``__has_feature(objc_fixed_enum)`` to determine whether support for fixed | |
+underlying types is available in Objective-C. | |
+ | |
+Interoperability with C++11 lambdas | |
+----------------------------------- | |
+ | |
+Clang provides interoperability between C++11 lambdas and blocks-based APIs, by | |
+permitting a lambda to be implicitly converted to a block pointer with the | |
+corresponding signature. For example, consider an API such as ``NSArray``'s | |
+array-sorting method: | |
+ | |
+.. code-block:: objc | |
+ | |
+ - (NSArray *)sortedArrayUsingComparator:(NSComparator)cmptr; | |
+ | |
+``NSComparator`` is simply a typedef for the block pointer ``NSComparisonResult | |
+(^)(id, id)``, and parameters of this type are generally provided with block | |
+literals as arguments. However, one can also use a C++11 lambda so long as it | |
+provides the same signature (in this case, accepting two parameters of type | |
+``id`` and returning an ``NSComparisonResult``): | |
+ | |
+.. code-block:: objc | |
+ | |
+ NSArray *array = @[@"string 1", @"string 21", @"string 12", @"String 11", | |
+ @"String 02"]; | |
+ const NSStringCompareOptions comparisonOptions | |
+ = NSCaseInsensitiveSearch | NSNumericSearch | | |
+ NSWidthInsensitiveSearch | NSForcedOrderingSearch; | |
+ NSLocale *currentLocale = [NSLocale currentLocale]; | |
+ NSArray *sorted | |
+ = [array sortedArrayUsingComparator:[=](id s1, id s2) -> NSComparisonResult { | |
+ NSRange string1Range = NSMakeRange(0, [s1 length]); | |
+ return [s1 compare:s2 options:comparisonOptions | |
+ range:string1Range locale:currentLocale]; | |
+ }]; | |
+ NSLog(@"sorted: %@", sorted); | |
+ | |
+This code relies on an implicit conversion from the type of the lambda | |
+expression (an unnamed, local class type called the *closure type*) to the | |
+corresponding block pointer type. The conversion itself is expressed by a | |
+conversion operator in that closure type that produces a block pointer with the | |
+same signature as the lambda itself, e.g., | |
+ | |
+.. code-block:: objc | |
+ | |
+ operator NSComparisonResult (^)(id, id)() const; | |
+ | |
+This conversion function returns a new block that simply forwards the two | |
+parameters to the lambda object (which it captures by copy), then returns the | |
+result. The returned block is first copied (with ``Block_copy``) and then | |
+autoreleased. As an optimization, if a lambda expression is immediately | |
+converted to a block pointer (as in the first example, above), then the block | |
+is not copied and autoreleased: rather, it is given the same lifetime as a | |
+block literal written at that point in the program, which avoids the overhead | |
+of copying a block to the heap in the common case. | |
+ | |
+The conversion from a lambda to a block pointer is only available in | |
+Objective-C++, and not in C++ with blocks, due to its use of Objective-C memory | |
+management (autorelease). | |
+ | |
+Object Literals and Subscripting | |
+-------------------------------- | |
+ | |
+Clang provides support for `Object Literals and Subscripting | |
+<ObjectiveCLiterals.html>`_ in Objective-C, which simplifies common Objective-C | |
+programming patterns, makes programs more concise, and improves the safety of | |
+container creation. There are several feature macros associated with object | |
+literals and subscripting: ``__has_feature(objc_array_literals)`` tests the | |
+availability of array literals; ``__has_feature(objc_dictionary_literals)`` | |
+tests the availability of dictionary literals; | |
+``__has_feature(objc_subscripting)`` tests the availability of object | |
+subscripting. | |
+ | |
+Objective-C Autosynthesis of Properties | |
+--------------------------------------- | |
+ | |
+Clang provides support for autosynthesis of declared properties. Using this | |
+feature, clang provides default synthesis of those properties not declared | |
+@dynamic and not having user provided backing getter and setter methods. | |
+``__has_feature(objc_default_synthesize_properties)`` checks for availability | |
+of this feature in version of clang being used. | |
+ | |
+Function Overloading in C | |
+========================= | |
+ | |
+Clang provides support for C++ function overloading in C. Function overloading | |
+in C is introduced using the ``overloadable`` attribute. For example, one | |
+might provide several overloaded versions of a ``tgsin`` function that invokes | |
+the appropriate standard function computing the sine of a value with ``float``, | |
+``double``, or ``long double`` precision: | |
+ | |
+.. code-block:: c | |
+ | |
+ #include <math.h> | |
+ float __attribute__((overloadable)) tgsin(float x) { return sinf(x); } | |
+ double __attribute__((overloadable)) tgsin(double x) { return sin(x); } | |
+ long double __attribute__((overloadable)) tgsin(long double x) { return sinl(x); } | |
+ | |
+Given these declarations, one can call ``tgsin`` with a ``float`` value to | |
+receive a ``float`` result, with a ``double`` to receive a ``double`` result, | |
+etc. Function overloading in C follows the rules of C++ function overloading | |
+to pick the best overload given the call arguments, with a few C-specific | |
+semantics: | |
+ | |
+* Conversion from ``float`` or ``double`` to ``long double`` is ranked as a | |
+ floating-point promotion (per C99) rather than as a floating-point conversion | |
+ (as in C++). | |
+ | |
