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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/92080] Missed CSE of _mm512_set1_epi8(c) with
 _mm256_set1_epi8(c)
Date: Thu, 21 Mar 2024 08:31:49 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D92080

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
But it's even simpler than the cited case - the mode has the same size (for=
 the
latest testcase, not for the original one, of course).

It's also that after reload a zeroing of V4SImode will also zero ymm but
of course setting V4SImode to all-ones will not set the upper half of
ymm to all-ones but instead "zero-extends".

With CSE it becomes then important what set comes first.  If the larger mode
set comes first it's easier.  If the smaller mode set comes first you'd
have to change that to a larger one (if the zero-extension is not what you
want).=