x86_64: Add atanh with FMA

On SPR, it improves atanh bench performance by:

			Before		After		Improvement
reciprocal-throughput	15.1715		14.8628		2%
latency			57.1941		56.1883		2%

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

benchtests/atanh-inputs

@@ -1,6 +1,7 @@
 ## args: double
 ## ret: double
 ## includes: math.h
+## name: workload-random
 0x1.5a2730bacd94ap-1
 -0x1.b57eb40fc048ep-21
 -0x1.c0b185fb450e2p-17

sysdeps/ieee754/dbl-64/e_atanh.c

@@ -44,6 +44,11 @@
 
 static const double huge = 1e300;
 
+#ifndef SECTION
+# define SECTION
+#endif
+
+SECTION
 double
 __ieee754_atanh (double x)
 {
@@ -73,4 +78,7 @@ __ieee754_atanh (double x)
 
   return copysign (t, x);
 }
+
+#ifndef __ieee754_atanh
 libm_alias_finite (__ieee754_atanh, __atanh)
+#endif

sysdeps/x86_64/fpu/multiarch/Makefile

@@ -1,6 +1,7 @@
 ifeq ($(subdir),math)
 CFLAGS-e_asin-fma.c = -mfma -mavx2
 CFLAGS-e_atan2-fma.c = -mfma -mavx2
+CFLAGS-e_atanh-fma.c = -mfma -mavx2
 CFLAGS-e_exp-fma.c = -mfma -mavx2
 CFLAGS-e_log-fma.c = -mfma -mavx2
 CFLAGS-e_log2-fma.c = -mfma -mavx2
@@ -59,6 +60,7 @@ libm-sysdep_routines += \
   e_asin-fma \
   e_atan2-avx \
   e_atan2-fma \
+  e_atanh-fma \
   e_exp-avx \
   e_exp-fma \
   e_exp2f-fma \

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

@@ -0,0 +1,6 @@
+#define __ieee754_atanh __ieee754_atanh_fma
+#define __log1p __log1p_fma
+
+#define SECTION __attribute__ ((section (".text.fma")))
+
+#include <sysdeps/ieee754/dbl-64/e_atanh.c>

sysdeps/x86_64/fpu/multiarch/e_atanh.c

@@ -0,0 +1,34 @@
+/* Multiple versions of atanh.
+   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
+# include <libm-alias-finite.h>
+
+extern double __redirect_ieee754_atanh (double);
+
+# define SYMBOL_NAME ieee754_atanh
+# include "ifunc-fma.h"
+
+libc_ifunc_redirected (__redirect_ieee754_atanh, __ieee754_atanh, IFUNC_SELECTOR ());
+
+libm_alias_finite (__ieee754_atanh, __atanh)
+
+# define __ieee754_atanh __ieee754_atanh_sse2
+#endif
+#include <sysdeps/ieee754/dbl-64/e_atanh.c>