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From: "crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/111402] New: Loop distribution fail to optimize
 memmove for multiple consecutive moves within a loop
Date: Wed, 13 Sep 2023 09:47:21 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: middle-end
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: missed-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111402

            Bug ID: 111402
           Summary: Loop distribution fail to optimize memmove for
                    multiple consecutive moves within a loop
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: crazylht at gmail dot com
  Target Milestone: ---

cat test.c

typedef long long v4di __attribute__((vector_size(32)));

void
foo (v4di* __restrict a, v4di *b, int n)
{
  for (int i =3D 0; i !=3D n; i++)
    a[i] =3D b[i];
}

void
foo1 (v4di* __restrict a, v4di *b, int n)
{
  for (int i =3D 0; i !=3D n; i+=3D2)
    {
    a[i] =3D b[i];
    a[i+1] =3D b[i+1];=20=20=20
    }
}


gcc -O2 -S test.c

GCC can optimize loop in foo to memmove, but not for loop in foo1.
This is from PR111354=