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From: "amonakov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/97832] AoSoA complex caxpy-like loops:
 AVX2+FMA -Ofast 7 times slower than -O3
Date: Fri, 25 Nov 2022 21:27:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97832

Alexander Monakov <amonakov at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amonakov at gcc dot gnu.org

--- Comment #18 from Alexander Monakov <amonakov at gcc dot gnu.org> ---
The apparent 'bias' is introduced by instruction scheduling: haifa-sched li=
fts
a +64 increment over memory accesses, transforming +0 and +32 displacements=
 to
-64 and -32. Sometimes this helps a little bit even on modern x86 CPUs.

Also note that 'vfnmadd231pd 32(%rdx,%rax), %ymm3, %ymm0' would be
'unlaminated' (turned to 2 uops before renaming), so selecting independent =
IVs
for the two arrays actually helps on this testcase.=