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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/115749] Non optimal assembly for integer modulo by a constant on x86-64 CPUs
Date: Tue, 02 Jul 2024 18:14:28 +0000 [thread overview]
Message-ID: <bug-115749-4-5GIm9jnJQh@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-115749-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115749
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2024-07-02
Depends on| |115756
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #5)
> For the original testcase, the imul vs shift can be reduced down to just:
> ```
> unsigned long func(unsigned long x)
> {
> return x * 240;
> }
>
> ```
>
> GCC produces:
> ```
> movq %rdi, %rax
> salq $4, %rax
> subq %rdi, %rax
> salq $4, %rax
> ```
> vs:
> ```
> imulq $240, %rdi, %rax
> ```
>
> -mtune=skylake produces the imul.
I split out the tuning issue for imul to PR 115756 .
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115756
[Bug 115756] default tuning for x86_64 produces shifts for `*240`
next prev parent reply other threads:[~2024-07-02 18:14 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-07-02 9:31 [Bug c++/115749] New: Missed BMI2 optimization on x86-64 kim.walisch at gmail dot com
2024-07-02 11:36 ` [Bug c++/115749] " kim.walisch at gmail dot com
2024-07-02 11:44 ` [Bug target/115749] Non optimal assembly for integer modulo by a constant on x86-64 CPUs pinskia at gcc dot gnu.org
2024-07-02 11:59 ` kim.walisch at gmail dot com
2024-07-02 12:17 ` kim.walisch at gmail dot com
2024-07-02 17:21 ` pinskia at gcc dot gnu.org
2024-07-02 17:58 ` pinskia at gcc dot gnu.org
2024-07-02 18:14 ` pinskia at gcc dot gnu.org [this message]
2024-07-02 18:41 ` pinskia at gcc dot gnu.org
2024-07-03 17:29 ` kim.walisch at gmail dot com
2024-07-04 1:17 ` liuhongt at gcc dot gnu.org
2024-07-16 8:18 ` lingling.kong7 at gmail dot com
2024-07-16 21:29 ` roger at nextmovesoftware dot com
2024-07-25 1:45 ` cvs-commit at gcc dot gnu.org
2024-08-15 5:11 ` liuhongt at gcc dot gnu.org
2024-08-15 5:35 ` liuhongt at gcc dot gnu.org
2024-08-16 5:00 ` sjames at gcc dot gnu.org
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