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From: "lis8215 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/111384] New: missed optimization: GCC adds extra any
 extend when storing subreg#0 multiple times
Date: Tue, 12 Sep 2023 09:25:21 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111384

            Bug ID: 111384
           Summary: missed optimization: GCC adds extra any extend when
                    storing subreg#0 multiple times
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lis8215 at gmail dot com
  Target Milestone: ---

Simple example:

void store_hi_twice(uint32_t src, uint16_t *dst1, uint16_t *dst2)
{
    *dst1 =3D src;
    *dst2 =3D src;
}

shows that GCC can't opt out unnecessary zero extend of the src's low half
aimed to store two or more times. Many targets are affected, although x86-64
don't.=