Re: LLVM as a gcc plugin?

[Chris Lattner <clattner at apple dot com>]

On Jun 4, 2009, at 3:20 AM, Steven Bosscher wrote:

> On Thu, Jun 4, 2009 at 12:14 PM, Rafael Espindola <espindola@google.com 
> > wrote:
> > > I'd love to see this, but I can't contribute to it directly.  I  
> > > think the
> > > plugin interfaces would need small extensions, but there are no  
> > > specific
> > > technical issues preventing it from happening.  LLVM has certainly
> > > progressed a lot since that (really old) email went out :)
> >
> > I can help a bit.

> Aren't LLVM and GCC doing just fine as
> competing compilers?

I'm not sure what you mean, LLVM and GCC are two completely different  
things.  LLVM is an infrastructure for building compilers, GCC is an  
instance of a compiler.  Combining LLVM with GCC gives LLVM-GCC  
(another instance of a compiler), which adds new capabilities to GCC  
that many users find useful.  These include things such as cross- 
language LTO support (for C, c++, fortran, etc), JIT compilation,  
better performance in some scenarios, etc.

> Excuse me if this is a stupid question, but eh -- why would you want
> to make an LLVM plugin?

There are multiple answers to this question.  The most obvious one is  
that the current version of llvm-gcc is stuck on GCC 4.2, and 4.2  
lacks a number of improvements the fortran and ada front-ends and  
runtimes.  It would be straight-forward to forward port the patches to  
gcc mainline, but presumably implementing llvm-gcc in terms of plugins  
would result in something that has easier maintenance (this remains to  
be seen of course).

-Chris