x86_64: Add tanh with FMA

On Skylake, it improves tanh bench performance by:

	Before 		After 		Improvement
max	110.89		95.826		14%
min	20.966		20.157		4%
mean	30.9601		29.8431		4%

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

sysdeps/ieee754/dbl-64/s_tanh.c

@@ -46,6 +46,11 @@ static char rcsid[] = "$NetBSD: s_tanh.c,v 1.7 1995/05/10 20:48:22 jtc Exp $";
 
 static const double one = 1.0, two = 2.0, tiny = 1.0e-300;
 
+#ifndef SECTION
+# define SECTION
+#endif
+
+SECTION
 double
 __tanh (double x)
 {

sysdeps/x86_64/fpu/multiarch/Makefile

@@ -10,6 +10,7 @@ CFLAGS-s_expm1-fma.c = -mfma -mavx2
 CFLAGS-s_log1p-fma.c = -mfma -mavx2
 CFLAGS-s_sin-fma.c = -mfma -mavx2
 CFLAGS-s_tan-fma.c = -mfma -mavx2
+CFLAGS-s_tanh-fma.c = -mfma -mavx2
 CFLAGS-s_sincos-fma.c = -mfma -mavx2
 CFLAGS-s_exp10m1f-fma.c = -mfma -mavx2
 CFLAGS-s_exp2m1f-fma.c = -mfma -mavx2
@@ -96,6 +97,7 @@ libm-sysdep_routines += \
   s_sinf-sse2 \
   s_tan-avx \
   s_tan-fma \
+  s_tanh-fma \
   s_trunc-sse4_1 \
   s_truncf-sse4_1 \
 # libm-sysdep_routines

sysdeps/x86_64/fpu/multiarch/s_tanh-fma.c

@@ -0,0 +1,11 @@
+#define __tanh __tanh_fma
+#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_tanh.c>

sysdeps/x86_64/fpu/multiarch/s_tanh.c

@@ -0,0 +1,31 @@
+/* Multiple versions of tanh.
+   Copyright (C) 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/>.  */
+
+#include <sysdeps/x86/isa-level.h>
+#if MINIMUM_X86_ISA_LEVEL < AVX2_X86_ISA_LEVEL
+
+extern double __redirect_tanh (double);
+
+# define SYMBOL_NAME tanh
+# include "ifunc-fma.h"
+
+libc_ifunc_redirected (__redirect_tanh, __tanh, IFUNC_SELECTOR ());
+
+# define __tanh __tanh_sse2
+#endif
+#include <sysdeps/ieee754/dbl-64/s_tanh.c>