[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 << "
";                                                         
    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.