https://gcc.gnu.org/g:aa4aafbad5235fd302c39e1d8b7cb9cdea11c67c
commit r16-3802-gaa4aafbad5235fd302c39e1d8b7cb9cdea11c67c
Author: Matteo Nicoli <matteo.nicoli...@gmail.com>
Date: Fri Aug 22 20:42:12 2025 +0200
tree-optimization/121595 - new fabs(a+0.0) -> fabs(a) pattern
With -fno-trapping-math it is safe to optimize fabs(a + 0.0) as
fabs (a).
PR tree-optimization/121595
* match.pd (fabs(a + 0.0) -> fabs (a)): Optimization pattern
limited to
the -fno-trapping-math case.
* gcc.dg/fabs-plus-zero-1.c: New testcase.
* gcc.dg/fabs-plus-zero-2.c: Likewise.
Signed-off-by: Matteo Nicoli <matteo.nicoli...@gmail.com>
Reviewed-by: Andrew Pinski <andrew.pin...@oss.qualcomm.com>
Diff:
---
gcc/match.pd | 9 +++++++++
gcc/testsuite/gcc.dg/fabs-plus-zero-1.c | 9 +++++++++
gcc/testsuite/gcc.dg/fabs-plus-zero-2.c | 10 ++++++++++
3 files changed, 28 insertions(+)
diff --git a/gcc/match.pd b/gcc/match.pd
index b1d7a3a1b73f..f61beb60d270 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -2045,6 +2045,15 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(abs (negate @0))
(abs @0))
+/* fabs(x + 0.0) -> fabs(x), safe even with signed zeros when
-fno-trapping-math.
+ With non-default exception handling denormal + 0.0 might trap.
+ Otherwise !HONOR_SNANS would be sufficient here. */
+(for op (plus minus)
+ (simplify
+ (abs (op @0 real_zerop@1))
+ (if (!flag_trapping_math)
+ (abs @0))))
+
(simplify
(absu (negate @0))
(absu @0))
diff --git a/gcc/testsuite/gcc.dg/fabs-plus-zero-1.c
b/gcc/testsuite/gcc.dg/fabs-plus-zero-1.c
new file mode 100644
index 000000000000..c4a5a298334e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fabs-plus-zero-1.c
@@ -0,0 +1,9 @@
+/* With trapping-math enabled (default behavior), GCC must preserve the +0.0 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+double f(double a)
+{
+ return __builtin_fabs(a + 0.0);
+}
+/* { dg-final { scan-tree-dump-times "\\+ 0\\.0" 1 "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/fabs-plus-zero-2.c
b/gcc/testsuite/gcc.dg/fabs-plus-zero-2.c
new file mode 100644
index 000000000000..0bc7934353d0
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/fabs-plus-zero-2.c
@@ -0,0 +1,10 @@
+/* With -fno-trapping-math it is safe to fold away (+/-)0.0 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-trapping-math -fdump-tree-optimized" } */
+
+double f1(double a) { return __builtin_fabs(a + 0.0); }
+double f2(double a) { return __builtin_fabs(a + -0.0); }
+double f3(double a) { return __builtin_fabs(a - 0.0); }
+double f4(double a) { return __builtin_fabs(a - -0.0); }
+
+/* { dg-final { scan-tree-dump-not "\\+ 0\\.0" "optimized" } } */
