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From: "linkw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/115355] [12/13/14/15 Regression] vectorization exposes
 wrong code on P9 LE starting from r12-4496
Date: Fri, 07 Jun 2024 08:14:53 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115355

--- Comment #11 from Kewen Lin <linkw at gcc dot gnu.org> ---
(In reply to Jens Seifert from comment #10)
> Does this affect loop vectorize and slp vectorize ?
>=20
> -fno-tree-loop-vectorize avoids loop vectorization to be performed and
> workarounds this issue. Does the same problems also affect SLP
> vectorization, which does not take place in this sample.
>=20
> In other words, do I need
> -fno-tree-loop-vectorize
> or
> -fno-tree-vectorize
> to workaround this bug ?

Since it's an issue on vector merge insn patterns in target code and
vectorization just exposes it, it's hard to workaround this bug completely =
just
by disabling both loop and slp vectorization, as its related bug PR106069
shows, even without vectorization but using some vec merge built-ins, it's
still possible to hit this issue.  But I'd expect disabling both loop and s=
lp
vectorization (-fno-tree-vectorize) can greatly reduce the possibility of
encountering it.=