Another LLVM JIT - Loading variable from memory clang++-mp-3.3 `llvm-config --cppflags --ldflags --libs core jit X86` jit2.cpp

jit2.cpp

#include <iostream>
#include <cstdint>
#include <string>

#include "llvm/ExecutionEngine/JIT.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Module.h"
#include "llvm/PassManager.h"
#include "llvm/Support/TargetSelect.h"
#include "llvm/Analysis/Verifier.h"

using namespace llvm;

int main(int argc, char * argv[]) {
    InitializeNativeTarget();

    /* LLVM Global Context */
    LLVMContext & ctx = getGlobalContext();

    /* Module */
    Module * module = new Module("MyModule", ctx);

    /* IRBuilder */
    IRBuilder<> builder(ctx);

    /* Create execution engine */
    std::string err_str;
    CodeGenOpt::Level opt = CodeGenOpt::Default;
    ExecutionEngine * engine = ExecutionEngine::createJIT(module, &err_str,
                                                          0, opt);
    if (!engine) {
        std::cerr << "Could not create ExecutionEngine:"
                  << err_str << std::endl;
        return 1;
    }

    /* LLVM Type of int64_t* */
    PointerType * int64_ptr_ty = Type::getInt64PtrTy(ctx, false);

    /* LLVM Type of int64_t */
    IntegerType * int64_ty = Type::getInt64Ty(ctx);

    /* Create prototype of result function - int64_t() */
    std::vector<Type *> arguments;
    FunctionType * proto = FunctionType::get(int64_ty, arguments, false);
 
    /* Create function body */
    Function * fce = Function::Create(proto, Function::ExternalLinkage,
                                      "MyFunction", module);
    BasicBlock * bb = BasicBlock::Create(ctx, "entry", fce);
 
    /* Point builder to add instructions to function body */
    builder.SetInsertPoint(bb);
 
    /* Actual value to return */
    int64_t value = 765;

    /* Address of value */
    Value * addr = ConstantInt::get(int64_ty, APInt(64, (uint64_t)&value));

    /* LLVM Pointer to int64_t value */
    Value * value_ptr = builder.CreateIntToPtr(addr,
                                               int64_ptr_ty,
                                               "int_to_ptr_cast");

    /* LLVM Value */
    Value * v = builder.CreateLoad(value_ptr, "load_value");

    /* Return value */
    builder.CreateRet(v);
 
    /* Function pass manager */
    FunctionPassManager pass_manager(module);
 
    /* Add data layout */
    pass_manager.add(new DataLayout(*engine->getDataLayout()));
    pass_manager.doInitialization();
 
    /* Do optimizations */
    pass_manager.run(*fce);

    /* JIT it */
    void * fce_ptr = engine->getPointerToFunction(fce);
    int64_t (*fce_typed_ptr)() = (int64_t(*)())fce_ptr;
 
    /* Excute JITed function */
    std::cout << "Result: " << (*fce_typed_ptr)()
              << std::endl << std::endl;
 
    /* Dump LLVM IR */
    std::cout << "LLVM IR dump: " << std::endl;
    module->dump();
 
    return 0;
}