[PATCH v2 4/5] powerpc: Remove modf optimization

[Sachin Monga]

Looks fine again.

Reviewed-by: Sachin Monga <smonga@linux.ibm.com>


Regards:
Sachin.

On 16/06/25 6:47 pm, Adhemerval Zanella wrote:
> The generic implementation is slight more optimized than the powerpc
> one, where it has a more optimized inf/nan check (by not using FP
> unit checks, along with branch prediction hints), and removed one
> branch by issuing trunc instead of a combination of floor/ceil (which
> also generated less code).
>
> On power10 with gcc 14.2.1:
>
> reciprocal-throughput        master         patch        difference
> workload-0_1                 1.1351        0.9067            20.12%
> workload-1_maxint            1.4230        0.9040            36.47%
> workload-maxint_maxfloat     1.5038        0.9076            39.65%
> workload-integral            1.1280        0.9111            19.23%
>
> latency                      master         patch        difference
> workload-0_1                 1.1440        2.7117          -137.03%
> workload-1_maxint            4.0556        2.7070            33.25%
> workload-maxint_maxfloat     3.2122        2.7164            15.43%
> workload-integral            3.2381        2.7281            15.75%
>
> Checked on powerpc64le-linux-gnu.
> ---
>   sysdeps/powerpc/fpu/math-use-builtins-trunc.h |  3 +-
>   sysdeps/powerpc/fpu/s_modf.c                  | 59 -------------------
>   .../power4/fpu/multiarch/s_modf-power5+.c     |  2 +-
>   .../be/fpu/multiarch/s_modf-power5+.c         |  2 +-
>   4 files changed, 4 insertions(+), 62 deletions(-)
>   delete mode 100644 sysdeps/powerpc/fpu/s_modf.c
>
> diff --git a/sysdeps/powerpc/fpu/math-use-builtins-trunc.h b/sysdeps/powerpc/fpu/math-use-builtins-trunc.h
> index fd186d3510..3e6a55d2ca 100644
> --- a/sysdeps/powerpc/fpu/math-use-builtins-trunc.h
> +++ b/sysdeps/powerpc/fpu/math-use-builtins-trunc.h
> @@ -1,8 +1,9 @@
> -#define USE_TRUNC_BUILTIN 0
>   #ifdef _ARCH_PWR5X
>   # define USE_TRUNCF_BUILTIN 1
> +# define USE_TRUNC_BUILTIN 1
>   #else
>   # define USE_TRUNCF_BUILTIN 0
> +# define USE_TRUNC_BUILTIN 0
>   #endif
>   #define USE_TRUNCL_BUILTIN 0
>   #define USE_TRUNCF128_BUILTIN 0
> diff --git a/sysdeps/powerpc/fpu/s_modf.c b/sysdeps/powerpc/fpu/s_modf.c
> deleted file mode 100644
> index 831072bdc3..0000000000
> --- a/sysdeps/powerpc/fpu/s_modf.c
> +++ /dev/null
> @@ -1,59 +0,0 @@
> -/* Copyright (C) 2013-2025 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 Library General Public License as
> -   published by the Free Software Foundation; either version 2 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
> -   Library General Public License for more details.
> -
> -   You should have received a copy of the GNU Library General Public
> -   License along with the GNU C Library; see the file COPYING.LIB.  If
> -   not, see <https://www.gnu.org/licenses/>.  */
> -
> -/* ISA 2.07 provides fast GPR to FP instruction (mfvsr{d,wz}) which make
> -   generic implementation faster.  Also disables for old ISAs that do not
> -   have ceil/floor instructions.  */
> -#if defined(_ARCH_PWR8) || !defined(_ARCH_PWR5X)
> -# include <sysdeps/ieee754/ldbl-opt/s_modf.c>
> -#else
> -# include <math.h>
> -# include <math_ldbl_opt.h>
> -# include <libm-alias-double.h>
> -
> -double
> -__modf (double x, double *iptr)
> -{
> -  if (__builtin_isinf (x))
> -    {
> -      *iptr = x;
> -      return copysign (0.0, x);
> -    }
> -  else if (__builtin_isnan (x))
> -    {
> -      *iptr = NAN;
> -      return NAN;
> -    }
> -
> -  if (x >= 0.0)
> -    {
> -      *iptr = floor (x);
> -      return copysign (x - *iptr, x);
> -    }
> -  else
> -    {
> -      *iptr = ceil (x);
> -      return copysign (x - *iptr, x);
> -    }
> -}
> -# ifndef __modf
> -libm_alias_double (__modf, modf)
> -#  if LONG_DOUBLE_COMPAT (libc, GLIBC_2_0)
> -compat_symbol (libc, __modf, modfl, GLIBC_2_0);
> -#  endif
> -# endif
> -#endif
> diff --git a/sysdeps/powerpc/powerpc32/power4/fpu/multiarch/s_modf-power5+.c b/sysdeps/powerpc/powerpc32/power4/fpu/multiarch/s_modf-power5+.c
> index b8315c5b81..48f3a1997d 100644
> --- a/sysdeps/powerpc/powerpc32/power4/fpu/multiarch/s_modf-power5+.c
> +++ b/sysdeps/powerpc/powerpc32/power4/fpu/multiarch/s_modf-power5+.c
> @@ -17,4 +17,4 @@
>      <https://www.gnu.org/licenses/>.  */
>   
>   #define __modf __modf_power5plus
> -#include <sysdeps/powerpc/fpu/s_modf.c>
> +#include <sysdeps/ieee754/dbl-64/s_modf.c>
> diff --git a/sysdeps/powerpc/powerpc64/be/fpu/multiarch/s_modf-power5+.c b/sysdeps/powerpc/powerpc64/be/fpu/multiarch/s_modf-power5+.c
> index b8315c5b81..48f3a1997d 100644
> --- a/sysdeps/powerpc/powerpc64/be/fpu/multiarch/s_modf-power5+.c
> +++ b/sysdeps/powerpc/powerpc64/be/fpu/multiarch/s_modf-power5+.c
> @@ -17,4 +17,4 @@
>      <https://www.gnu.org/licenses/>.  */
>   
>   #define __modf __modf_power5plus
> -#include <sysdeps/powerpc/fpu/s_modf.c>
> +#include <sysdeps/ieee754/dbl-64/s_modf.c>