Re: [PATCH] match.pd: Fix x * 0.0 -> 0.0 folding [PR104389]

[Richard Biener via Gcc-patches]

> Am 05.02.2022 um 00:08 schrieb Jakub Jelinek via Gcc-patches 
> <gcc-patches@gcc.gnu.org>:
> 
> Hi!
> 
> The recent PR95115 change to punt in const_binop on folding operation
> with non-NaN operands into NaN if flag_trapping_math broke the following
> testcase, because the x * 0.0 simplification punts just if
> x maybe a NaN (because NaN * 0.0 is NaN not 0.0) or if one of the operands
> could be negative zero.  But Inf * 0.0 or -Inf * 0.0 is also NaN, not
> 0.0, so when NaNs are honored we need to punt for possible infinities too.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk
> and 11/10 where the PR95115 change has been unfortunately backported to
> as well?

Ok


> 2022-02-04  Jakub Jelinek  <ja...@redhat.com>
> 
>    PR tree-optimization/104389
>    (x * 0 -> 0): Punt if x maybe infinite and NaNs are honored.
> 
>    * gcc.dg/pr104389.c: New test.
> 
> --- gcc/match.pd.jj    2022-02-04 14:36:55.393599880 +0100
> +++ gcc/match.pd    2022-02-04 20:30:48.548213594 +0100
> @@ -256,10 +256,12 @@ (define_operator_list SYNC_FETCH_AND_AND
> /* Maybe fold x * 0 to 0.  The expressions aren't the same
>    when x is NaN, since x * 0 is also NaN.  Nor are they the
>    same in modes with signed zeros, since multiplying a
> -   negative value by 0 gives -0, not +0.  */
> +   negative value by 0 gives -0, not +0.  Nor when x is +-Inf,
> +   since x * 0 is NaN.  */
> (simplify
>  (mult @0 real_zerop@1)
>  (if (!tree_expr_maybe_nan_p (@0)
> +      && (!HONOR_NANS (type) || !tree_expr_maybe_infinite_p (@0))
>       && !tree_expr_maybe_real_minus_zero_p (@0)
>       && !tree_expr_maybe_real_minus_zero_p (@1))
>   @1))
> --- gcc/testsuite/gcc.dg/pr104389.c.jj    2022-02-04 20:37:40.579537142 +0100
> +++ gcc/testsuite/gcc.dg/pr104389.c    2022-02-04 20:37:20.787809803 +0100
> @@ -0,0 +1,26 @@
> +/* PR tree-optimization/104389 */
> +/* { dg-do run } */
> +/* { dg-options "-O2" } */
> +/* { dg-add-options ieee } */
> +/* { dg-require-effective-target inf } */
> +
> +__attribute__((noipa)) double
> +foo (void)
> +{
> +  double a = __builtin_huge_val ();
> +  return a * 0.0;
> +}
> +
> +__attribute__((noipa)) long double
> +bar (void)
> +{
> +  return __builtin_huge_vall () * 0.0L;
> +}
> +
> +int
> +main ()
> +{
> +  if (!__builtin_isnan (foo ()) || !__builtin_isnanl (bar ()))
> +    __builtin_abort ();
> +  return 0;
> +}
> 
>    Jakub
>