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


On Wed, Jun 28, 2017 at 10:50 AM, Christophe Lyon
<christophe.lyon@linaro.org> wrote:
> On 25 June 2017 at 23:28, Andrew Pinski <pinskia@gmail.com> wrote:
>> On Sun, Jun 25, 2017 at 11:18 AM, Andrew Pinski <pinskia@gmail.com> wrote:
>>> On Sun, Jun 25, 2017 at 1:28 AM, Marc Glisse <marc.glisse@inria.fr> 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))))))
>>>>
>>>> There is already a 1.0 of the right type in the input, it would be easier to
>>>> reuse it in the output than build a new one.
>>>
>>> Right.  Fixed.
>>>
>>>>
>>>> Non-generic builtins like copysign are such a pain... We also end up missing
>>>> the 128-bit case that way (pre-existing problem, not your patch). We seem to
>>>> have a corresponding internal function, but apparently it is not used until
>>>> expansion (well, maybe during vectorization).
>>>
>>> Yes I noticed that while working on a different patch related to
>>> copysign; The generic version of a*copysign(1.0, b) [see the other
>>> thread where the ARM folks started a patch for it; yes it was by pure
>>> accident that I was working on this and really did not notice that
>>> thread until yesterday].
>>> I was looking into a nice way of creating copysign without having to
>>> do the switch but I could not find one.  In the end I copied was done
>>> already in a different location in match.pd; this is also the reason
>>> why I had the build_one_cst there.
>>>
>>>>
>>>> + /* 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_minus_onep real_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); } (outn @0)))
>>>> +    (if (types_match (type, double_type_node))
>>>> +     (BUILT_IN_COPYSIGN { build_one_cst (type); } (outn @0)))
>>>> +    (if (types_match (type, long_double_type_node))
>>>> +     (BUILT_IN_COPYSIGNL { build_one_cst (type); } (outn @0)))))))
>>>> +
>>>> +/* Transform X * copysign (1.0, X) into abs(X). */
>>>> +(simplify
>>>> + (mult:c @0 (COPYSIGN real_onep @0))
>>>> + (if (!HONOR_NANS (type) && !HONOR_SIGNED_ZEROS (type))
>>>> +  (abs @0)))
>>>>
>>>> I would have expected it do to the right thing for signed zero and qNaN. Can
>>>> you describe a case where it would give the wrong result, or are the
>>>> conditions just conservative?
>>>
>>> I was just being conservative; maybe too conservative but I was a bit
>>> worried I could get it incorrect.
>>>
>>>>
>>>> +/* Transform X * copysign (1.0, -X) into -abs(X). */
>>>> +(simplify
>>>> + (mult:c @0 (COPYSIGN real_onep (negate @0)))
>>>> + (if (!HONOR_NANS (type) && !HONOR_SIGNED_ZEROS (type))
>>>> +  (negate (abs @0))))
>>>> +
>>>> +/* Transform copysign (-1.0, X) into copysign (1.0, X). */
>>>> +(simplify
>>>> + (COPYSIGN real_minus_onep @0)
>>>> + (COPYSIGN { build_one_cst (type); } @0))
>>>>
>>>> (simplify
>>>>  (COPYSIGN REAL_CST@0 @1)
>>>>  (if (REAL_VALUE_NEGATIVE (TREE_REAL_CST (@0)))
>>>>   (COPYSIGN (negate @0) @1)))
>>>> ? Or does that create trouble with sNaN and only the 1.0 case is worth
>>>> the trouble?
>>>
>>> No that is the correct way; I Noticed the other thread about copysign
>>> had something similar as what should be done too.
>>>
>>> I will send out a new patch after testing soon.
>>
>> New patch.
>> OK? Bootstrapped and tested on aarch64-linux-gnu with no regressions.
>>
> Hi Andrew,
>
> 2 of the new testcases fail on aarch64*-elf:
> FAIL:    gcc.dg/tree-ssa/copy-sign-1.c scan-tree-dump-times gimple "copysign" 8
> FAIL:    gcc.dg/tree-ssa/mult-abs-2.c scan-tree-dump-times gimple "ABS" 8
>
> The attached patch makes them unsupported by requiring c99_runtime
> effective-target.
>
> OK?

Ok.

>
>> Thanks,
>> Andrew Pinski
>>
>> ChangeLog:
>> * match.pd (X >/>=/</<= 0 ? 1.0 : -1.0): New patterns.
>> (X * copysign (1.0, X)): New pattern.
>> (X * copysign (1.0, -X)): New pattern.
>> (copysign (-1.0, CST)): New pattern.
>>
>> testsuite/ChangeLog:
>> * gcc.dg/tree-ssa/copy-sign-1.c: New testcase.
>> * gcc.dg/tree-ssa/copy-sign-2.c: New testcase.
>> * gcc.dg/tree-ssa/mult-abs-2.c: New testcase.
>>
>>>
>>> Thanks,
>>> Andrew
>>>
>>>>
>>>> --
>>>> Marc Glisse


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