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Re: Optimal Optimizations: A Very Preliminary Report
- From: neroden at twcny dot rr dot com (Nathanael Nerode)
- To: gcc at gcc dot gnu dot org
- Date: Tue, 12 Aug 2003 12:24:59 -0400
- Subject: Re: Optimal Optimizations: A Very Preliminary Report
Diego Novillo wrote:
>As I see it, the problem has at least three dimensions:
> 1. Selection of optimization options
> 2. Ordering of the different passes
> 3. Programs used as benchmarks
>Ideally, one would explore that 3 dimensional space and cut slices to
>stick in the different -Ox. GCC will let you play with #1 (to a
>certain extent) and #3, but you cannot change #2.
With some notable exceptions, such as -fschedule-insns vs.
(Incidentally, the evidence for that particular case indicates that
-fschedule-insns should be abandoned entirely, while -fschedule-insns2
should be standard.)
Actually, #2 is an interesting point: 'common sense' and
reasoning actually do a pretty good job of determining the correct
order for passes. (For example, I guessed before seeing any data
that insn scheduling ought to be post-regalloc, and I appear to have
been correct.) Common sense and reasoning don't seem to do such a good
job at determing what passes are worthwhile (#1) or what programs are
good benchmarks (#3).
Nathanael Nerode <neroden at gcc.gnu.org>