[LLVMdev] Some questions about building an LLVM frontend

[Chris Lattner]

On Aug 24, 2007, at 7:02 PM, Talin wrote:

> I've been working some more on my front-end, incorporating the advice
> from your previous email.
>
> I've had some success, in that I can generate a Module object,  
> populated
> it with functions and instructions, and print out the resulting  
> LLVM IR.

Great!

> But I'm still a little puzzled on how to connect the front end with
> LLVM's backend code generator, I can't seem to figure out how to  
> run the
> various optimization and code generation passes.

You need to set up a passmanager or two, populate them with the  
passes you want, then tell them to run on the code, when appropriate.

> The one example that seems close to what I want is the llc.cpp source
> file; But when I try to do the same thing in my code, I find that the
> TargetMachineRegistry is empty; And yet I see no code in llc.cpp that
> initializes this, nor do I see #includes or Makefile dependencies  
> in the
> llc project that would do this implicitly.

The best example here is llvm-gcc.  In particular, the llvm- 
backend.cpp file contains the top-level code that sets up the  
optimization pipeline and the code generator, and is the one that  
runs it at various times.

-Chris