Abstract Syntax Tree Optimizations - GNU Project - Free Software Foundation (FSF) Abstract Syntax Tree Optimizations
This page describes ongoing work to improve GCC's tree based optimizations. There is a branch in CVS called, ast-optimizer-branch, which is available to experiment with these optimizers. As these stabilize, they can be submitted for review onto the mainline development tree. Please contact Nathan Sidwell, , if you want to contribute.
Background & Rationale
GCC, in common with many other compilers, has more than one internal representation of a program. The main ones are trees and RTL. The trees, (or formally abstract syntax trees - ASTs) are generated during parsing, and are close to the source language semantics. The RTL is generated in the back end, and is close to the generated assembly code. Ideally, the AST would contain all the semantic information of the source program.
Historically, GCC generated RTL one statement at a time, so the AST did not stay around very long. This has changed with 'function at a time' compilation (Inliner), which both C and C frontends now implement. With the AST for complete functions, and the additional semantic information they contain, the opportunity for new optimizations presents itself.