Re: [GCC][PATCH][mid-end] Optimize x * copysign (1.0, y) [Patch (1/2)]

[Tamar Christina <Tamar dot Christina at arm dot com>]

Hi Andrew,

Thanks! I'll put together the rest today or tomorrow.
Sorry for the slow response on this one.

Tamar
________________________________________
From: Andrew Pinski <pinskia@gmail.com>
Sent: Monday, June 26, 2017 3:09:54 AM
To: Tamar Christina
Cc: GCC Patches; nd; law@redhat.com; ian@airs.com; rguenther@suse.de
Subject: Re: [GCC][PATCH][mid-end] Optimize x * copysign (1.0, y) [Patch (1/2)]

On Sat, Jun 24, 2017 at 4:53 PM, Andrew Pinski <pinskia@gmail.com> wrote:
> On Mon, Jun 12, 2017 at 12:56 AM, Tamar Christina
> <Tamar.Christina@arm.com> wrote:
>> Hi All,
>>
>> this patch implements a optimization rewriting
>>
>> x * copysign (1.0, y) and
>> x * copysign (-1.0, y)
>
>
> This reminds me:
> copysign(-1.0, y) can be just optimized to:
> copysign(1.0, y)
>
> I did that in my patch here:
> https://gcc.gnu.org/ml/gcc-patches/2017-06/msg01860.html

I updated the patch to handle all constants and not just -1.0.

>
> This should allow you to reduce the number of patterns needed to match here.
> Note I still think we could do this in expand without a new
> builtin/internal function.
> I might go and code that up soonish.

Also something like attached (NOTE this is NOT a full patch and needs
the xorsign optabs part of your patch) should work for the expand side
rather than creating a new builtin.  There still needs to handling of
the vector based copysign.  But you should get the general idea.  I
would like to see more of these special expand patterns really.

NOTE you can remove the target hook part and just check if xorsign
optab is there.  I don't know if that is what we want to do if not
allow for generic expanding of this.

Thanks,
Andrew Pinski


>
> Thanks,
> Andrew
>
>>
>> to:
>>
>> x ^ (y & (1 << sign_bit_position))
>>
>> This is done by creating a special builtin during matching and generate the
>> appropriate instructions during expand. This new builtin is called XORSIGN.
>>
>> The expansion of xorsign depends on if the backend has an appropriate optab
>> available. If this is not the case then we use a modified version of the existing
>> copysign which does not take the abs value of the first argument as a fall back.
>>
>> This patch is a revival of a previous patch
>> https://gcc.gnu.org/ml/gcc-patches/2015-10/msg00069.html
>>
>> Bootstrapped on both aarch64-none-linux-gnu and x86_64 with no issues.
>> Regression done on aarch64-none-linux-gnu and no regressions.
>>
>> Ok for trunk?
>>
>> gcc/
>> 2017-06-07  Tamar Christina  <tamar.christina@arm.com>
>>
>>         * builtins.def (BUILT_IN_XORSIGN, BUILT_IN_XORSIGNF): New.
>>         (BUILT_IN_XORSIGNL, BUILT_IN_XORSIGN_FLOAT_NX): Likewise.
>>         * match.pd (mult (COPYSIGN:s real_onep @0) @1): New simplifier.
>>         (mult (COPYSIGN:s real_mus_onep @0) @1): Likewise.
>>         (copysigns @0 (negate @1)): Likewise.
>>         * builtins.c (expand_builtin_copysign): Promoted local to argument.
>>         (expand_builtin): Added CASE_FLT_FN_FLOATN_NX (BUILT_IN_XORSIGN) and
>>         CASE_FLT_FN (BUILT_IN_XORSIGN).
>>         (BUILT_IN_COPYSIGN): Updated function call.
>>         * optabs.h (expand_copysign): New bool.
>>         (expand_xorsign): New.
>>         * optabs.def (xorsign_optab): New.
>>         * optabs.c (expand_copysign): New parameter.
>>         * fortran/f95-lang.c (xorsignl, xorsign, xorsignf): New.
>>         * fortran/mathbuiltins.def (XORSIGN): New.
>>
>> gcc/testsuite/
>> 2017-06-07  Tamar Christina  <tamar.christina@arm.com>
>>
>>         * gcc.dg/tree-ssa/xorsign.c: New.
>>         * gcc.dg/xorsign_exec.c: New.
>>         * gcc.dg/vec-xorsign_exec.c: New.
>>         * gcc.dg/tree-ssa/reassoc-39.c (f2, f3): Updated constant to 2.