RE: [PATCH] Fold (a > 0 ? 1.0 : -1.0) into copysign (1.0, a) and a * copysign (1.0, a) into abs(a)

[Richard Biener <richard dot guenther at gmail dot com>]

On June 27, 2017 4:52:28 PM GMT+02:00, Tamar Christina <Tamar.Christina@arm.com> wrote:
>> >> +(for cmp (gt ge lt le)
>> >> +     outp (convert convert negate negate)
>> >> +     outn (negate negate convert convert)
>> >> + /* Transform (X > 0.0 ? 1.0 : -1.0) into copysign(1, X). */
>> >> + /* Transform (X >= 0.0 ? 1.0 : -1.0) into copysign(1, X). */
>> >> + /* Transform (X < 0.0 ? 1.0 : -1.0) into copysign(1,-X). */
>> >> + /* Transform (X <= 0.0 ? 1.0 : -1.0) into copysign(1,-X). */
>> >> +(simplify
>> >> +  (cond (cmp @0 real_zerop) real_onep real_minus_onep)
>> >> +  (if (!HONOR_NANS (type) && !HONOR_SIGNED_ZEROS (type)
>> >> +       && types_match (type, TREE_TYPE (@0)))
>> >> +   (switch
>> >> +    (if (types_match (type, float_type_node))
>> >> +     (BUILT_IN_COPYSIGNF { build_one_cst (type); } (outp @0)))
>> >> +    (if (types_match (type, double_type_node))
>> >> +     (BUILT_IN_COPYSIGN { build_one_cst (type); } (outp @0)))
>> >> +    (if (types_match (type, long_double_type_node))
>> >> +     (BUILT_IN_COPYSIGNL { build_one_cst (type); } (outp @0))))))
>> >>
>
>Hi,
>
>Out of curiosity is there any reason why this transformation can't be
>more general?
>
>e.g. Transform (X > 0.0 ? CST : -CST) into copysign(CST, X).

That's also possible, yes.

>we would at the very least avoid a csel or a branch then.
>
>Regards,
>Tamar