From bb5e895245ebef488b63efc239f64488aef65cf1 Mon Sep 17 00:00:00 2001
From: Jakub Jelinek <jakub@redhat.com>
Date: Tue, 25 Aug 2020 07:21:26 +0200
Subject: [PATCH] match.pd: Simplify copysign (x, -x) to -x [PR96715]

The following patch implements an optimization suggested in the PR,
copysign(x,-x) can be optimized into -x (even without -ffast-math,
should work fine even for signed zeros and infinities or nans).

2020-08-25  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/96715
	* match.pd (copysign(x,-x) -> -x): New simplification.

	* gcc.dg/tree-ssa/copy-sign-3.c: New test.
---
 gcc/match.pd                                |  5 +++++
 gcc/testsuite/gcc.dg/tree-ssa/copy-sign-3.c | 23 +++++++++++++++++++++++
 2 files changed, 28 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/copy-sign-3.c

diff --git a/gcc/match.pd b/gcc/match.pd
index 2cffcae..6e45836 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -5294,6 +5294,11 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
  @0)
 
 (simplify
+ /* copysign(x,-x) -> -x.  */
+ (COPYSIGN_ALL @0 (negate@1 @0))
+ @1)
+
+(simplify
  /* copysign(x,y) -> fabs(x) if y is nonnegative.  */
  (COPYSIGN_ALL @0 tree_expr_nonnegative_p@1)
  (abs @0))
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/copy-sign-3.c b/gcc/testsuite/gcc.dg/tree-ssa/copy-sign-3.c
new file mode 100644
index 0000000..f52e04d2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/copy-sign-3.c
@@ -0,0 +1,23 @@
+/* PR tree-optimization/96715 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-final { scan-tree-dump-not "= __builtin_copysign" "optimized" } } */
+/* { dg-final { scan-tree-dump-times " = -x_\[0-9]*\\(D\\)" 3 "optimized" } } */
+
+float
+foo (float x)
+{
+  return __builtin_copysignf (x, -x);
+}
+
+double
+bar (double x)
+{
+  return __builtin_copysign (x, -x);
+}
+
+long double
+baz (long double x)
+{
+  return __builtin_copysignl (x, -x);
+}
-- 
2.7.4