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From: "wilco at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/106323] [Suboptimal] memcmp(s1, s2, n) == 0 expansion on AArch64 compare to llvm
Date: Mon, 18 Jul 2022 07:31:07 +0000 [thread overview]
Message-ID: <bug-106323-4-UipXNSHUFo@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-106323-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106323
Wilco <wilco at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |wilco at gcc dot gnu.org
--- Comment #3 from Wilco <wilco at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #1)
> GCC might be better if the first bytes are in cache but the next bytes are
> not and then branch is predictable (which it might be).
>
> So this is much more complex than just changing this really.
Neither sequence is efficient. Caches are not really relevant here, it's more
about giving a wide OoO core lots of useful parallel work to do, so avoiding
unnecessary instructions and branches that just slow you down. Hence 4 loads
and CMP+CCMP is best.
next prev parent reply other threads:[~2022-07-18 7:31 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-16 9:55 [Bug c/106323] New: " zhongyunde at huawei dot com
2022-07-17 20:23 ` [Bug middle-end/106323] " pinskia at gcc dot gnu.org
2022-07-17 20:37 ` pinskia at gcc dot gnu.org
2022-07-18 7:31 ` wilco at gcc dot gnu.org [this message]
2022-12-06 13:03 ` zhongyunde at huawei dot com
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