+* A conversion from a pointer of type ``T*`` to a pointer of type ``U*`` is | |
+ considered a pointer conversion (with conversion rank) if ``T`` and ``U`` are | |
+ compatible types. | |
+ | |
+* A conversion from type ``T`` to a value of type ``U`` is permitted if ``T`` | |
+ and ``U`` are compatible types. This conversion is given "conversion" rank. | |
+ | |
+The declaration of ``overloadable`` functions is restricted to function | |
+declarations and definitions. Most importantly, if any function with a given | |
+name is given the ``overloadable`` attribute, then all function declarations | |
+and definitions with that name (and in that scope) must have the | |
+``overloadable`` attribute. This rule even applies to redeclarations of | |
+functions whose original declaration had the ``overloadable`` attribute, e.g., | |
+ | |
+.. code-block:: c | |
+ | |
+ int f(int) __attribute__((overloadable)); | |
+ float f(float); // error: declaration of "f" must have the "overloadable" attribute | |
+ | |
+ int g(int) __attribute__((overloadable)); | |
+ int g(int) { } // error: redeclaration of "g" must also have the "overloadable" attribute | |
+ | |
+Functions marked ``overloadable`` must have prototypes. Therefore, the | |
+following code is ill-formed: | |
+ | |
+.. code-block:: c | |
+ | |
+ int h() __attribute__((overloadable)); // error: h does not have a prototype | |
+ | |
+However, ``overloadable`` functions are allowed to use a ellipsis even if there | |
+are no named parameters (as is permitted in C++). This feature is particularly | |
+useful when combined with the ``unavailable`` attribute: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ void honeypot(...) __attribute__((overloadable, unavailable)); // calling me is an error | |
+ | |
+Functions declared with the ``overloadable`` attribute have their names mangled | |
+according to the same rules as C++ function names. For example, the three | |
+``tgsin`` functions in our motivating example get the mangled names | |
+``_Z5tgsinf``, ``_Z5tgsind``, and ``_Z5tgsine``, respectively. There are two | |
+caveats to this use of name mangling: | |
+ | |
+* Future versions of Clang may change the name mangling of functions overloaded | |
+ in C, so you should not depend on an specific mangling. To be completely | |
+ safe, we strongly urge the use of ``static inline`` with ``overloadable`` | |
+ functions. | |
+ | |
+* The ``overloadable`` attribute has almost no meaning when used in C++, | |
+ because names will already be mangled and functions are already overloadable. | |
+ However, when an ``overloadable`` function occurs within an ``extern "C"`` | |
+ linkage specification, it's name *will* be mangled in the same way as it | |
+ would in C. | |
+ | |
+Query for this feature with ``__has_extension(attribute_overloadable)``. | |
+ | |
+Initializer lists for complex numbers in C | |
+========================================== | |
+ | |
+clang supports an extension which allows the following in C: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ #include <math.h> | |
+ #include <complex.h> | |
+ complex float x = { 1.0f, INFINITY }; // Init to (1, Inf) | |
+ | |
+This construct is useful because there is no way to separately initialize the | |
+real and imaginary parts of a complex variable in standard C, given that clang | |
+does not support ``_Imaginary``. (Clang also supports the ``__real__`` and | |
+``__imag__`` extensions from gcc, which help in some cases, but are not usable | |
+in static initializers.) | |
+ | |
+Note that this extension does not allow eliding the braces; the meaning of the | |
+following two lines is different: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1) | |
+ complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0) | |
+ | |
+This extension also works in C++ mode, as far as that goes, but does not apply | |
+to the C++ ``std::complex``. (In C++11, list initialization allows the same | |
+syntax to be used with ``std::complex`` with the same meaning.) | |
+ | |
+Builtin Functions | |
+================= | |
+ | |
+Clang supports a number of builtin library functions with the same syntax as | |
+GCC, including things like ``__builtin_nan``, ``__builtin_constant_p``, | |
+``__builtin_choose_expr``, ``__builtin_types_compatible_p``, | |
+``__sync_fetch_and_add``, etc. In addition to the GCC builtins, Clang supports | |
+a number of builtins that GCC does not, which are listed here. | |
+ | |
+Please note that Clang does not and will not support all of the GCC builtins | |
+for vector operations. Instead of using builtins, you should use the functions | |
+defined in target-specific header files like ``<xmmintrin.h>``, which define | |
+portable wrappers for these. Many of the Clang versions of these functions are | |
+implemented directly in terms of :ref:`extended vector support | |
+<langext-vectors>` instead of builtins, in order to reduce the number of | |
+builtins that we need to implement. | |
+ | |
+``__builtin_readcyclecounter`` | |
+------------------------------ | |
+ | |
+``__builtin_readcyclecounter`` is used to access the cycle counter register (or | |
+a similar low-latency, high-accuracy clock) on those targets that support it. | |
+ | |
+**Syntax**: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ __builtin_readcyclecounter() | |
+ | |
+**Example of Use**: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ unsigned long long t0 = __builtin_readcyclecounter(); | |
