From: Roger Sayle <roger@nextmovesoftware.com>
Date: Thu, 25 Nov 2021 19:02:06 +0000 (+0000)
Subject: PR middle-end/103406: Check for Inf before simplifying x-x.
X-Git-Tag: basepoints/gcc-13~2784
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=6ea5fb3cc7f3cc9b731d72183c66c23543876f5a;p=thirdparty%2Fgcc.git

PR middle-end/103406: Check for Inf before simplifying x-x.

This is a simple one line fix to the regression PR middle-end/103406,
where x - x is being folded to 0.0 even when x is +Inf or -Inf.
In GCC 11 and previously, we'd check whether the type honored NaNs
(which implicitly covered the case where the type honors infinities),
but my patch to test whether the operand could potentially be NaN
failed to also check whether the operand could potentially be Inf.

2021-11-25  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	PR middle-end/103406
	* match.pd (minus @0 @0): Check tree_expr_maybe_infinite_p.

gcc/testsuite/ChangeLog
	PR middle-end/103406
	* gcc.dg/pr103406.c: New test case.
---

diff --git a/gcc/match.pd b/gcc/match.pd
index 39fd77ddc4a1..fbb5a5a1eeb9 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -233,7 +233,9 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
    is volatile.  */
 (simplify
  (minus @0 @0)
- (if (!FLOAT_TYPE_P (type) || !tree_expr_maybe_nan_p (@0))
+ (if (!FLOAT_TYPE_P (type)
+      || (!tree_expr_maybe_nan_p (@0)
+	  && !tree_expr_maybe_infinite_p (@0)))
   { build_zero_cst (type); }))
 (simplify
  (pointer_diff @@0 @0)
diff --git a/gcc/testsuite/gcc.dg/pr103406.c b/gcc/testsuite/gcc.dg/pr103406.c
new file mode 100644
index 000000000000..9c7b83b2e9ea
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr103406.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+#define HUGE __DBL_MAX__
+#define INF (HUGE + HUGE)
+#define NAN (INF - INF)
+
+double foo() {
+  double x = -NAN;
+  double y = NAN;
+  return x + y;
+}
+
+/* { dg-final { scan-tree-dump-not "return 0\.0" "optimized" } } */