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Re: [PATCH] Disable CSE skip-blocks
- From: Paolo Bonzini <paolo dot bonzini at lu dot unisi dot ch>
- To: Roger Sayle <roger at eyesopen dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Sun, 29 Oct 2006 19:33:45 +0100
- Subject: Re: [PATCH] Disable CSE skip-blocks
- References: <Pine.LNX.email@example.com>
Thanks Roger for expressing what Steven and I have been stating for
I have faith than when complete the resulting
objects will be smaller and faster. It doesn't make much sense
to enquire about "SPEC with -fno-cse-skip-blocks" because it may
be unreasonable to expect all the intermediate steps to be monotonic
improvements. If anything is to get done, we need to take a little
risk once in a while. Indeed early stage 1 is when we should take
The nice thing is that we have bugzilla to track regressions. We
can fix missed-optimization regressions from now all the way through
stage 3 of 4.3's release cycle. However, I'd expect 4.3 to benchmark
better than 4.2 once Steven is through.
I think everybody by now has understood that the benefit of tree-SSA was
not to replace RTL optimizers, but to make them serve better their
purpose. Removing things such as ADDRESSOF, CONSTANT_P_RTX, QUEUED
allows now to focus on low-level optimizations that cannot be expressed
on the tree level, to understand what needs to be done on the RTL level,
and to do it well.
Everything that will be removed from CSE will most likely not be done on
the tree level (though while developing fwprop we did find one case or
two), but will still happen at the RTL level in a less intertwined and
more easy to maintain way.