Call LLVM Jit from c program - llvm

Question

I have generated a bc file with the online compiler on llvm.org, and I would like to know if it is possible to load this bc file from a c or c++ program, execute the IR in the bc file with the llvm jit (programmatically in the c program), and get the results.
How can I accomplish this?

Answer 1

Here's some working code based on Nathan Howell's:
#include <string>
#include <memory>
#include <iostream>
#include <llvm/LLVMContext.h>
#include <llvm/Target/TargetSelect.h>
#include <llvm/Bitcode/ReaderWriter.h>
#include <llvm/ExecutionEngine/ExecutionEngine.h>
#include <llvm/ModuleProvider.h>
#include <llvm/Support/MemoryBuffer.h>
#include <llvm/ExecutionEngine/JIT.h>
using namespace std;
using namespace llvm;
int main()
{
InitializeNativeTarget();
llvm_start_multithreaded();
LLVMContext context;
string error;
Module *m = ParseBitcodeFile(MemoryBuffer::getFile("tst.bc"), context, &error);
ExecutionEngine *ee = ExecutionEngine::create(m);
Function* func = ee->FindFunctionNamed("main");
typedef void (*PFN)();
PFN pfn = reinterpret_cast<PFN>(ee->getPointerToFunction(func));
pfn();
delete ee;
}
One oddity was that without the final include, ee is NULL. Bizarre.
To generate my tst.bc, I used http://llvm.org/demo/index.cgi and the llvm-as command-line tool.

Answer 2

This should (more or less) work using LLVM 2.6. It looks like there are some more helper functions in SVN to create a lazy ModuleProvider on top of a bitcode file. I haven't tried compiling it though, just glued together some bits from one of my JIT applications.
#include <string>
#include <memory>
#include <llvm/Bitcode/ReaderWriter.h>
#include <llvm/ExecutionEngine/ExecutionEngine.h>
#include <llvm/ModuleProvider.h>
#include <llvm/Support/MemoryBuffer.h>
#include <llvm/ExecutionEngine/JIT.h>
using namespace std;
using namespace llvm;
int main()
{
InitializeNativeTarget();
llvm_start_multithreaded();
LLVMContext context;
string error;
auto_ptr<MemoryBuffer> buffer(MemoryBuffer::getFile("bitcode.bc"));
auto_ptr<Module> module(ParseBitcodeFile(buffer.get(), context, &error));
auto_ptr<ModuleProvider> mp(new ExistingModuleProvider(module));
module.release();
auto_ptr<ExecutionEngine> ee(ExecutionEngine::createJIT(mp.get(), &error));
mp.release();
Function* func = ee->getFunction("foo");
typedef void (*PFN)();
PFN pfn = reinterpret_cast<PFN>(ee->getPointerToFunction(func));
pfn();
}

Answer 3

From the command line, you can use the LLVM program lli to run a bc file. If the file is in LLVM assembly language, you'll have to run llvm-as on it first to create a binary bitcode file.
It is easy to do this from C. I'd recommend you look at the extensive LLVM documentation: http://llvm.org/docs
The LLVM irc channel, which has a link on that page, is full of very knowledgeable people that are willing to answer questions.
Sorry for the indirect answer. I use LLVM extensively, but I do direct code generation not just in time compliation.