+ do_something(); | |
+ unsigned long long t1 = __builtin_readcyclecounter(); | |
+ unsigned long long cycles_to_do_something = t1 - t0; // assuming no overflow | |
+ | |
+**Description**: | |
+ | |
+The ``__builtin_readcyclecounter()`` builtin returns the cycle counter value, | |
+which may be either global or process/thread-specific depending on the target. | |
+As the backing counters often overflow quickly (on the order of seconds) this | |
+should only be used for timing small intervals. When not supported by the | |
+target, the return value is always zero. This builtin takes no arguments and | |
+produces an unsigned long long result. | |
+ | |
+Query for this feature with ``__has_builtin(__builtin_readcyclecounter)``. | |
+ | |
+.. _langext-__builtin_shufflevector: | |
+ | |
+``__builtin_shufflevector`` | |
+--------------------------- | |
+ | |
+``__builtin_shufflevector`` is used to express generic vector | |
+permutation/shuffle/swizzle operations. This builtin is also very important | |
+for the implementation of various target-specific header files like | |
+``<xmmintrin.h>``. | |
+ | |
+**Syntax**: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ __builtin_shufflevector(vec1, vec2, index1, index2, ...) | |
+ | |
+**Examples**: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ // Identity operation - return 4-element vector V1. | |
+ __builtin_shufflevector(V1, V1, 0, 1, 2, 3) | |
+ | |
+ // "Splat" element 0 of V1 into a 4-element result. | |
+ __builtin_shufflevector(V1, V1, 0, 0, 0, 0) | |
+ | |
+ // Reverse 4-element vector V1. | |
+ __builtin_shufflevector(V1, V1, 3, 2, 1, 0) | |
+ | |
+ // Concatenate every other element of 4-element vectors V1 and V2. | |
+ __builtin_shufflevector(V1, V2, 0, 2, 4, 6) | |
+ | |
+ // Concatenate every other element of 8-element vectors V1 and V2. | |
+ __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14) | |
+ | |
+**Description**: | |
+ | |
+The first two arguments to ``__builtin_shufflevector`` are vectors that have | |
+the same element type. The remaining arguments are a list of integers that | |
+specify the elements indices of the first two vectors that should be extracted | |
+and returned in a new vector. These element indices are numbered sequentially | |
+starting with the first vector, continuing into the second vector. Thus, if | |
+``vec1`` is a 4-element vector, index 5 would refer to the second element of | |
+``vec2``. | |
+ | |
+The result of ``__builtin_shufflevector`` is a vector with the same element | |
+type as ``vec1``/``vec2`` but that has an element count equal to the number of | |
+indices specified. | |
+ | |
+Query for this feature with ``__has_builtin(__builtin_shufflevector)``. | |
+ | |
+``__builtin_unreachable`` | |
+------------------------- | |
+ | |
+``__builtin_unreachable`` is used to indicate that a specific point in the | |
+program cannot be reached, even if the compiler might otherwise think it can. | |
+This is useful to improve optimization and eliminates certain warnings. For | |
+example, without the ``__builtin_unreachable`` in the example below, the | |
+compiler assumes that the inline asm can fall through and prints a "function | |
+declared '``noreturn``' should not return" warning. | |
+ | |
+**Syntax**: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ __builtin_unreachable() | |
+ | |
+**Example of use**: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ void myabort(void) __attribute__((noreturn)); | |
+ void myabort(void) { | |
+ asm("int3"); | |
+ __builtin_unreachable(); | |
+ } | |
+ | |
+**Description**: | |
+ | |
+The ``__builtin_unreachable()`` builtin has completely undefined behavior. | |
+Since it has undefined behavior, it is a statement that it is never reached and | |
+the optimizer can take advantage of this to produce better code. This builtin | |
+takes no arguments and produces a void result. | |
+ | |
+Query for this feature with ``__has_builtin(__builtin_unreachable)``. | |
+ | |
+``__sync_swap`` | |
+--------------- | |
+ | |
+``__sync_swap`` is used to atomically swap integers or pointers in memory. | |
+ | |
+**Syntax**: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ type __sync_swap(type *ptr, type value, ...) | |
+ | |
+**Example of Use**: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ int old_value = __sync_swap(&value, new_value); | |
+ | |
+**Description**: | |
+ | |
+The ``__sync_swap()`` builtin extends the existing ``__sync_*()`` family of | |
+atomic intrinsics to allow code to atomically swap the current value with the | |
+new value. More importantly, it helps developers write more efficient and | |
+correct code by avoiding expensive loops around | |
+``__sync_bool_compare_and_swap()`` or relying on the platform specific | |
+implementation details of ``__sync_lock_test_and_set()``. The | |
+``__sync_swap()`` builtin is a full barrier. | |
+ | |
+.. _langext-__c11_atomic: | |
+ | |
+__c11_atomic builtins | |
+--------------------- | |
+ | |
+Clang provides a set of builtins which are intended to be used to implement | |
+C11's ``<stdatomic.h>`` header. These builtins provide the semantics of the | |
+``_explicit`` form of the corresponding C11 operation, and are named with a | |
+``__c11_`` prefix. The supported operations are: | |
+ | |
+* ``__c11_atomic_init`` | |
+* ``__c11_atomic_thread_fence`` | |
+* ``__c11_atomic_signal_fence`` | |
+* ``__c11_atomic_is_lock_free`` | |
