[Bug target/93006] Better code with a-- == 0 rather than --a == -1

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93006

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=96702
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2023-09-05

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed, the problem is the single_use usage in:
/* For equality, this is also true with wrapping overflow.  */
(for op (eq ne)
 (simplify
  (op:c (nop_convert?@3 (plus:c@2 @0 (convert1? @1))) (convert2? @1))
  (if (ANY_INTEGRAL_TYPE_P (TREE_TYPE (@0))
       && (TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@0))
           || TYPE_OVERFLOW_WRAPS (TREE_TYPE (@0)))
       && (CONSTANT_CLASS_P (@0) || (single_use (@2) && single_use (@3)))
       && tree_nop_conversion_p (TREE_TYPE (@3), TREE_TYPE (@2))
       && tree_nop_conversion_p (TREE_TYPE (@3), TREE_TYPE (@1)))
   (op @0 { build_zero_cst (TREE_TYPE (@0)); })))


Similar as for the minus case, see PR 96702 for that ...