x86_64: Add log1p with FMA

On Skylake, it changes log1p bench performance by:

        Before       After     Improvement
max     63.349       58.347       8%
min     4.448        5.651        -30%
mean    12.0674      10.336       14%

The minimum code path is

 if (hx < 0x3FDA827A)                          /* x < 0.41422  */
    {
      if (__glibc_unlikely (ax >= 0x3ff00000))           /* x <= -1.0 */
        {
	   ...
        }
      if (__glibc_unlikely (ax < 0x3e200000))           /* |x| < 2**-29 */
        {
          math_force_eval (two54 + x);          /* raise inexact */
          if (ax < 0x3c900000)                  /* |x| < 2**-54 */
            {
	      ...
            }
          else
            return x - x * x * 0.5;

FMA and non-FMA code sequences look similar.  Non-FMA version is slightly
faster.  Since log1p is called by asinh and atanh, it improves asinh
performance by:

        Before       After     Improvement
max     75.645       63.135       16%
min     10.074       10.071       0%
mean    15.9483      14.9089      6%

and improves atanh performance by:

        Before       After     Improvement
max     91.768       75.081       18%
min     15.548       13.883       10%
mean    18.3713      16.8011      8%

1 files changed, 29 insertions, 0 deletions

diff --git a/sysdeps/x86_64/fpu/multiarch/s_log1p.c b/sysdeps/x86_64/fpu/multiarch/s_log1p.c
new file mode 100644
index 0000000000..6ce5198d6d
--- /dev/null
+++ b/sysdeps/x86_64/fpu/multiarch/s_log1p.c
@@ -0,0 +1,29 @@
+/* Multiple versions of log1p.
+   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_log1p (double);
+
+#define SYMBOL_NAME log1p
+#include "ifunc-fma.h"
+
+libc_ifunc_redirected (__redirect_log1p, __log1p, IFUNC_SELECTOR ());
+
+#define __log1p __log1p_sse2
+#include <sysdeps/ieee754/dbl-64/s_log1p.c>