LLVM C++ Program Compilation - c++

Question

Hi I have written a simple C++ code with the LLVM Api
#include <stdio.h>
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/IRBuilder.h"
int main()
{
llvm::LLVMContext& context = llvm::getGlobalContext();
llvm::Module* module = new llvm::Module("top", context);
llvm::IRBuilder<> builder(context);
module->dump( );
}
How do i compile this to get the LLVM IR file?
Thanks for any help

Answer 1

Compilation of the program itself to a native machine code binary is straightforward. On a Unix platform:
$ clang++ <c++ file> `llvm-config --cppflags --ldflags --libs core`
llvm-config is a tool providing the necessary compilation flags to include certain components of the llvm framework. In your case, it seems you only need the core component.
Adding the -v parameter to the command line requires clang to output all the used commands. Adding -S -emit-llvm (both parameters must be used together) will make it output an llvm IR translation of the source
$ clang++ -v file.cpp `llvm-config --cppflags --ldflags --libs core` -S -emit-llvm
The resulting file.s may be then directly interpreted with lli or further compiled to bitcode using llvm-as, which renders a .bc file.
$ llvm-as file.s
The same lli will gladly run that file as well:
$ lli file.s.bc
Running or interpreting any of these resulting files (llvm IR, bitcode or native program), will of course yield the same result, the dumping of the llvm IR code of the module top defined in your program (which is empty).
Documentation:
llvm-config
llvm-as
lli

Answer 2

The easiest thing to do is to forward the output into a file and then process that so something like this(assuming the compiled code above is compiled into an executable name 'parser'):
./parser >> test.ll
llvm-as test.ll
llc test.bc
clang -o test test.s
Hopefully that helps!
As a side note I have my parser to this internally via system() calls and command line options, so that may be something you want to think about as well^^