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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/94793] Failure to optimize clz idiom
Date: Thu, 07 May 2020 17:06:12 +0000	[thread overview]
Message-ID: <bug-94793-4-RS3pGxfd3M@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-94793-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94793

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
You mean like PR82479 ?  Though, __builtin_clz is UB at zero, so it would need
to be v >>= 1; r = v ? 32 - __builtin_clz(v) : 0; v = 0; or so, except that on
aarch64 (or where we CLZ_DEFINED_VALUE_AT_ZERO as 2, i.e. guarantee if CLZ ifn
or builtins to have the behavior defined at GIMPLE rather than say just RTL or
never).  And on other targets that have CLZ_DEFINED_VALUE_AT_ZERO 1 with value
of precision, perhaps convert that conditional into just CLZ at RTL time.

  parent reply	other threads:[~2020-05-07 17:06 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-27 10:00 [Bug tree-optimization/94793] New: " gabravier at gmail dot com
2020-04-27 10:12 ` [Bug tree-optimization/94793] " rguenth at gcc dot gnu.org
2020-05-07 17:06 ` jakub at gcc dot gnu.org [this message]
2021-08-03 23:20 ` pinskia at gcc dot gnu.org
2022-05-25 13:37 ` tnfchris at gcc dot gnu.org
2023-01-16 10:48 ` cvs-commit at gcc dot gnu.org

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