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[Bug rtl-optimization/57193] [4.9/5/6 Regression] suboptimal register allocation for SSE registers
- From: "bernds at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 14 Jan 2016 16:39:23 +0000
- Subject: [Bug rtl-optimization/57193] [4.9/5/6 Regression] suboptimal register allocation for SSE registers
- Auto-submitted: auto-generated
- References: <bug-57193-4 at http dot gcc dot gnu dot org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57193
Bernd Schmidt <bernds at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |bernds at gcc dot gnu.org
--- Comment #9 from Bernd Schmidt <bernds at gcc dot gnu.org> ---
It looks like the situation is as follows (X is the LRA-created reload reg)
X = a
op on X
b = X
where a and b are different registers already allocated by IRA, hence we can
avoid one copy at most. I'm not very familiar with LRA yet, but I see no code
to rethink such register allocation choices.
-frename-registers gets rid of one unnecessary copy, it was enhanced to detect
such situations for gcc-6. Maybe we should finally enable that for -O2 and
higher?