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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/101186] predictable comparison of integer
 variables not folded
Date: Thu, 24 Jun 2021 06:49:54 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101186

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |85316

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
The complication is that the a =3D=3D b equivalence has to be taken into ac=
count to
relate the c < a and c >=3D b relations.

Maybe the new relation code can do sth here, but confirmed on trunk.

void g (int a, int b, int x, int y)
{
  int c =3D y;
  if (a !=3D 0)
    c =3D x;
  while (b < 1000)
  // without this loop, jump thread & VRP can remove dead code
    {
      if (a !=3D 0)
        {
          if (c > x)
            printf ("Unreachable!");
        }

that's also a classical example for predicated value-numbering (which we
don't implement).


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D85316
[Bug 85316] [meta-bug] VRP range propagation missed cases=