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Re: Performance regression
- From: Dale Johannesen <dalej at apple dot com>
- To: Roger Sayle <roger at eyesopen dot com>
- Cc: Dale Johannesen <dalej at apple dot com>, Jim Wilson <wilson at redhat dot com>, gcc at gcc dot gnu dot org, gcc-patches at gcc dot gnu dot org
- Date: Wed, 25 Sep 2002 10:24:52 -0700
- Subject: Re: Performance regression
On Wednesday, September 25, 2002, at 08:44 AM, Roger Sayle wrote:
On 25 Sep 2002, Jim Wilson wrote:
This has been discussed many times before. The only way to avoid
performance
loss from changing the semantics of LOAD_EXTEND_OP is to add new
optimizer
support for sign/zero extend operations.
Since we went ahead with the LOAD_EXTEND_OP change to fix optimizer
bugs,
it would be useful if someone was looking into the new optimization
support
we need. Maybe it can go on the projects list? Add support for
optimizing
sign/zero extend operations. Some problems can be fixed by being
careful
in the md file, but some problems can be solved only with an
optimization
pass that is designed to optimize away redundant sign/zero extend
operations.
I'm more than happy to work on adding some sign/zero extend
optimizations
to the GCC's RTL optimizers. I just didn't want to clash with Dale, if
Apple wanted to start work on it straight away.
At the moment this isn't showing up as a big performance hit, so I
doubt we'll
be working on it soon. As always that could change.