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Re: GCC 3.3 compile speed regression - AN ANSWER
- From: Matt Austern <austern at apple dot com>
- To: Linus Torvalds <torvalds at transmeta dot com>
- Cc: jsm28 at cam dot ac dot uk, gcc at gcc dot gnu dot org
- Date: Tue, 11 Feb 2003 19:33:17 -0800
- Subject: Re: GCC 3.3 compile speed regression - AN ANSWER
On Tuesday, February 11, 2003, at 04:08 PM, Linus Torvalds wrote:
The thing is, if you want to make gcc faster, you have to bite the
bullet and throw out code that doesn't perform well. And you have to
_remove_ phases of optimization, instead of adding new ones. Having
different phases where you operate on different kinds of data
structures
(ie tree -> ssa -> rtl) is just fundamentally slow, as you have to
marshall the data into the right format for the next phase (which is
likely bad for caches too).
All of my measurements suggest that improving the speed of optimization
phases is irrelevant. What's slow is the front end: parsing and
semantic analysis. -O0 compilations are slow, not just -O3.
There are compilers that do lots of tricky optimizations, where you pay
in compile speed for that last 0.1% improvement in SPEC numbers. gcc
is not one of them.
--Matt