+* ``__c11_atomic_store`` | |
+* ``__c11_atomic_load`` | |
+* ``__c11_atomic_exchange`` | |
+* ``__c11_atomic_compare_exchange_strong`` | |
+* ``__c11_atomic_compare_exchange_weak`` | |
+* ``__c11_atomic_fetch_add`` | |
+* ``__c11_atomic_fetch_sub`` | |
+* ``__c11_atomic_fetch_and`` | |
+* ``__c11_atomic_fetch_or`` | |
+* ``__c11_atomic_fetch_xor`` | |
+ | |
+Non-standard C++11 Attributes | |
+============================= | |
+ | |
+Clang supports one non-standard C++11 attribute. It resides in the ``clang`` | |
+attribute namespace. | |
+ | |
+The ``clang::fallthrough`` attribute | |
+------------------------------------ | |
+ | |
+The ``clang::fallthrough`` attribute is used along with the | |
+``-Wimplicit-fallthrough`` argument to annotate intentional fall-through | |
+between switch labels. It can only be applied to a null statement placed at a | |
+point of execution between any statement and the next switch label. It is | |
+common to mark these places with a specific comment, but this attribute is | |
+meant to replace comments with a more strict annotation, which can be checked | |
+by the compiler. This attribute doesn't change semantics of the code and can | |
+be used wherever an intended fall-through occurs. It is designed to mimic | |
+control-flow statements like ``break;``, so it can be placed in most places | |
+where ``break;`` can, but only if there are no statements on the execution path | |
+between it and the next switch label. | |
+ | |
+Here is an example: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ // compile with -Wimplicit-fallthrough | |
+ switch (n) { | |
+ case 22: | |
+ case 33: // no warning: no statements between case labels | |
+ f(); | |
+ case 44: // warning: unannotated fall-through | |
+ g(); | |
+ [[clang::fallthrough]]; | |
+ case 55: // no warning | |
+ if (x) { | |
+ h(); | |
+ break; | |
+ } | |
+ else { | |
+ i(); | |
+ [[clang::fallthrough]]; | |
+ } | |
+ case 66: // no warning | |
+ p(); | |
+ [[clang::fallthrough]]; // warning: fallthrough annotation does not | |
+ // directly precede case label | |
+ q(); | |
+ case 77: // warning: unannotated fall-through | |
+ r(); | |
+ } | |
+ | |
+Target-Specific Extensions | |
+========================== | |
+ | |
+Clang supports some language features conditionally on some targets. | |
+ | |
+X86/X86-64 Language Extensions | |
+------------------------------ | |
+ | |
+The X86 backend has these language extensions: | |
+ | |
+Memory references off the GS segment | |
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
+ | |
+Annotating a pointer with address space #256 causes it to be code generated | |
+relative to the X86 GS segment register, and address space #257 causes it to be | |
+relative to the X86 FS segment. Note that this is a very very low-level | |
+feature that should only be used if you know what you're doing (for example in | |
+an OS kernel). | |
+ | |
+Here is an example: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ #define GS_RELATIVE __attribute__((address_space(256))) | |
+ int foo(int GS_RELATIVE *P) { | |
+ return *P; | |
+ } | |
+ | |
+Which compiles to (on X86-32): | |
+ | |
+.. code-block:: gas | |
+ | |
+ _foo: | |
+ movl 4(%esp), %eax | |
+ movl %gs:(%eax), %eax | |
+ ret | |
+ | |
+Static Analysis-Specific Extensions | |
+=================================== | |
+ | |
+Clang supports additional attributes that are useful for documenting program | |
+invariants and rules for static analysis tools. The extensions documented here | |
+are used by the `path-sensitive static analyzer engine | |
+<http://clang.llvm.org/StaticAnalysis.html>`_ that is part of Clang's Analysis | |
+library. | |
+ | |
+The ``analyzer_noreturn`` attribute | |
+----------------------------------- | |
+ | |
+Clang's static analysis engine understands the standard ``noreturn`` attribute. | |
+This attribute, which is typically affixed to a function prototype, indicates | |
+that a call to a given function never returns. Function prototypes for common | |
+functions like ``exit`` are typically annotated with this attribute, as well as | |
+a variety of common assertion handlers. Users can educate the static analyzer | |
+about their own custom assertion handles (thus cutting down on false positives | |
+due to false paths) by marking their own "panic" functions with this attribute. | |
+ | |
+While useful, ``noreturn`` is not applicable in all cases. Sometimes there are | |
+special functions that for all intents and purposes should be considered panic | |
+functions (i.e., they are only called when an internal program error occurs) | |
+but may actually return so that the program can fail gracefully. The | |
+``analyzer_noreturn`` attribute allows one to annotate such functions as being | |
+interpreted as "no return" functions by the analyzer (thus pruning bogus paths) | |
+but will not affect compilation (as in the case of ``noreturn``). | |
+ | |
+**Usage**: The ``analyzer_noreturn`` attribute can be placed in the same places | |
+where the ``noreturn`` attribute can be placed. It is commonly placed at the | |
+end of function prototypes: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ void foo() __attribute__((analyzer_noreturn)); | |
+ | |
+Query for this feature with ``__has_attribute(analyzer_noreturn)``. | |
+ | |
+.. _langext-objc_method_family: | |
+ | |
+The ``objc_method_family`` attribute | |
+------------------------------------ | |
+ | |
