d3lm/CLang Optimizations.md

## CLang Optimizations.md

      
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              CLang Optimizations.md
            
          
    CLang optimizations on Mac OSX

Version:
Apple LLVM version 6.0 (clang-600.0.57) (based on LLVM 3.5svn)
Target: x86_64-apple-darwin14.1.0
Thread model: posix

This was made with commands:
echo 'int;' | clang -xc -O0    - -o /dev/null -\#\#\#
echo 'int;' | clang -xc -O1    - -o /dev/null -\#\#\#
echo 'int;' | clang -xc -O2    - -o /dev/null -\#\#\#
echo 'int;' | clang -xc -O3    - -o /dev/null -\#\#\#
echo 'int;' | clang -xc -Ofast - -o /dev/null -\#\#\#
echo 'int;' | clang -xc -Os    - -o /dev/null -\#\#\#
echo 'int;' | clang -xc -Oz    - -o /dev/null -\#\#\#


-O0 means "no optimization": this level compiles the fastest and generates the most debuggable code.  It enable -mrelax-all option.
-O1 somewhere between -O0 and -O2.
-O2 moderate level of optimization which enables most optimizations.
-O3 is like -O2 except that it enables optimizations that take longer to perform or that may generate larger code (in an attempt to make the program run faster).
-Ofast enable -O3, with other aggressive optimizations that may violate strict compliance with language standards.  It speedup math calculations.
-Os is like -O2 with extra optimizations to reduce code size.
-Oz is like -Os, but try to minimise even more the code size.


Option
-O0
-O1
-O2
-O3
-Ofast
-Os
-Oz
Description


-triple x86_64-apple-macosx10.10.0
✅
✅
✅
✅
✅
✅
✅
Specify target triple


-emit-obj
✅
✅
✅
✅
✅
✅
✅
Emit native object files


-mrelax-all
✅
❌
❌
❌
❌
❌
❌
(integrated-as) Relax all machine instructions


-disable-free
✅
✅
✅
✅
✅
✅
✅
Disable freeing of memory on exit


-disable-llvm-verifier
✅
✅
✅
✅
✅
✅
✅
Don't run the LLVM IR verifier pass


-mrelocation-model pic
✅
✅
✅
✅
✅
✅
✅
The relocation model to use


-pic-level 2
✅
✅
✅
✅
✅
✅
✅
Value for __PIC__


-mdisable-fp-elim
✅
✅
✅
✅
✅
✅
✅
Disable frame pointer elimination optimization


-menable-no-infs
❌
❌
❌
❌
✅
❌
❌
Allow optimization to assume there are no infinities.


-menable-no-nans
❌
❌
❌
❌
✅
❌
❌
Allow optimization to assume there are no NaNs.


-menable-unsafe-fp-math
❌
❌
❌
❌
✅
❌
❌
Allow unsafe floating-point math optimizations which may decrease precision


-ffp-contract=fast
❌
❌
❌
❌
✅
❌
❌
Form fused FP ops (e.g. FMAs): fast (everywhere) OR on (according to FP_CONTRACT pragma, default) OR off (never fuse)


-ffast-math
❌
❌
❌
❌
✅
❌
❌
Enable the frontend's 'fast-math' mode. This has no effect on optimizations, but provides a preprocessor macro __FAST_MATH__ the same as GCC's -ffast-math flag


-masm-verbose
✅
✅
✅
✅
✅
✅
✅
Generate verbose assembly output


-munwind-tables
✅
✅
✅
✅
✅
✅
✅
Generate unwinding tables for all functions


-target-cpu core2
✅
✅
✅
✅
✅
✅
✅
Target a specific cpu type


-target-linker-version 241.9
✅
✅
✅
✅
✅
✅
✅
Target linker version


-resource-dir
✅
✅
✅
✅
✅
✅
✅
The directory which holds the compiler resource files


-fdebug-compilation-dir
✅
✅
✅
✅
✅
✅
✅
The compilation directory to embed in the debug info.


-ferror-limit 19
✅
✅
✅
✅
✅
✅
✅
Set the maximum number of errors to emit before stopping (0 = no limit).


-fmessage-length 117
✅
✅
✅
✅
✅
✅
✅
Format message diagnostics so that they fit within N columns or fewer, when possible.


