match.pd: Optimize __builtin_mul_overflow_p (x, cst, (utype)0) to x > ~(utype)0 ...

A comparison with a constant is most likely always faster than
.MUL_OVERFLOW from which we only check whether it overflowed and not the
multiplication result, and even if not, it is simpler operation on GIMPLE
and even if a target exists where such multiplications with overflow checking
are cheaper than comparisons, because comparisons are so much more common
than overflow checking multiplications, it would be nice if it simply
arranged for comparisons to be emitted like those multiplications on its
own...

2022-06-01  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/30314
	* match.pd (__builtin_mul_overflow_p (x, cst, (utype) 0) ->
	x > ~(utype)0 / cst): New simplification.

	* gcc.dg/tree-ssa/pr30314.c: New test.

diff --git a/gcc/match.pd b/gcc/match.pd
index 88c6c414881dd02b8d61302bfa730fc48138d081..2d3ffc4482e767311f99700386f6ed233ba15762 100644 (file)
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -5969,6 +5969,17 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
        && (!TYPE_UNSIGNED (TREE_TYPE (@2)) || TYPE_UNSIGNED (TREE_TYPE (@0))))
    (ovf @1 @0))))
 
+/* Optimize __builtin_mul_overflow_p (x, cst, (utype) 0) if all 3 types
+   are unsigned to x > (umax / cst).  */
+(simplify
+ (imagpart (IFN_MUL_OVERFLOW:cs@2 @0 integer_nonzerop@1))
+  (if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
+       && TYPE_UNSIGNED (TREE_TYPE (@0))
+       && TYPE_MAX_VALUE (TREE_TYPE (@0))
+       && types_match (TREE_TYPE (@0), TREE_TYPE (TREE_TYPE (@2)))
+       && int_fits_type_p (@1, TREE_TYPE (@0)))
+   (convert (gt @0 (trunc_div! { TYPE_MAX_VALUE (TREE_TYPE (@0)); } @1)))))
+
 /* Simplification of math builtins.  These rules must all be optimizations
    as well as IL simplifications.  If there is a possibility that the new
    form could be a pessimization, the rule should go in the canonicalization

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr30314.c b/gcc/testsuite/gcc.dg/tree-ssa/pr30314.c
new file mode 100644 (file)
index 0000000..91388af
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr30314.c
@@ -0,0 +1,18 @@
+/* PR middle-end/30314 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-final { scan-tree-dump-not "\.MUL_OVERFLOW " "optimized" } } */
+/* { dg-final { scan-tree-dump " > 122713351" "optimized" { target int32 } } } */
+/* { dg-final { scan-tree-dump " > 527049830677415760" "optimized" { target lp64 } } } */
+
+int
+foo (unsigned int x)
+{
+  return __builtin_mul_overflow_p (x, 35U, 0U);
+}
+
+int
+bar (unsigned long int x)
+{
+  return __builtin_mul_overflow_p (x, 35UL, 0UL);
+}