[PATCH] PR tree-optimization/126693: Fold abs(x) * abs(y) -> abs(x * y).

Hi all,

This patch addresses the issue https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126693.

The optimization is not valid for the following cases:

- fp with -frounding-math.
- Integers with wrapping arithmetic and signed integer overflow.
- values to be folded must have single use otherwise we may end up adding an extra ABS_EXPR.

e.g.
int gx, gy, mul;
void f (int x, int y)
{
  int ax = __builtin_abs (x);
  int ay = __builtin_abs (y);
  mul = ax * ay;
  gx = ax; // use of ax
  gy = ay; // use of ay
}

regtested and bootstraped on x86_64-linux-gnu. ok for trunk ?


gcc/ChangeLog:
	PR tree-optimization/126693.
	* match.pd: Fold abs(x) * abs(y) into abs(x * y).

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/mult-abs-3.c: New test.
	* gcc.dg/tree-ssa/mult-abs-4.c: New test.
	* gcc.dg/tree-ssa/mult-abs-5.c: New test.
---
 gcc/match.pd                               | 10 +++++++
 gcc/testsuite/gcc.dg/tree-ssa/mult-abs-3.c | 17 ++++++++++++
 gcc/testsuite/gcc.dg/tree-ssa/mult-abs-4.c | 32 ++++++++++++++++++++++
 gcc/testsuite/gcc.dg/tree-ssa/mult-abs-5.c |  7 +++++
 4 files changed, 66 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/mult-abs-3.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/mult-abs-4.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/mult-abs-5.c

diff --git a/gcc/match.pd b/gcc/match.pd
index a2a48e1b475..379fa98a692 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -1254,6 +1254,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
  (mult (absu@1 @0) @1)
  (mult (convert@2 @0) @2))
 
+/* abs(x) * abs(y) -> abs(x * y).  */
+(simplify
+ (mult (abs:s @0) (abs:s @1))
+ (if ((FLOAT_TYPE_P (type)
+       && !HONOR_SIGN_DEPENDENT_ROUNDING (type))
+      || (ANY_INTEGRAL_TYPE_P (type)
+	  && TYPE_OVERFLOW_UNDEFINED (type)
+	  && !TYPE_OVERFLOW_SANITIZED (type)))
+  (abs (mult @0 @1))))
+
 #if GIMPLE
 /* Simplify SAD(x, x, acc) -> acc since the absolute difference is zero.  */
 (simplify
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/mult-abs-3.c b/gcc/testsuite/gcc.dg/tree-ssa/mult-abs-3.c
new file mode 100644
index 00000000000..2bebafc65b0
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/mult-abs-3.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target c99_runtime } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+#include <stdlib.h>
+
+double    f (double x, double y)          { return __builtin_fabs  (x) * __builtin_fabs  (y); }
+float     g (float x, float y)            { return __builtin_fabsf (x) * __builtin_fabsf (y); }
+int       h (int x, int y)                { return __builtin_abs   (x) * __builtin_abs   (y); }
+long      i (long x, long y)              { return __builtin_labs  (x) * __builtin_labs  (y); }
+long long j (long long x, long long y)    { return __builtin_llabs (x) * __builtin_llabs (y); }
+
+int       k (int x, int y)                { return abs   (x) * abs   (y); }
+long      l (long x, long y)              { return labs  (x) * labs  (y); }
+long long m (long long x, long long y)    { return llabs (x) * llabs (y); }
+
+/* { dg-final { scan-tree-dump-times "ABS_EXPR" 8 "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/mult-abs-4.c b/gcc/testsuite/gcc.dg/tree-ssa/mult-abs-4.c
new file mode 100644
index 00000000000..4979dfd5207
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/mult-abs-4.c
@@ -0,0 +1,32 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+double __attribute__((optimize ("-frounding-math")))
+frnd (double x, double y)
+{
+  return __builtin_fabs (x) * __builtin_fabs (y);
+}
+
+int __attribute__((optimize ("-fwrapv")))
+wrap (int x, int y)
+{
+  return __builtin_abs (x) * __builtin_abs (y);
+}
+
+int __attribute__((optimize ("-ftrapv")))
+trap (int x, int y)
+{
+  return __builtin_abs (x) * __builtin_abs (y);
+}
+
+int gx, gy;
+int shared (int x, int y)
+{
+  int ax = __builtin_abs (x);
+  int ay = __builtin_abs (y);
+  gx = ax;
+  gy = ay;
+  return ax * ay;
+}
+
+/* { dg-final { scan-tree-dump-times "ABS_EXPR" 8 "optimized" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/mult-abs-5.c b/gcc/testsuite/gcc.dg/tree-ssa/mult-abs-5.c
new file mode 100644
index 00000000000..860b931c376
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/mult-abs-5.c
@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fsanitize=signed-integer-overflow -fdump-tree-optimized" } */
+
+int  f (int x, int y)   { return __builtin_abs  (x) * __builtin_abs  (y); }
+long g (long x, long y) { return __builtin_labs (x) * __builtin_labs (y); }
+
+/* { dg-final { scan-tree-dump-times "ABS_EXPR" 4 "optimized" } } */
-- 
2.34.1