+Many methods in Objective-C have conventional meanings determined by their | |
+selectors. For the purposes of static analysis, it is sometimes useful to be | |
+able to mark a method as having a particular conventional meaning despite not | |
+having the right selector, or as not having the conventional meaning that its | |
+selector would suggest. For these use cases, we provide an attribute to | |
+specifically describe the "method family" that a method belongs to. | |
+ | |
+**Usage**: ``__attribute__((objc_method_family(X)))``, where ``X`` is one of | |
+``none``, ``alloc``, ``copy``, ``init``, ``mutableCopy``, or ``new``. This | |
+attribute can only be placed at the end of a method declaration: | |
+ | |
+.. code-block:: objc | |
+ | |
+ - (NSString*) initMyStringValue __attribute__((objc_method_family(none))); | |
+ | |
+Users who do not wish to change the conventional meaning of a method, and who | |
+merely want to document its non-standard retain and release semantics, should | |
+use the :ref:`retaining behavior attributes <langext-objc-retain-release>` | |
+described below. | |
+ | |
+Query for this feature with ``__has_attribute(objc_method_family)``. | |
+ | |
+.. _langext-objc-retain-release: | |
+ | |
+Objective-C retaining behavior attributes | |
+----------------------------------------- | |
+ | |
+In Objective-C, functions and methods are generally assumed to take and return | |
+objects with +0 retain counts, with some exceptions for special methods like | |
+``+alloc`` and ``init``. However, there are exceptions, and so Clang provides | |
+attributes to allow these exceptions to be documented, which helps the analyzer | |
+find leaks (and ignore non-leaks). Some exceptions may be better described | |
+using the :ref:`objc_method_family <langext-objc_method_family>` attribute | |
+instead. | |
+ | |
+**Usage**: The ``ns_returns_retained``, ``ns_returns_not_retained``, | |
+ ``ns_returns_autoreleased``, ``cf_returns_retained``, and | |
+ ``cf_returns_not_retained`` attributes can be placed on methods and functions | |
+ that return Objective-C or CoreFoundation objects. They are commonly placed | |
+ at the end of a function prototype or method declaration: | |
+ | |
+.. code-block:: objc | |
+ | |
+ id foo() __attribute__((ns_returns_retained)); | |
+ | |
+ - (NSString*) bar: (int) x __attribute__((ns_returns_retained)); | |
+ | |
+The ``*_returns_retained`` attributes specify that the returned object has a +1 | |
+retain count. The ``*_returns_not_retained`` attributes specify that the return | |
+object has a +0 retain count, even if the normal convention for its selector | |
+would be +1. ``ns_returns_autoreleased`` specifies that the returned object is | |
++0, but is guaranteed to live at least as long as the next flush of an | |
+autorelease pool. | |
+ | |
+**Usage**: The ``ns_consumed`` and ``cf_consumed`` attributes can be placed on | |
+an parameter declaration; they specify that the argument is expected to have a | |
++1 retain count, which will be balanced in some way by the function or method. | |
+The ``ns_consumes_self`` attribute can only be placed on an Objective-C | |
+method; it specifies that the method expects its ``self`` parameter to have a | |
++1 retain count, which it will balance in some way. | |
+ | |
+.. code-block:: objc | |
+ | |
+ void foo(__attribute__((ns_consumed)) NSString *string); | |
+ | |
+ - (void) bar __attribute__((ns_consumes_self)); | |
+ - (void) baz: (id) __attribute__((ns_consumed)) x; | |
+ | |
+Query for these features with ``__has_attribute(ns_consumed)``, | |
+``__has_attribute(ns_returns_retained)``, etc. | |
+ | |
+Dynamic Analysis-Specific Extensions | |
+==================================== | |
+ | |
+.. _langext-address_sanitizer: | |
+ | |
+AddressSanitizer | |
+---------------- | |
+ | |
+Use ``__has_feature(address_sanitizer)`` to check if the code is being built | |
+with `AddressSanitizer <AddressSanitizer.html>`_. | |
+ | |
+Use ``__attribute__((no_address_safety_analysis))`` on a function declaration | |
+to specify that address safety instrumentation (e.g. AddressSanitizer) should | |
+not be applied to that function. | |
+ | |
+Thread-Safety Annotation Checking | |
+================================= | |
+ | |
+Clang supports additional attributes for checking basic locking policies in | |
+multithreaded programs. Clang currently parses the following list of | |
+attributes, although **the implementation for these annotations is currently in | |
+development.** For more details, see the `GCC implementation | |
+<http://gcc.gnu.org/wiki/ThreadSafetyAnnotation>`_. | |
+ | |
+``no_thread_safety_analysis`` | |
+----------------------------- | |
+ | |
+Use ``__attribute__((no_thread_safety_analysis))`` on a function declaration to | |
+specify that the thread safety analysis should not be run on that function. | |
+This attribute provides an escape hatch (e.g. for situations when it is | |
+difficult to annotate the locking policy). | |
+ | |
+``lockable`` | |
+------------ | |
+ | |
+Use ``__attribute__((lockable))`` on a class definition to specify that it has | |
+a lockable type (e.g. a Mutex class). This annotation is primarily used to | |
+check consistency. | |
+ | |
+``scoped_lockable`` | |
+------------------- | |
+ | |
+Use ``__attribute__((scoped_lockable))`` on a class definition to specify that | |
+it has a "scoped" lockable type. Objects of this type will acquire the lock | |
