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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/106365] Miss to handle ifn .LEN_STORE in FRE
Date: Wed, 20 Jul 2022 09:01:52 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106365

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
int __attribute__((noinline,noclone))
foo (int *out)
{
  int mask[] =3D { 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1,
      0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1 };
  int i;
  for (i =3D 0; i < 32; ++i)
    {
      if (mask[i])
        out[i] =3D i;
    }
  return out[7];
}

testcase for x86_64 and .MASK_STORE, could be optimized to return 1.  FRE
sees

  .MASK_STORE (out_41(D), 32B, mask__7.9_47, { 0, 1, 2, 3, 4, 5, 6, 7 });
  _10 =3D &mask[8] + 32;
  MEM <vector(8) int> [(int *)_10] =3D { 0, 1, 0, 1, 0, 1, 0, 1 };

and 'mask' having address taken makes it clobbered by .MASK_STORE.  There's
also the older issue that when mask is incoming but marked __restrict that
isn't good enough because __restrict and calls doesn't work.

The IL with .LEN_STORE might suffer similar issues at the point FRE gets
to see it.

We might be able to improve BB SLP to not code-gen

  _10 =3D &mask[8] + 32;
  MEM <vector(8) int> [(int *)_10] =3D { 0, 1, 0, 1, 0, 1, 0, 1 };

here, making 'mask' addressable again.  I have a patch for this in testing.=