AST optimizer in C++?

[Pop Sébastian <pop at gauvain dot u-strasbg dot fr>]

Hi Chris,

On Thu, Aug 22, 2002 at 03:53:54PM -0500, Chris Lattner wrote:
> 
> > Go right ahead.  All you need is a new branch and some free time.  I
> > would personally suggest following some of the design and implementation
> > ideas from SUIF and/or Sage++.  They are kind of neat.
> 
> As long as we are plugging compiler infrastructures, I thought I might
> mention my own project LLVM: http://llvm.cs.uiuc.edu/
> 
I had a look at the project, and I'm interested to have a look at the sources
(if it's possible).

> It's also completely written in C++ (G++ 3.2), uses a GCC->LLVM frontend,
> is SSA based, open-source, and has some interesting technology available
> in it.  The LLVM instruction set is roughly equivalent to SIMPLE
> (http://llvm.cs.uiuc.edu/docs/LangRef.html).
> 
> A few of the nify things LLVM provides are the modular pass system:
> http://llvm.cs.uiuc.edu/docs/WritingAnLLVMPass.html
> strong infrastructure for interprocedural optimizations, linktime, and
> runtime optimizations, etc.  The infrastructure is _very_ fast.
> 
> Additionally, because it uses C++ and the STL throughout, writing
> transformations is quite simple.  For example, LICM and GCSE are each
> just a couple hundred lines of code (which are mostly comments):
> 
> http://llvm/doxygen/LICM_8cpp-source.html
> http://llvm/doxygen/GCSE_8cpp-source.html
> 
> If you have any questions about LLVM or would like to discuss compiler
> architecture, I'd be more than happy to participate.
> 
After what I (quickly) read from the web page you use gcc's front-ends.
My questions are:
- Do you have a class hierarchy for representing statements and expressions?
- Is it possible to generate GCC trees after your optimizations?  (and then
generate RTL by passing these trees to the RTL-translator...)


In fact what I want for gcc is an AST optimizer that could be built independently
of gcc's front-ends.  This optimizer takes as input SIMPLE trees and its output 
is again gcc trees (a subset of SIMPLE, or even a superset of SIMPLE if we decide 
to promote some stmts/exprs to a higher level during optimization).  

The overall schema could be:

(GCC front-ends) -> (GENERIC trees) -> [(SIMPLE trees) -> (AST Optimizer)] -> 
-> (RTL conversion) -> (Code generation)

with optional components in "-> [...] ->".  These components are not mandatory 
for building the GCC compiler.  They could be built apart once the g++ compiler 
is available.  The AST optimizer could be loaded from a .so file (as in open64 
compiler) and thus avoiding to grow too much the size of the executable when 
AST optimization is not needed.