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Re: Optimal Optimizations: A Very Preliminary Report
- From: <tm_gccmail at mail dot kloo dot net>
- To: Nathanael Nerode <neroden at twcny dot rr dot com>
- Cc: gcc at gcc dot gnu dot org
- Date: Tue, 12 Aug 2003 11:28:08 -0700 (PDT)
- Subject: Re: Optimal Optimizations: A Very Preliminary Report
On Tue, 12 Aug 2003, Nathanael Nerode wrote:
> 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.)
Please don't suggest abandoning -fschedule-insns unless you understand the
full intricacies of the situation and have a viable alternative.
The current problem with sched1 isn't the concept of scheduling before
register allocation; rather, it's allowing the scheduler unrestrained
freedom to move instructions before register allocation which can raise
register pressure unnecessarily. People are working on a solution for this