Editing GNU Compiler Collection (section)

=== Optimization ===
Optimization can occur during any phase of compilation; however, the bulk of optimizations are performed after the syntax and [[Semantic analysis (compilers)|semantic analysis]] of the front end and before the [[Code generation (compiler)|code generation]] of the back end; thus a common, though somewhat self-contradictory, name for this part of the compiler is the "middle end."

The exact set of GCC optimizations varies from release to release as it develops, but includes the standard algorithms, such as [[loop optimization]], [[jump threading]], [[common subexpression elimination]], [[instruction scheduling]], and so forth. The [[Register transfer language|RTL]] optimizations are of less importance with the addition of global SSA-based optimizations on [[GIMPLE]] trees,<ref>{{cite web|url=http://www.redhat.com/magazine/002dec04/features/gcc/|title=From Source to Binary: The Inner Workings of GCC|last=Novillo|first=Diego|work=[[Red Hat#Opensource.com|Red Hat Magazine]]|date=December 2004|url-status=dead|archive-url=https://web.archive.org/web/20090401215553/http://www.redhat.com/magazine/002dec04/features/gcc/|archive-date=April 1, 2009|df=mdy-all}}</ref> as RTL optimizations have a much more limited scope, and have less high-level information.

Some of these optimizations performed at this level include [[dead-code elimination]], [[partial-redundancy elimination]], [[global value numbering]], [[sparse conditional constant propagation]], and [[scalar replacement of aggregates]]. Array dependence based optimizations such as [[automatic vectorization]] and [[automatic parallelization]] are also performed. [[Profile-guided optimization]] is also possible.<ref>{{Cite web|url=https://gcc.gnu.org/install/build.html#TOC4|title=Installing GCC: Building - GNU Project|website=gcc.gnu.org|access-date=July 25, 2016|archive-date=August 22, 2023|archive-url=https://web.archive.org/web/20230822141635/http://gcc.gnu.org/install/build.html#TOC4|url-status=live}}</ref>