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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/109154] [13 regression] jump threading
 de-optimizes nested floating point comparisons
Date: Thu, 13 Apr 2023 17:29:26 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109154

--- Comment #47 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The testcase then doesn't have to be floating point, say on x86 -O3 -mavx51=
2f
void
foo (int *f, int d, int e)
{
  for (int i =3D 0; i < 1024; i++)
    {
      int a =3D f[i];
      int t;
      if (a < 0)
        t =3D 1;
      else if (a < e)
        t =3D 1 - a * d;
      else
        t =3D 0;
      f[i] =3D t;
    }
}
shows similar problems.  Strangely, for
void
foo (int *f, int d, int e)
{
  if (e < 32 || e > 64)
    __builtin_unreachable ();
  for (int i =3D 0; i < 1024; i++)
    {
      int a =3D f[i];
      f[i] =3D (a < 0 ? 1 : 1 - a * d) * (a < e ? 1 : 0);
    }
}
the threader doesn't do what it does for floating point code and we use jus=
t 2
comparisons rather than 3 (or more).  Still, only one multiplication, not 2.
Strangely, in that case the second multiplication is there until vrp2, which
folds it using
/* Transform x * { 0 or 1, 0 or 1, ... } into x & { 0 or -1, 0 or -1, ...},
   unless the target has native support for the former but not the latter. =
 */
match.pd pattern and others into oblivion.=