x86_64: Add exp2m1f with FMA

The CORE-MATH exp2m1f implementation showed slight worse latency
when using x86_64 baseline ABI.  This patch adds a ifunc variant
with similar performance for x86_64-v3.

Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
Reviewed-by: DJ Delorie <dj@redhat.com>

sysdeps/ieee754/flt-32/s_exp2m1f.c

@@ -189,4 +189,6 @@ __exp2m1f (float x)
       return (s - 1.0) + w * c0;
     }
 }
+#ifndef __exp2m1f
 libm_alias_float (__exp2m1, exp2m1)
+#endif

sysdeps/x86_64/fpu/multiarch/Makefile

@@ -12,6 +12,7 @@ CFLAGS-s_sin-fma.c = -mfma -mavx2
 CFLAGS-s_tan-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
 
 CFLAGS-e_exp2f-fma.c = -mfma -mavx2
 CFLAGS-e_expf-fma.c = -mfma -mavx2
@@ -74,6 +75,7 @@ libm-sysdep_routines += \
   s_cosf-fma \
   s_cosf-sse2 \
   s_exp10m1f-fma \
+  s_exp2m1f-fma \
   s_expm1-fma \
   s_floor-sse4_1 \
   s_floorf-sse4_1 \

sysdeps/x86_64/fpu/multiarch/s_exp2m1f-fma.c

@@ -0,0 +1,4 @@
+#define __exp2m1f __exp2m1f_fma
+#define SECTION __attribute__ ((section (".text.fma")))
+
+#include <sysdeps/ieee754/flt-32/s_exp2m1f.c>

sysdeps/x86_64/fpu/multiarch/s_exp2m1f.c

@@ -0,0 +1,33 @@
+/* Multiple versions of exp2m1.
+   Copyright (C) 2024 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-float.h>
+
+extern float __redirect_exp2m1f (float);
+
+# define SYMBOL_NAME exp2m1f
+# include "ifunc-fma.h"
+
+libc_ifunc_redirected (__redirect_exp2m1f, __exp2m1f, IFUNC_SELECTOR ());
+libm_alias_float (__exp2m1, exp2m1)
+
+# define __exp2m1f __exp2m1f_sse2
+#endif
+#include <sysdeps/ieee754/flt-32/s_exp2m1f.c>