match.pd: Optimize a * !a to 0 [PR114009]

match.pd: Optimize a * !a to 0 [PR114009]

The following patch attempts to fix an optimization regression through
adding a simple simplification.  We already have the
/* (m1 CMP m2) * d -> (m1 CMP m2) ? d : 0  */
(if (!canonicalize_math_p ())
 (for cmp (tcc_comparison)
  (simplify
   (mult:c (convert (cmp@0 @1 @2)) @3)
   (if (INTEGRAL_TYPE_P (type)
        && INTEGRAL_TYPE_P (TREE_TYPE (@0)))
     (cond @0 @3 { build_zero_cst (type); })))
optimization which otherwise triggers during the a * !a multiplication,
but that is done only late and we aren't able through range assumptions
optimize it yet anyway.

The patch adds a specific simplification for it.
If a is zero, then a * !a will be 0 * 1 (or for signed 1-bit 0 * -1)
and so 0.
If a is non-zero, then a * !a will be a * 0 and so again 0.
THe pattern is valid for scalar integers, complex integers and vector types,
but I think will actually trigger only for the scalar integers.  For
vector types I've added other two with VEC_COND_EXPR in it, for complex
there are different GENERIC trees to match and it is something that likely
would be never matched in GIMPLE, so I didn't handle that.

2024-03-07  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/114009
	* genmatch.cc (decision_tree::gen): Emit ARG_UNUSED for captures
	argument even for GENERIC, not just for GIMPLE.
	* match.pd (a * !a -> 0): New simplifications.

	* gcc.dg/tree-ssa/pr114009.c: New test.