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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/102473] [12 Regression] 521.wrf_r 5% slower at -Ofast
 and generic x86_64 tuning after r12-3426-g8f323c712ea76c
Date: Fri, 24 Sep 2021 07:50:11 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102473

Richard Biener <rguenth at gcc dot gnu.org> changed:

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

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Hongtao.liu from comment #2)
> (In reply to Richard Biener from comment #1)
> > Looks like at least on Zen movs[hl]dup is on the integer domain so we'l=
 see
> > a domain crossing penalty here(?).  But since this is a generic arch/tu=
ning
> > regression the SSE2 code path should be what matters - on the committed
> > testcase I see
> >=20
> > foo:
> > .LFB572:
> >         .cfi_startproc
> >         pxor    %xmm0, %xmm0
> >         addss   (%rdi), %xmm0
> >         addss   4(%rdi), %xmm0
> >         addss   8(%rdi), %xmm0
> >         addss   12(%rdi), %xmm0
> >         ret
> >=20
> > where it seems that the vectorizer doesn't pick up the reduction patter=
n.
> >=20
> Guess you're use O3, -ffast-math is needed for v4sf reduction
> https://godbolt.org/z/sjf4Pncna

I was looking at the testcase as compiled by the testsuite.

It seems that adding __attribute__((optimize("tree-vectorize"))) makes the
loop no longer vectorized as it at the moment cancels -ffast-math.

IIRC when Martin commits his optimize() re-org it will no longer do that.=