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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/102951] failure to optimize MIN_EXPR of
 subobject addresses of the same object
Date: Tue, 26 Oct 2021 16:49:51 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102951

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
extern int a[];

int *
foo (void)
{
  int *p1 =3D &a[1];
  int *p2 =3D &a[2];
  return p1 < p2 ? p1 : p2;
}

int
bar (void)
{
  int *p1 =3D &a[1];
  int *p2 =3D &a[2];
  return p1 < p2;
}

For the latter function, we optimize it in match.pd:
/* When the addresses are not directly of decls compare base and offset.
   This implements some remaining parts of fold_comparison address
   comparisons but still no complete part of it.  Still it is good
   enough to make fold_stmt not regress when not dispatching to fold_binary=
.=20
*/
(for cmp (simple_comparison)
 (simplify
  (cmp (convert1?@2 addr@0) (convert2? addr@1))
  (with
   {
     poly_int64 off0, off1;
...

So, I guess for MIN_EXPR/MAX_EXPR with ADDR_EXPR operands, we can optimize =
it
similarly, the question is if we should try to do that through
repeating that huge code from there, or try to outline big parts of that in=
to a
helper function, or perhaps could we e.g. do
  (with
    {
#if GENERIC
      tree l =3D generic_simplify (..., LT_EXPR, ...);
#else
      tree l =3D gimple_simplify (..., LT_EXPR, ...);
#endif
    }
    (if (l && integer_zerop (l))
      @0)
     (if (l && integer_nonzerop (l))
       @1)))
or so?
and therefore try to fold LT_EXPR instead of MIN_EXPR or MAX_EXPR and if th=
at
folds into integer_zerop or integer_nonzerop=