x86_64: Add expm1 with FMA

On Skylake, it improves expm1 bench performance by:

        Before       After     Improvement
max     70.204       68.054       3%
min     20.709       16.2         22%
mean    22.1221      16.7367      24%

NB: Add

extern long double __expm1l (long double);
extern long double __expm1f128 (long double);

for __typeof (__expm1l) and __typeof (__expm1f128) when __expm1 is
defined since __expm1 may be expanded in their declarations which
causes the build failure.
---
 sysdeps/ieee754/dbl-64/s_expm1.c           |  7 +++++
 sysdeps/x86_64/fpu/multiarch/Makefile      |  2 ++
 sysdeps/x86_64/fpu/multiarch/s_expm1-fma.c | 10 ++++++
 sysdeps/x86_64/fpu/multiarch/s_expm1.c     | 36 ++++++++++++++++++++++
 4 files changed, 55 insertions(+)
 create mode 100644 sysdeps/x86_64/fpu/multiarch/s_expm1-fma.c
 create mode 100644 sysdeps/x86_64/fpu/multiarch/s_expm1.c

On Fri, Aug 11, 2023 at 8:04 AM H.J. Lu via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> On Skylake, it improves expm1 bench performance by:
>
>         Before       After     Improvement
> max     70.204       68.054       3%
> min     20.709       16.2         22%
> mean    22.1221      16.7367      24%
>
> NB: Add
>
> extern long double __expm1l (long double);
> extern long double __expm1f128 (long double);
>
> for __typeof (__expm1l) and __typeof (__expm1f128) when __expm1 is
> defined since __expm1 may be expanded in their declarations which
> causes the build failure.
> ---
>  sysdeps/ieee754/dbl-64/s_expm1.c           |  7 +++++
>  sysdeps/x86_64/fpu/multiarch/Makefile      |  2 ++
>  sysdeps/x86_64/fpu/multiarch/s_expm1-fma.c | 10 ++++++
>  sysdeps/x86_64/fpu/multiarch/s_expm1.c     | 36 ++++++++++++++++++++++
>  4 files changed, 55 insertions(+)
>  create mode 100644 sysdeps/x86_64/fpu/multiarch/s_expm1-fma.c
>  create mode 100644 sysdeps/x86_64/fpu/multiarch/s_expm1.c
>
> diff --git a/sysdeps/ieee754/dbl-64/s_expm1.c b/sysdeps/ieee754/dbl-64/s_expm1.c
> index 8f1c95bd04..1cafeca9c0 100644
> --- a/sysdeps/ieee754/dbl-64/s_expm1.c
> +++ b/sysdeps/ieee754/dbl-64/s_expm1.c
> @@ -130,6 +130,11 @@ static const double
>           4.00821782732936239552e-06, /* 3ED0CFCA 86E65239 */
>           -2.01099218183624371326e-07 }; /* BE8AFDB7 6E09C32D */
>
> +#ifndef SECTION
> +# define SECTION
> +#endif
> +
> +SECTION
>  double
>  __expm1 (double x)
>  {
> @@ -258,4 +263,6 @@ __expm1 (double x)
>      }
>    return y;
>  }
> +#ifndef __expm1
>  libm_alias_double (__expm1, expm1)
> +#endif
> diff --git a/sysdeps/x86_64/fpu/multiarch/Makefile b/sysdeps/x86_64/fpu/multiarch/Makefile
> index f773255721..add339a876 100644
> --- a/sysdeps/x86_64/fpu/multiarch/Makefile
> +++ b/sysdeps/x86_64/fpu/multiarch/Makefile
> @@ -37,6 +37,7 @@ libm-sysdep_routines += \
>    e_log2-fma \
>    e_pow-fma \
>    s_atan-fma \
> +  s_expm1-fma \
>    s_sin-fma \
>    s_sincos-fma \
>    s_tan-fma \
> @@ -49,6 +50,7 @@ CFLAGS-e_log-fma.c = -mfma -mavx2
>  CFLAGS-e_log2-fma.c = -mfma -mavx2
>  CFLAGS-e_pow-fma.c = -mfma -mavx2
>  CFLAGS-s_atan-fma.c = -mfma -mavx2
> +CFLAGS-s_expm1-fma.c = -mfma -mavx2
>  CFLAGS-s_sin-fma.c = -mfma -mavx2
>  CFLAGS-s_tan-fma.c = -mfma -mavx2
>  CFLAGS-s_sincos-fma.c = -mfma -mavx2
> diff --git a/sysdeps/x86_64/fpu/multiarch/s_expm1-fma.c b/sysdeps/x86_64/fpu/multiarch/s_expm1-fma.c
> new file mode 100644
> index 0000000000..3ee2bd804e
> --- /dev/null
> +++ b/sysdeps/x86_64/fpu/multiarch/s_expm1-fma.c
> @@ -0,0 +1,10 @@
> +#define __expm1 __expm1_fma
> +
> +/* NB: __expm1 may be expanded to __expm1_fma in the following
> +   prototypes.  */
> +extern long double __expm1l (long double);
> +extern long double __expm1f128 (long double);
> +
> +#define SECTION __attribute__ ((section (".text.fma")))
> +
> +#include <sysdeps/ieee754/dbl-64/s_expm1.c>
> diff --git a/sysdeps/x86_64/fpu/multiarch/s_expm1.c b/sysdeps/x86_64/fpu/multiarch/s_expm1.c
> new file mode 100644
> index 0000000000..2cae83fb7f
> --- /dev/null
> +++ b/sysdeps/x86_64/fpu/multiarch/s_expm1.c
> @@ -0,0 +1,36 @@
> +/* Multiple versions of expm1.
> +   Copyright (C) 2023 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/>.  */
> +
> +#include <libm-alias-double.h>
> +
> +extern double __redirect_expm1 (double);
> +
> +#define SYMBOL_NAME expm1
> +#include "ifunc-fma.h"
> +
> +libc_ifunc_redirected (__redirect_expm1, __expm1, IFUNC_SELECTOR ());
> +libm_alias_double (__expm1, expm1)
> +
> +#define __expm1 __expm1_sse2
> +
> +/* NB: __expm1 may be expanded to __expm1_sse2 in the following
> +   prototypes.  */
> +extern long double __expm1l (long double);
> +extern long double __expm1f128 (long double);
> +
> +#include <sysdeps/ieee754/dbl-64/s_expm1.c>
> --
> 2.41.0
>

LGTM.

Hi H.J.,

> On Skylake, it improves expm1 bench performance by:
> 
>         Before       After     Improvement
> max     70.204       68.054       3%
> min     20.709       16.2         22%
> mean    22.1221      16.7367      24%

and it improves slightly the accuracy. The previous largest known error was
0.914 ulp (x=0x1.62f69d171fa65p-2), it is now 0.911:

expm1 0 -1 0x1.63be411e096ep-2 [1] [0.911] 0.910655 0.9106541427171914

LGTM

Paul