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[Bug rtl-optimization/79593] [6/7 Regression] Poor/Worse code generation for FPU on versions after 6
- From: "ubizjak at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Tue, 21 Feb 2017 19:31:04 +0000
- Subject: [Bug rtl-optimization/79593] [6/7 Regression] Poor/Worse code generation for FPU on versions after 6
- Auto-submitted: auto-generated
- References: <bug-79593-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79593
Uroš Bizjak <ubizjak at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords|missed-optimization |ra
Status|WAITING |NEW
CC| |vmakarov at gcc dot gnu.org
Component|target |rtl-optimization
--- Comment #15 from Uroš Bizjak <ubizjak at gmail dot com> ---
For the remaining issue:
mov eax, DWORD PTR [eax+4]
...
mov DWORD PTR [esp], eax # worse than v6: spills to stack!
fld DWORD PTR [esp] # instead of 'fsubr DWORD PTR [eax+4]'
fsubrp st(2), st
register allocator doesn't figure out that it loaded eax from [eax+4] a couple
of insns above - instead of a spill, it can access the value from the same
location.
This is a RA regression from gcc-5.