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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/113982] Poor codegen for 64-bit add with carry widening functions
Date: Sun, 18 Feb 2024 19:42:31 +0000	[thread overview]
Message-ID: <bug-113982-4-AaWFcCdCIp@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-113982-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113982

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

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

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
We pattern recognize just something like (or r < y):
add_result add_wide_3(unsigned long long x, unsigned long long y) {
    auto r = x + y;
    return add_result{r, r < x};
}
and not doing the addition uselessly in twice as big mode + shift + comparison
against 0.
The reason for mov edx, 0 is not to clobber flags which are live at that point,
of course one could also move the clearing of edx one insn earlier and then it
could be xor edx, edx.

  parent reply	other threads:[~2024-02-18 19:42 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-02-18 19:07 [Bug c++/113982] New: " janschultke at googlemail dot com
2024-02-18 19:20 ` [Bug middle-end/113982] " pinskia at gcc dot gnu.org
2024-02-18 19:23 ` pinskia at gcc dot gnu.org
2024-02-18 19:42 ` jakub at gcc dot gnu.org [this message]
2024-02-19  8:16 ` rguenth at gcc dot gnu.org
2024-02-19  8:22 ` jakub at gcc dot gnu.org
2024-05-10 13:02 ` jakub at gcc dot gnu.org
2024-05-10 16:27 ` jakub at gcc dot gnu.org
2024-05-13  9:17 ` cvs-commit at gcc dot gnu.org
2024-05-13  9:25 ` jakub at gcc dot gnu.org

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