[PATCH 15/15] x86_64: Add asinpif with FMA

[Adhemerval Zanella Netto]

On 10/02/25 22:31, DJ Delorie wrote:
> 
> LGTM
> 
> Reviewed-by: DJ Delorie <dj@redhat.com>
> 
> Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:
>> The CORE-MATH asinpif implementation showed slight worse performance
>> when using x86_64 baseline ABI due its usage of fma on fast path.
>> This patch adds a ifunc variant with similar performance for x86_64-v3.
> 
> Do you have the performance numbers to report?

It turns out that Paul has suggested to just remove the fma operation [1]
on the fast-path; which makes the code faster on x86_64 and x86_64-v2
and the iFUNC variant not required anymore.  I will update the asinpif
with the new performance numbers. 

[1] https://gitlab.inria.fr/core-math/core-math/-/commit/ccdd955b6fa614c8d88bd1d6fd323abaf43cfb3f

> 
>> ---
>>  sysdeps/ieee754/flt-32/s_asinpif.c           |  2 ++
>>  sysdeps/x86_64/fpu/multiarch/Makefile        |  2 ++
>>  sysdeps/x86_64/fpu/multiarch/s_asinpif-fma.c |  4 +++
>>  sysdeps/x86_64/fpu/multiarch/s_asinpif.c     | 33 ++++++++++++++++++++
> 
> So this is an ifunc of asinpf() itself, not fma...
> 
>> diff --git a/sysdeps/ieee754/flt-32/s_asinpif.c b/sysdeps/ieee754/flt-32/s_asinpif.c
>>        return r;
>>      }
>>  }
>> +#ifndef __asinpif
>>  libm_alias_float (__asinpi, asinpi)
>> +#endif
> 
> Ok.
> 
>> diff --git a/sysdeps/x86_64/fpu/multiarch/Makefile b/sysdeps/x86_64/fpu/multiarch/Makefile
>>  CFLAGS-s_sincos-fma.c = -mfma -mavx2
>>  CFLAGS-s_exp10m1f-fma.c = -mfma -mavx2
>>  CFLAGS-s_exp2m1f-fma.c = -mfma -mavx2
>> +CFLAGS-s_asinpif-fma.c = -mfma -mavx2
>>  
>>  CFLAGS-e_exp2f-fma.c = -mfma -mavx2
>>  CFLAGS-e_expf-fma.c = -mfma -mavx2
>> @@ -68,6 +69,7 @@ libm-sysdep_routines += \
>>    e_logf-fma \
>>    e_pow-fma \
>>    e_powf-fma \
>> +  s_asinpif-fma \
>>    s_atan-avx \
>>    s_atan-fma \
>>    s_ceil-sse4_1 \
> 
> Ok.
> 
>> diff --git a/sysdeps/x86_64/fpu/multiarch/s_asinpif-fma.c b/sysdeps/x86_64/fpu/multiarch/s_asinpif-fma.c
>> +#define __asinpif __asinpif_fma
>> +#define SECTION __attribute__ ((section (".text.fma")))
>> +
>> +#include <sysdeps/ieee754/flt-32/s_asinpif.c>
> 
> So same code, but without the alias and built with different options, to
> make a variant.  Ok.
> 
>> diff --git a/sysdeps/x86_64/fpu/multiarch/s_asinpif.c b/sysdeps/x86_64/fpu/multiarch/s_asinpif.c
>> +/* Multiple versions of asinpif.
>> +   Copyright (C) 2024-2025 Free Software Foundation, Inc.
>> +   This file is part of the GNU C Library.
>> +
>> +   The GNU C Library is free software; you can redistribute it and/or
>> +   modify it under the terms of the GNU Lesser General Public
>> +   License as published by the Free Software Foundation; either
>> +   version 2.1 of the License, or (at your option) any later version.
>> +
>> +   The GNU C Library is distributed in the hope that it will be useful,
>> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> +   Lesser General Public License for more details.
>> +
>> +   You should have received a copy of the GNU Lesser General Public
>> +   License along with the GNU C Library; if not, see
>> +   <https://www.gnu.org/licenses/>.  */
> 
> Ok.
> 
>> +#include <sysdeps/x86/isa-level.h>
>> +#if MINIMUM_X86_ISA_LEVEL < AVX2_X86_ISA_LEVEL
>> +# include <libm-alias-float.h>
>> +
>> +extern float __redirect_asinpif (float);
>> +
>> +# define SYMBOL_NAME asinpif
>> +# include "ifunc-fma.h"
>> +
>> +libc_ifunc_redirected (__redirect_asinpif, __asinpif, IFUNC_SELECTOR ());
>> +libm_alias_float (__asinpi, asinpi)
>> +
>> +# define __asinpif __asinpif_sse2
>> +#endif
>> +#include <sysdeps/ieee754/flt-32/s_asinpif.c>
> 
> So if the build picks this *.c file, it adds the ifunc code but also
> includes the default asinpf() as __asinpif_sse2().  Ok.
>