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Re: Analyzing Optimization: What's New in 3.4?
- From: neroden at twcny dot rr dot com (Nathanael Nerode)
- To: gcc at gcc dot gnu dot org, coyote at coyotegulch dot com
- Date: Tue, 12 Aug 2003 02:32:17 -0400
- Subject: Re: Analyzing Optimization: What's New in 3.4?
>What about -fnew-ra, -ftracer, and other options rarely discussed (and
>probably unknown to most gcc users)?
-fnew-ra is still experimental because it still fails on code which the
old register allocator allocated Just Fine. It also doesn't usually
give better performance at the moments.
Its purpose is mainly to improve the future maintainability of GCC,
since the current regalloc/reload mishmash is very, very, very hard to
maintain.
You might like to try Geoff Keating's intermodule optimizations.
They are enabled in some funny way which I can't remember. :-)
There's a profiling-directed branch prediction option which I can never
remember how to use, but which seems to really do wonders.
Be sure to mess around with -fschedule-insns and -fschedule-insns2.
It seems that on many machines -fschedule-insns creates substantially
*worse* code (so use -fno-schedule-insns) and -fschedule-insns2 creates
slightly better code, but all four combinations should be tried. ;-)
--
Nathanael Nerode <neroden at gcc.gnu.org>
http://home.twcny.rr.com/nerode/neroden/fdl.html