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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/115395] [15 regression] libarchive
 miscompiled with -O2 -march=znver2 -fno-vect-cost-model since
 r15-1006-gd93353e6423eca
Date: Mon, 10 Jun 2024 07:31:51 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115395

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
It needs epilogue vectorization to trigger and it's the path re-using the
vector accumulator from the earlier loop that goes wrong when the main
vector loop is skipped.

We apply the initial value adjustment to the scalar result but the
continuation fails to do this and the epilogue vector epilogue expects
the earlier code to have done it.

IIRC we force "optimization" of this to be disabled but obviously somehow
fail to do this for SLP.=