[llvm] Call the LLVM Jit from c program

stackoverflow: http://stackoverflow.com/questions/1838304/call-the-llvm-jit-from-c-program

Another trial under llvm 3.2;

In prepared IR "tst.ll", code:

; ModuleID = 'tst.bc'              

define i32 @add1(i32 %AnArg) {
EntryBlock:
  %0 = add i32 1, %AnArg
  ret i32 %0
}                                  

define i32 @foo() {
EntryBlock:
  %0 = tail call i32 @add1(i32 10)
  ret i32 %0
}

run " llvm-as tst.ll " to create the asm file tst.bc

then the caller programe:

#include <string>
#include <memory>
#include <iostream>                                                                       

#include <llvm/LLVMContext.h>
#include <llvm/Support/TargetSelect.h>
#include <llvm/Bitcode/ReaderWriter.h>
#include <llvm/ExecutionEngine/ExecutionEngine.h>
#include <llvm/Module.h>
#include <llvm/Support/MemoryBuffer.h>
#include <llvm/ExecutionEngine/JIT.h>
#include <llvm/Support/system_error.h>                                                    

using namespace std;
using namespace llvm;                                                                     

int main()
{
    InitializeNativeTarget();
    llvm_start_multithreaded();
    LLVMContext context;
    string error;                                                                         

    OwningPtr<MemoryBuffer> file_buffer;
    MemoryBuffer::getFile("tst.bc", file_buffer);
    Module *m = ParseBitcodeFile(file_buffer.get(), context, &error);                     

    ExecutionEngine *ee = ExecutionEngine::create(m);                                     

    Function* func = ee->FindFunctionNamed("foo");                                        

    typedef int (*PFN)();
    PFN pfn = reinterpret_cast<PFN>(ee->getPointerToFunction(func));
    int x = pfn();
    cout << "~~~  " << x << "\n";
    delete ee;                                                                            

}

In the above example, IR codes are load from a file. In more dymanic usage, we could construct the IR code as a string according to input "query" type. Then compile the IR to bitcode on the fly.