+upon construction and release it upon going out of scope. This annotation is | |
+primarily used to check consistency. | |
+ | |
+``guarded_var`` | |
+--------------- | |
+ | |
+Use ``__attribute__((guarded_var))`` on a variable declaration to specify that | |
+the variable must be accessed while holding some lock. | |
+ | |
+``pt_guarded_var`` | |
+------------------ | |
+ | |
+Use ``__attribute__((pt_guarded_var))`` on a pointer declaration to specify | |
+that the pointer must be dereferenced while holding some lock. | |
+ | |
+``guarded_by(l)`` | |
+----------------- | |
+ | |
+Use ``__attribute__((guarded_by(l)))`` on a variable declaration to specify | |
+that the variable must be accessed while holding lock ``l``. | |
+ | |
+``pt_guarded_by(l)`` | |
+-------------------- | |
+ | |
+Use ``__attribute__((pt_guarded_by(l)))`` on a pointer declaration to specify | |
+that the pointer must be dereferenced while holding lock ``l``. | |
+ | |
+``acquired_before(...)`` | |
+------------------------ | |
+ | |
+Use ``__attribute__((acquired_before(...)))`` on a declaration of a lockable | |
+variable to specify that the lock must be acquired before all attribute | |
+arguments. Arguments must be lockable type, and there must be at least one | |
+argument. | |
+ | |
+``acquired_after(...)`` | |
+----------------------- | |
+ | |
+Use ``__attribute__((acquired_after(...)))`` on a declaration of a lockable | |
+variable to specify that the lock must be acquired after all attribute | |
+arguments. Arguments must be lockable type, and there must be at least one | |
+argument. | |
+ | |
+``exclusive_lock_function(...)`` | |
+-------------------------------- | |
+ | |
+Use ``__attribute__((exclusive_lock_function(...)))`` on a function declaration | |
+to specify that the function acquires all listed locks exclusively. This | |
+attribute takes zero or more arguments: either of lockable type or integers | |
+indexing into function parameters of lockable type. If no arguments are given, | |
+the acquired lock is implicitly ``this`` of the enclosing object. | |
+ | |
+``shared_lock_function(...)`` | |
+----------------------------- | |
+ | |
+Use ``__attribute__((shared_lock_function(...)))`` on a function declaration to | |
+specify that the function acquires all listed locks, although the locks may be | |
+shared (e.g. read locks). This attribute takes zero or more arguments: either | |
+of lockable type or integers indexing into function parameters of lockable | |
+type. If no arguments are given, the acquired lock is implicitly ``this`` of | |
+the enclosing object. | |
+ | |
+``exclusive_trylock_function(...)`` | |
+----------------------------------- | |
+ | |
+Use ``__attribute__((exclusive_lock_function(...)))`` on a function declaration | |
+to specify that the function will try (without blocking) to acquire all listed | |
+locks exclusively. This attribute takes one or more arguments. The first | |
+argument is an integer or boolean value specifying the return value of a | |
+successful lock acquisition. The remaining arugments are either of lockable | |
+type or integers indexing into function parameters of lockable type. If only | |
+one argument is given, the acquired lock is implicitly ``this`` of the | |
+enclosing object. | |
+ | |
+``shared_trylock_function(...)`` | |
+-------------------------------- | |
+ | |
+Use ``__attribute__((shared_lock_function(...)))`` on a function declaration to | |
+specify that the function will try (without blocking) to acquire all listed | |
+locks, although the locks may be shared (e.g. read locks). This attribute | |
+takes one or more arguments. The first argument is an integer or boolean value | |
+specifying the return value of a successful lock acquisition. The remaining | |
+arugments are either of lockable type or integers indexing into function | |
+parameters of lockable type. If only one argument is given, the acquired lock | |
+is implicitly ``this`` of the enclosing object. | |
+ | |
+``unlock_function(...)`` | |
+------------------------ | |
+ | |
+Use ``__attribute__((unlock_function(...)))`` on a function declaration to | |
+specify that the function release all listed locks. This attribute takes zero | |
+or more arguments: either of lockable type or integers indexing into function | |
+parameters of lockable type. If no arguments are given, the acquired lock is | |
+implicitly ``this`` of the enclosing object. | |
+ | |
+``lock_returned(l)`` | |
+-------------------- | |
+ | |
+Use ``__attribute__((lock_returned(l)))`` on a function declaration to specify | |
+that the function returns lock ``l`` (``l`` must be of lockable type). This | |
+annotation is used to aid in resolving lock expressions. | |
+ | |
+``locks_excluded(...)`` | |
+----------------------- | |
+ | |
+Use ``__attribute__((locks_excluded(...)))`` on a function declaration to | |
+specify that the function must not be called with the listed locks. Arguments | |
+must be lockable type, and there must be at least one argument. | |
+ | |
+``exclusive_locks_required(...)`` | |
+--------------------------------- | |
+ | |
+Use ``__attribute__((exclusive_locks_required(...)))`` on a function | |
+declaration to specify that the function must be called while holding the | |
+listed exclusive locks. Arguments must be lockable type, and there must be at | |
+least one argument. | |
+ | |
+``shared_locks_required(...)`` | |
