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From: "moncef.mechri at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/110551] [11/12/13/14 Regression] an extra mov when doing 128bit multiply
Date: Tue, 04 Jul 2023 18:12:17 +0000	[thread overview]
Message-ID: <bug-110551-4-HPdwWHdQY0@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-110551-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110551

--- Comment #3 from Moncef Mechri <moncef.mechri at gmail dot com> ---
> Please next time attach (which you can do paste in the box) or paste inline
> the testcase rather than just link to godbolt .

Noted. Apologies.

> It is an older regression though.
> ```
> #include <stdint.h>
> 
> void mulx64(uint64_t *x, uint64_t *t)
> {
>     __uint128_t r = (__uint128_t)*x * 0x9E3779B97F4A7C15ull;
>     *t = (uint64_t)r ^ (uint64_t)( r >> 64 );
> }
> ```
> 
> It is just an extra mov.
> 
> Also the mulx should have allowed the register allocator to do better but it
> was worse ...

It is true that with this new test case, all GCC versions (including GCC 10)
seem to suffer from both issues reported in the original post.

But the original test case only exhibits suboptimal codegen for GCC >= 11, as
shown in the godbolt link shared above.

  parent reply	other threads:[~2023-07-04 18:12 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-04 17:26 [Bug rtl-optimization/110551] New: [11 / 12 / 13 /14 regression] Suboptimal codegen for 128 bits multiplication on x86_64 moncef.mechri at gmail dot com
2023-07-04 17:32 ` [Bug target/110551] [11/12/13/14 " pinskia at gcc dot gnu.org
2023-07-04 17:47 ` [Bug target/110551] [11/12/13/14 Regression] an extra mov when doing 128bit multiply pinskia at gcc dot gnu.org
2023-07-04 18:12 ` moncef.mechri at gmail dot com [this message]
2023-07-05  7:06 ` rguenth at gcc dot gnu.org
2023-10-18 19:11 ` roger at nextmovesoftware dot com
2023-10-27  9:05 ` cvs-commit at gcc dot gnu.org
2023-10-29 18:01 ` moncef.mechri at gmail dot com
2023-11-01 10:06 ` ubizjak at gmail dot com
2023-11-01 22:35 ` cvs-commit at gcc dot gnu.org
2023-11-06 19:24 ` moncef.mechri at gmail dot com
2023-11-12 15:48 ` [Bug target/110551] [11/12/13 " roger at nextmovesoftware dot com

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