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

On Mon, Aug 10, 2026 at 6:50 AM Dipesh Sharma <[email protected]> wrote:
>
> 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 ?

Ok.

>
>
> 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
>