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

@@ -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

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

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>

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>