+------------------------------ | |
+ | |
+Use ``__attribute__((shared_locks_required(...)))`` on a function declaration | |
+to specify that the function must be called while holding the listed shared | |
+locks. Arguments must be lockable type, and there must be at least one | |
+argument. | |
+ | |
+Type Safety Checking | |
+==================== | |
+ | |
+Clang supports additional attributes to enable checking type safety properties | |
+that can't be enforced by C type system. Usecases include: | |
+ | |
+* MPI library implementations, where these attributes enable checking that | |
+ buffer type matches the passed ``MPI_Datatype``; | |
+* for HDF5 library there is a similar usecase as MPI; | |
+* checking types of variadic functions' arguments for functions like | |
+ ``fcntl()`` and ``ioctl()``. | |
+ | |
+You can detect support for these attributes with ``__has_attribute()``. For | |
+example: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ #if defined(__has_attribute) | |
+ # if __has_attribute(argument_with_type_tag) && \ | |
+ __has_attribute(pointer_with_type_tag) && \ | |
+ __has_attribute(type_tag_for_datatype) | |
+ # define ATTR_MPI_PWT(buffer_idx, type_idx) __attribute__((pointer_with_type_tag(mpi,buffer_idx,type_idx))) | |
+ /* ... other macros ... */ | |
+ # endif | |
+ #endif | |
+ | |
+ #if !defined(ATTR_MPI_PWT) | |
+ # define ATTR_MPI_PWT(buffer_idx, type_idx) | |
+ #endif | |
+ | |
+ int MPI_Send(void *buf, int count, MPI_Datatype datatype /*, other args omitted */) | |
+ ATTR_MPI_PWT(1,3); | |
+ | |
+``argument_with_type_tag(...)`` | |
+------------------------------- | |
+ | |
+Use ``__attribute__((argument_with_type_tag(arg_kind, arg_idx, | |
+type_tag_idx)))`` on a function declaration to specify that the function | |
+accepts a type tag that determines the type of some other argument. | |
+``arg_kind`` is an identifier that should be used when annotating all | |
+applicable type tags. | |
+ | |
+This attribute is primarily useful for checking arguments of variadic functions | |
+(``pointer_with_type_tag`` can be used in most of non-variadic cases). | |
+ | |
+For example: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ int fcntl(int fd, int cmd, ...) | |
+ __attribute__(( argument_with_type_tag(fcntl,3,2) )); | |
+ | |
+``pointer_with_type_tag(...)`` | |
+------------------------------ | |
+ | |
+Use ``__attribute__((pointer_with_type_tag(ptr_kind, ptr_idx, type_tag_idx)))`` | |
+on a function declaration to specify that the function accepts a type tag that | |
+determines the pointee type of some other pointer argument. | |
+ | |
+For example: | |
+ | |
+.. code-block:: c++ | |
+ | |
+ int MPI_Send(void *buf, int count, MPI_Datatype datatype /*, other args omitted */) | |
+ __attribute__(( pointer_with_type_tag(mpi,1,3) )); | |
+ | |
+``type_tag_for_datatype(...)`` | |
+------------------------------ | |
+ | |
+Clang supports annotating type tags of two forms. | |
+ | |
+* **Type tag that is an expression containing a reference to some declared | |
+ identifier.** Use ``__attribute__((type_tag_for_datatype(kind, type)))`` on a | |
+ declaration with that identifier: | |
+ | |
+ .. code-block:: c++ | |
+ | |
+ extern struct mpi_datatype mpi_datatype_int | |
+ __attribute__(( type_tag_for_datatype(mpi,int) )); | |
+ #define MPI_INT ((MPI_Datatype) &mpi_datatype_int) | |
+ | |
+* **Type tag that is an integral literal.** Introduce a ``static const`` | |
+ variable with a corresponding initializer value and attach | |
+ ``__attribute__((type_tag_for_datatype(kind, type)))`` on that declaration, | |
+ for example: | |
+ | |
+ .. code-block:: c++ | |
+ | |
+ #define MPI_INT ((MPI_Datatype) 42) | |
+ static const MPI_Datatype mpi_datatype_int | |
+ __attribute__(( type_tag_for_datatype(mpi,int) )) = 42 | |
+ | |
+The attribute also accepts an optional third argument that determines how the | |
+expression is compared to the type tag. There are two supported flags: | |
+ | |
+* ``layout_compatible`` will cause types to be compared according to | |
+ layout-compatibility rules (C++11 [class.mem] p 17, 18). This is | |
+ implemented to support annotating types like ``MPI_DOUBLE_INT``. | |
+ | |
+ For example: | |
+ | |
+ .. code-block:: c++ | |
+ | |
+ /* In mpi.h */ | |
+ struct internal_mpi_double_int { double d; int i; }; | |
+ extern struct mpi_datatype mpi_datatype_double_int | |
+ __attribute__(( type_tag_for_datatype(mpi, struct internal_mpi_double_int, layout_compatible) )); | |
+ | |
+ #define MPI_DOUBLE_INT ((MPI_Datatype) &mpi_datatype_double_int) | |
+ | |
+ /* In user code */ | |
+ struct my_pair { double a; int b; }; | |
+ struct my_pair *buffer; | |
+ MPI_Send(buffer, 1, MPI_DOUBLE_INT /*, ... */); // no warning | |
+ | |
+ struct my_int_pair { int a; int b; } | |
+ struct my_int_pair *buffer2; | |
+ MPI_Send(buffer2, 1, MPI_DOUBLE_INT /*, ... */); // warning: actual buffer element | |
+ // type 'struct my_int_pair' | |
+ // doesn't match specified MPI_Datatype | |
+ | |
+* ``must_be_null`` specifies that the expression should be a null pointer | |
+ constant, for example: | |
+ | |
+ .. code-block:: c++ | |
+ | |
+ /* In mpi.h */ | |
+ extern struct mpi_datatype mpi_datatype_null | |
+ __attribute__(( type_tag_for_datatype(mpi, void, must_be_null) )); | |
+ | |
+ #define MPI_DATATYPE_NULL ((MPI_Datatype) &mpi_datatype_null) | |
+ | |
+ /* In user code */ | |
+ MPI_Send(buffer, 1, MPI_DATATYPE_NULL /*, ... */); // warning: MPI_DATATYPE_NULL | |
