powerpc: Remove modf optimization

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

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

sysdeps/powerpc/fpu/s_modf.c

@@ -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

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>

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>