-stack-protector 1
✅
✅
✅
✅
✅
✅
✅
Enable stack protectors


-mstackrealign
✅
✅
✅
✅
✅
✅
✅
Force realign the stack at entry to every function


-fblocks
✅
✅
✅
✅
✅
✅
✅
Enable the 'blocks' language feature


-fobjc-runtime
✅
✅
✅
✅
✅
✅
✅
Specify the target Objective-C runtime kind and version


-fencode-extended-block-signature
✅
✅
✅
✅
✅
✅
✅
enable extended encoding of block type signature


-fdiagnostics-show-option
✅
✅
✅
✅
✅
✅
✅
Print option name with mappable diagnostics


-fcolor-diagnostics
✅
✅
✅
✅
✅
✅
✅
Use colors in diagnostics


-vectorize-loops
❌
❌
✅
✅
✅
✅
❌
Run the Loop vectorization passes


-vectorize-slp
✅
✅
✅
✅
✅
✅
✅
Run the SLP vectorization passes
Option	-O0	-O1	-O2	-O3	-Ofast	-Os	-Oz	Description
-triple x86_64-apple-macosx10.10.0	✅	✅	✅	✅	✅	✅	✅	Specify target triple
-emit-obj	✅	✅	✅	✅	✅	✅	✅	Emit native object files
-mrelax-all	✅	❌	❌	❌	❌	❌	❌	(integrated-as) Relax all machine instructions
-disable-free	✅	✅	✅	✅	✅	✅	✅	Disable freeing of memory on exit
-disable-llvm-verifier	✅	✅	✅	✅	✅	✅	✅	Don't run the LLVM IR verifier pass
-mrelocation-model pic	✅	✅	✅	✅	✅	✅	✅	The relocation model to use
-pic-level 2	✅	✅	✅	✅	✅	✅	✅	Value for `__PIC__`
-mdisable-fp-elim	✅	✅	✅	✅	✅	✅	✅	Disable frame pointer elimination optimization
-menable-no-infs	❌	❌	❌	❌	✅	❌	❌	Allow optimization to assume there are no infinities.
-menable-no-nans	❌	❌	❌	❌	✅	❌	❌	Allow optimization to assume there are no NaNs.
-menable-unsafe-fp-math	❌	❌	❌	❌	✅	❌	❌	Allow unsafe floating-point math optimizations which may decrease precision
-ffp-contract=fast	❌	❌	❌	❌	✅	❌	❌	Form fused FP ops (e.g. FMAs): fast (everywhere) OR on (according to FP_CONTRACT pragma, default) OR off (never fuse)
-ffast-math	❌	❌	❌	❌	✅	❌	❌	Enable the frontend's 'fast-math' mode. This has no effect on optimizations, but provides a preprocessor macro `__FAST_MATH__` the same as GCC's -ffast-math flag
-masm-verbose	✅	✅	✅	✅	✅	✅	✅	Generate verbose assembly output
-munwind-tables	✅	✅	✅	✅	✅	✅	✅	Generate unwinding tables for all functions
-target-cpu core2	✅	✅	✅	✅	✅	✅	✅	Target a specific cpu type
-target-linker-version 241.9	✅	✅	✅	✅	✅	✅	✅	Target linker version
-resource-dir	✅	✅	✅	✅	✅	✅	✅	The directory which holds the compiler resource files
-fdebug-compilation-dir	✅	✅	✅	✅	✅	✅	✅	The compilation directory to embed in the debug info.
-ferror-limit 19	✅	✅	✅	✅	✅	✅	✅	Set the maximum number of errors to emit before stopping (0 = no limit).
-fmessage-length 117	✅	✅	✅	✅	✅	✅	✅	Format message diagnostics so that they fit within N columns or fewer, when possible.
-stack-protector 1	✅	✅	✅	✅	✅	✅	✅	Enable stack protectors
-mstackrealign	✅	✅	✅	✅	✅	✅	✅	Force realign the stack at entry to every function
-fblocks	✅	✅	✅	✅	✅	✅	✅	Enable the 'blocks' language feature
-fobjc-runtime	✅	✅	✅	✅	✅	✅	✅	Specify the target Objective-C runtime kind and version
-fencode-extended-block-signature	✅	✅	✅	✅	✅	✅	✅	enable extended encoding of block type signature
-fdiagnostics-show-option	✅	✅	✅	✅	✅	✅	✅	Print option name with mappable diagnostics
-fcolor-diagnostics	✅	✅	✅	✅	✅	✅	✅	Use colors in diagnostics
-vectorize-loops	❌	❌	✅	✅	✅	✅	❌	Run the Loop vectorization passes
-vectorize-slp	✅	✅	✅	✅	✅	✅	✅	Run the SLP vectorization passes