Re: [PATCH] Skip constant folding for fmin/max when either argument is sNaN [PR105414]

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

On Thu, May 5, 2022 at 10:07 AM HAO CHEN GUI via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi,
>    This patch skips constant folding for fmin/max when either argument
> is sNaN. According to C standard,
>    fmin(sNaN, sNaN）= qNaN, fmin(sNaN, NaN) = qNaN
>    So signaling NaN should be tested and skipped for fmin/max in match.pd.
>
>    Bootstrapped and tested on ppc64 Linux BE and LE with no regressions.
> Is this okay for trunk? Any recommendations? Thanks a lot.

OK.

Thanks,
Richard.

> ChangeLog
>
> 2022-05-05 Haochen Gui <guihaoc@linux.ibm.com>
>
> gcc/
>         PR target/105414
>         * match.pd (minmax): Skip constant folding for fmin/fmax when both
>         arguments are sNaN or one is sNaN and another is NaN.
>
> gcc/testsuite/
>         PR target/105414
>         * gcc.dg/pr105414.c: New.
>
> patch.diff
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index cad61848daa..f256bcbb483 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -3093,7 +3093,9 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>  (for minmax (min max FMIN_ALL FMAX_ALL)
>   (simplify
>    (minmax @0 @0)
> -  @0))
> +  /* if both are sNaN, it should return qNaN.  */
> +  (if (!tree_expr_maybe_signaling_nan_p (@0))
> +    @0)))
>  /* min(max(x,y),y) -> y.  */
>  (simplify
>   (min:c (max:c @0 @1) @1)
> @@ -3193,12 +3195,13 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>     (minmax @1 (convert @2)))))
>
>  (for minmax (FMIN_ALL FMAX_ALL)
> - /* If either argument is NaN, return the other one.  Avoid the
> -    transformation if we get (and honor) a signalling NaN.  */
> + /* If either argument is NaN and other one is not sNaN, return the other
> +    one.  Avoid the transformation if we get (and honor) a signalling NaN.  */
>   (simplify
>    (minmax:c @0 REAL_CST@1)
> -  (if (real_isnan (TREE_REAL_CST_PTR (@1))
> -       && (!HONOR_SNANS (@1) || !TREE_REAL_CST (@1).signalling))
> +   (if (real_isnan (TREE_REAL_CST_PTR (@1))
> +       && (!HONOR_SNANS (@1) || !TREE_REAL_CST (@1).signalling)
> +       && !tree_expr_maybe_signaling_nan_p (@0))
>     @0)))
>  /* Convert fmin/fmax to MIN_EXPR/MAX_EXPR.  C99 requires these
>     functions to return the numeric arg if the other one is NaN.
> diff --git a/gcc/testsuite/gcc.dg/pr105414.c b/gcc/testsuite/gcc.dg/pr105414.c
> new file mode 100644
> index 00000000000..78772700acf
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr105414.c
> @@ -0,0 +1,30 @@
> +/* { dg-do run { target { *-*-linux* *-*-gnu* } } } */
> +/* { dg-options "-O1 -fsignaling-nans -lm" } */
> +/* { dg-add-options ieee } */
> +/* { dg-require-effective-target issignaling } */
> +
> +
> +#define _GNU_SOURCE
> +#include <stdio.h>
> +#include <math.h>
> +
> +int main()
> +{
> +  double a = __builtin_nans ("");
> +
> +  if (issignaling (fmin (a, a)))
> +    __builtin_abort ();
> +
> +  if (issignaling (fmax (a, a)))
> +    __builtin_abort ();
> +
> +  double b = __builtin_nan ("");
> +
> +  if (issignaling (fmin (a, b)))
> +    __builtin_abort ();
> +
> +  if (issignaling (fmax (a, b)))
> +    __builtin_abort ();
> +
> +  return 0;
> +}