Re: [PATCHv2] move the (a-b) CMP 0 ? (a-b) : (b-a) optimization from fold_cond_expr_with_comparison to match

[Richard Biener <richard.guenther@gmail.com>]

On Sun, Oct 22, 2023 at 2:13 AM Andrew Pinski <pinskia@gmail.com> wrote:
>
> From: Andrew Pinski <apinski@marvell.com>
>
> This patch moves the `(a-b) CMP 0 ? (a-b) : (b-a)` optimization
> from fold_cond_expr_with_comparison to match.
>
> Bootstrapped and tested on x86_64-linux-gnu.

OK.

> Changes in:
> v2: Removes `(a == b) ? 0 : (b - a)` handling since it was handled
>     via r14-3606-g3d86e7f4a8ae
>     Change zerop to integer_zerop for `(a - b) == 0 ? 0 : (b - a)`,
>     Add `(a - b) != 0 ? (a - b) : 0` handling.
>
> gcc/ChangeLog:
>
>         * match.pd (`(A - B) CMP 0 ? (A - B) : (B - A)`):
>         New patterns.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.dg/tree-ssa/phi-opt-38.c: New test.
> ---
>  gcc/match.pd                               | 46 ++++++++++++++++++++--
>  gcc/testsuite/gcc.dg/tree-ssa/phi-opt-38.c | 45 +++++++++++++++++++++
>  2 files changed, 88 insertions(+), 3 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/phi-opt-38.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index a56838fb388..ce8d159d260 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -5650,9 +5650,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>    (cnd (logical_inverted_value truth_valued_p@0) @1 @2)
>    (cnd @0 @2 @1)))
>
> -/* abs/negative simplifications moved from fold_cond_expr_with_comparison,
> -   Need to handle (A - B) case as fold_cond_expr_with_comparison does.
> -   Need to handle UN* comparisons.
> +/* abs/negative simplifications moved from fold_cond_expr_with_comparison.
>
>     None of these transformations work for modes with signed
>     zeros.  If A is +/-0, the first two transformations will
> @@ -5717,6 +5715,48 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>         (convert (negate (absu:utype @0))))
>         (negate (abs @0)))))
>   )
> +
> + /* (A - B) == 0 ? (A - B) : (B - A)    same as (B - A) */
> + (for cmp (eq uneq)
> +  (simplify
> +   (cnd (cmp (minus@0 @1 @2) zerop) @0 (minus@3 @2 @1))
> +   (if (!HONOR_SIGNED_ZEROS (type))
> +    @3))
> +  (simplify
> +   (cnd (cmp (minus@0 @1 @2) integer_zerop) integer_zerop (minus@3 @2 @1))
> +   @3)
> + )
> + /* (A - B) != 0 ? (A - B) : (B - A)    same as (A - B) */
> + (for cmp (ne ltgt)
> +  (simplify
> +   (cnd (cmp (minus@0 @1 @2) zerop) @0 (minus @2 @1))
> +   (if (!HONOR_SIGNED_ZEROS (type))
> +    @0))
> +  (simplify
> +   (cnd (cmp (minus@0 @1 @2) integer_zerop) @0 integer_zerop)
> +   @0)
> + )
> + /* (A - B) >=/> 0 ? (A - B) : (B - A)    same as abs (A - B) */
> + (for cmp (ge gt)
> +  (simplify
> +   (cnd (cmp (minus@0 @1 @2) zerop) @0 (minus @2 @1))
> +   (if (!HONOR_SIGNED_ZEROS (type)
> +       && !TYPE_UNSIGNED (type))
> +    (abs @0))))
> + /* (A - B) <=/< 0 ? (A - B) : (B - A)    same as -abs (A - B) */
> + (for cmp (le lt)
> +  (simplify
> +   (cnd (cmp (minus@0 @1 @2) zerop) @0 (minus @2 @1))
> +   (if (!HONOR_SIGNED_ZEROS (type)
> +       && !TYPE_UNSIGNED (type))
> +    (if (ANY_INTEGRAL_TYPE_P (type)
> +        && !TYPE_OVERFLOW_WRAPS (type))
> +     (with {
> +        tree utype = unsigned_type_for (type);
> +      }
> +      (convert (negate (absu:utype @0))))
> +      (negate (abs @0)))))
> + )
>  )
>
>  /* -(type)!A -> (type)A - 1.  */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/phi-opt-38.c b/gcc/testsuite/gcc.dg/tree-ssa/phi-opt-38.c
> new file mode 100644
> index 00000000000..0f0e3170f8d
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/phi-opt-38.c
> @@ -0,0 +1,45 @@
> +/* { dg-options "-O2 -fno-signed-zeros -fdump-tree-phiopt" } */
> +int minus1(int a, int b)
> +{
> +  int c = a - b;
> +  if (c == 0) c = b - a;
> +  return c;
> +}
> +int minus2(int a, int b)
> +{
> +  int c = a - b;
> +  if (c != 0) c = b - a;
> +  return c;
> +}
> +int minus3(int a, int b)
> +{
> +  int c = a - b;
> +  if (c == 0) c = 0;
> +  else c = b - a;
> +  return c;
> +}
> +int minus4(int a, int b)
> +{
> +  int c;
> +  if (a == b) c = 0;
> +  else
> +    c = b - a;
> +  return c;
> +}
> +int abs0(int a, int b)
> +{
> +  int c = a - b;
> +  if (c <= 0) c = b - a;
> +  return c;
> +}
> +int negabs(int a, int b)
> +{
> +  int c = a - b;
> +  if (c >= 0) c = b - a;
> +  return c;
> +}
> +
> +/* The above should be optimized at phiopt1 except for negabs which has to wait
> +  until phiopt2 as -abs is not acceptable in early phiopt.  */
> +/* { dg-final { scan-tree-dump-times "if" 1  "phiopt1"  } } */
> +/* { dg-final { scan-tree-dump-not "if" "phiopt2" } } */
> --
> 2.39.3
>