match.pd: Fix x * 0.0 -> 0.0 folding [PR104389]

The recent PR95115 change to punt in const_binop on folding operation
with non-NaN operands into NaN if flag_trapping_math broke the following
testcase, because the x * 0.0 simplification punts just if
x maybe a NaN (because NaN * 0.0 is NaN not 0.0) or if one of the operands
could be negative zero.  But Inf * 0.0 or -Inf * 0.0 is also NaN, not
0.0, so when NaNs are honored we need to punt for possible infinities too.

2022-02-05  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/104389
	* match.pd (x * 0 -> 0): Punt if x maybe infinite and NaNs are
	honored.

	* gcc.dg/pr104389.c: New test.

diff --git a/gcc/match.pd b/gcc/match.pd
index 10ff867e8543df7509af93fbe059eca609a23d2b..7bbb80172fc786af220ed9f6cd124a0b1f7f44ae 100644 (file)
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -256,10 +256,12 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 /* Maybe fold x * 0 to 0.  The expressions aren't the same
    when x is NaN, since x * 0 is also NaN.  Nor are they the
    same in modes with signed zeros, since multiplying a
-   negative value by 0 gives -0, not +0.  */
+   negative value by 0 gives -0, not +0.  Nor when x is +-Inf,
+   since x * 0 is NaN.  */
 (simplify
  (mult @0 real_zerop@1)
  (if (!tree_expr_maybe_nan_p (@0)
+      && (!HONOR_NANS (type) || !tree_expr_maybe_infinite_p (@0))
       && !tree_expr_maybe_real_minus_zero_p (@0)
       && !tree_expr_maybe_real_minus_zero_p (@1))
   @1))

diff --git a/gcc/testsuite/gcc.dg/pr104389.c b/gcc/testsuite/gcc.dg/pr104389.c
new file mode 100644 (file)
index 0000000..0c6c85a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr104389.c
@@ -0,0 +1,26 @@
+/* PR tree-optimization/104389 */
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+/* { dg-add-options ieee } */
+/* { dg-require-effective-target inf } */
+
+__attribute__((noipa)) double
+foo (void)
+{
+  double a = __builtin_huge_val ();
+  return a * 0.0;
+}
+
+__attribute__((noipa)) long double
+bar (void)
+{
+  return __builtin_huge_vall () * 0.0L;
+}
+
+int
+main ()
+{
+  if (!__builtin_isnan (foo ()) || !__builtin_isnanl (bar ()))
+    __builtin_abort ();
+  return 0;
+}