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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/97307] Optimization for pure vs. const function
Date: Wed, 07 Oct 2020 14:51:46 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97307

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
The patch will cause

FAIL: gcc.dg/vect/pr65947-3.c scan-tree-dump-times vect "LOOP VECTORIZED" 2

since the testcase has exactly such a pattern:

unsigned int
condition_reduction (unsigned int *a, unsigned int min_v, unsigned int *b)
{
  unsigned int last =3D N + 65;
  unsigned int aval;

  for (unsigned int i =3D 0; i < N; i++)
    {
      aval =3D a[i];
      if (b[i] < min_v)
        last =3D aval;
    }
  return last;
}

and sinking the aval =3D a[i] load causes if-conversion to no longer happen
because a[i] now appears to only conditionally trap.  It will be vectorized
with masked loads if those are available though, so I'm considering to
XFAIL it for the moment.=