example of using llvm IR library and JIT system

sum-jit.cpp

#include <string>
#include <iostream>

#include "llvm/ExecutionEngine/JIT.h"

#include "llvm/ADT/OwningPtr.h"
#include "llvm/Bitcode/ReaderWriter.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/ManagedStatic.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/system_error.h"
#include "llvm/Support/TargetSelect.h"

using namespace llvm;

int main()
{
    llvm::InitializeNativeTarget();

    // read byte-code from file
    llvm::OwningPtr<llvm::MemoryBuffer> Buffer;
    if (llvm::MemoryBuffer::getFile("./sum.bc", Buffer))
    {
        llvm::errs() << "sum.bc not found\n";
        return -1;
    }

    // generate corresponding LLVM module
    llvm::LLVMContext Context;
    std::string ErrorMessage;
    llvm::Module* M = llvm::ParseBitcodeFile(Buffer.get(), Context, &ErrorMessage);
    if (! M)
    {
        llvm::errs() << ErrorMessage << "\n";
        return -1;
    }
  
    // create JIT execution engine and setup JIT, no function is complied yet
    llvm::OwningPtr<llvm::ExecutionEngine> EE(llvm::EngineBuilder(M).create());

    // retrieve the Function IR object that represents sum
    llvm::Function* SumFn = M->getFunction("sum");

    // trigger JIT compilation
    int(*Sum)(int, int) = (int(*)(int, int))EE->getPointerToFunction(SumFn);

    // call the original sum function via the JIT-compiled function
    int res = Sum(4, 5);
    llvm::outs() << "Sum result: " << res << "\n";

    // release the execution engine allocated memory that holds the function code
    EE->freeMachineCodeForFunction(SumFn);
    llvm::llvm_shutdown();

    return 0;
}