+ // was specified but buffer | |
+ // is not a null pointer | |
+ | |
Index: docs/Tooling.html | |
=================================================================== | |
--- docs/Tooling.html (revision 169710) | |
+++ docs/Tooling.html (working copy) | |
@@ -1,120 +0,0 @@ | |
-<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" | |
- "http://www.w3.org/TR/html4/strict.dtd"> | |
-<html> | |
-<head> | |
-<title>Writing Clang Tools</title> | |
-<link type="text/css" rel="stylesheet" href="../menu.css"> | |
-<link type="text/css" rel="stylesheet" href="../content.css"> | |
-</head> | |
-<body> | |
- | |
-<!--#include virtual="../menu.html.incl"--> | |
- | |
-<div id="content"> | |
- | |
-<h1>Writing Clang Tools</h1> | |
-<p>Clang provides infrastructure to write tools that need syntactic and semantic | |
-information about a program. This document will give a short introduction of the | |
-different ways to write clang tools, and their pros and cons.</p> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="libclang"><a href="http://clang.llvm.org/doxygen/group__CINDEX.html">LibClang</a></h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>LibClang is a stable high level C interface to clang. When in doubt LibClang | |
-is probably the interface you want to use. Consider the other interfaces only | |
-when you have a good reason not to use LibClang.</p> | |
-<p>Canonical examples of when to use LibClang:</p> | |
-<ul> | |
- <li>Xcode</li> | |
- <li>Clang Python Bindings</li> | |
-</ul> | |
-<p>Use LibClang when you...</p> | |
-<ul> | |
- <li>want to interface with clang from other languages than C++</li> | |
- <li>need a stable interface that takes care to be backwards compatible</li> | |
- <li>want powerful high-level abstractions, like iterating through an AST | |
-with a cursor, and don't want to learn all the nitty gritty details of Clang's | |
-AST.</li> | |
-</ul> | |
-<p>Do not use LibClang when you...</p> | |
-<ul> | |
- <li>want full control over the Clang AST</li> | |
-</ul> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="clang-plugins"><a href="ClangPlugins.html">Clang Plugins</a></h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>Clang Plugins allow you to run additional actions on the AST as part of | |
-a compilation. Plugins are dynamic libraries that are loaded at runtime by | |
-the compiler, and they're easy to integrate into your build environment.</p> | |
-<p>Canonical examples of when to use Clang Plugins:</p> | |
-<ul> | |
- <li>special lint-style warnings or errors for your project</li> | |
- <li>creating additional build artifacts from a single compile step</li> | |
-</ul> | |
-<p>Use Clang Plugins when you...</p> | |
-<ul> | |
- <li>need your tool to rerun if any of the dependencies change</li> | |
- <li>want your tool to make or break a build</li> | |
- <li>need full control over the Clang AST</li> | |
-</ul> | |
-<p>Do not use Clang Plugins when you...</p> | |
-<ul> | |
- <li>want to run tools outside of your build environment</li> | |
- <li>want full control on how Clang is set up, including mapping of in-memory | |
- virtual files</li> | |
- <li>need to run over a specific subset of files in your project which is not | |
- necessarily related to any changes which would trigger rebuilds</li> | |
-</ul> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="libtooling"><a href="LibTooling.html">LibTooling</a></h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>LibTooling is a C++ interface aimed at writing standalone tools, as well as | |
-integrating into services that run clang tools.</p> | |
-<p>Canonical examples of when to use LibTooling:</p> | |
-<ul> | |
- <li>a simple syntax checker</li> | |
- <li>refactoring tools</li> | |
-</ul> | |
-<p>Use LibTooling when you...</p> | |
-<ul> | |
- <li>want to run tools over a single file, or a specific subset of files, | |
- independently of the build system</li> | |
- <li>want full control over the Clang AST</li> | |
- <li>want to share code with Clang Plugins</li> | |
-</ul> | |
-<p>Do not use LibTooling when you...</p> | |
-<ul> | |
- <li>want to run as part of the build triggered by dependency changes</li> | |
- <li>want a stable interface so you don't need to change your code when the | |
- AST API changes</li> | |
- <li>want high level abstractions like cursors and code completion out of the | |
- box</li> | |
- <li>do not want to write your tools in C++</li> | |
-</ul> | |
- | |
-<!-- ======================================================================= --> | |
-<h2 id="clang-tools"><a href="ClangTools.html">Clang Tools</a></h2> | |
-<!-- ======================================================================= --> | |
- | |
-<p>These are a collection of specific developer tools built on top of the | |
-LibTooling infrastructure as part of the Clang project. They are targeted at | |
-automating and improving core development activities of C/C++ developers.</p> | |
-<p>Examples of tools we are building or planning as part of the Clang | |
-project:</p> | |
-<ul> | |
- <li>Syntax checking (clang-check)</li> | |
- <li>Automatic fixing of compile errors (clangc-fixit)</li> | |
- <li>Automatic code formatting</li> | |
- <li>Migration tools for new features in new language standards</li> | |
- <li>Core refactoring tools</li> | |
-</ul> | |
- | |
-</div> | |
-</body> | |
-</html> | |
- |
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