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

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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.
This commit is contained in:
Jakub Jelinek 2024-03-07 08:43:16 +01:00
parent 1cd8254eba
commit 95b6ee9634
3 changed files with 45 additions and 1 deletions
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2
gcc/genmatch.cc
View file

@ -4071,7 +4071,7 @@ decision_tree::gen (vec <FILE *> &files, bool gimple)
for (unsigned i = 0;
i < as_a <expr *>(s->s->s->match)->ops.length (); ++i)
fp_decl (f, " tree ARG_UNUSED (_p%d),", i);
fp_decl (f, " tree *captures");
fp_decl (f, " tree *ARG_UNUSED (captures)");
}
for (unsigned i = 0; i < s->s->s->for_subst_vec.length (); ++i)
{

11
gcc/match.pd
View file

@ -1219,6 +1219,17 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
&& tree_nop_conversion_p (type, TREE_TYPE (@1)))
(lshift @0 @2)))
/* Fold a * !a into 0. */
(simplify
(mult:c @0 (convert? (eq @0 integer_zerop)))
{ build_zero_cst (type); })
(simplify
(mult:c @0 (vec_cond (eq @0 integer_zerop) @1 integer_zerop))
{ build_zero_cst (type); })
(simplify
(mult:c @0 (vec_cond (ne @0 integer_zerop) integer_zerop @1))
{ build_zero_cst (type); })
/* Shifts by precision or greater result in zero. */
(for shift (lshift rshift)
(simplify

33
gcc/testsuite/gcc.dg/tree-ssa/pr114009.c Normal file
View file

@ -0,0 +1,33 @@
/* PR tree-optimization/114009 */
/* { dg-do compile } */
/* { dg-options "-O2 -Wno-psabi -fdump-tree-forwprop1" } */
/* { dg-final { scan-tree-dump-times " return 0;" 3 "forwprop1" } } */
/* { dg-final { scan-tree-dump-times " (?:return|<retval> =) { 0, 0, 0, 0 };" 1 "forwprop1" } } */
int
foo (int x)
{
x = (x / 2) * 2;
return (!x) * x;
}
int
bar (int x, int y)
{
(void) x;
return y * !y;
}
unsigned long long
baz (unsigned long long x)
{
return (!x) * x;
}
typedef int V __attribute__((vector_size (4 * sizeof (int))));
V
qux (V x)
{
return x * (x == 0);
}