x86: Optimize and shrink st{r|p}{n}{cat|cpy}-evex functions

Optimizations are:
    1. Use more overlapping stores to avoid branches.
    2. Reduce how unrolled the aligning copies are (this is more of a
       code-size save, its a negative for some sizes in terms of
       perf).
    3. Improve the loop a bit (similiar to what we do in strlen with
       2x vpminu + kortest instead of 3x vpminu + kmov + test).
    4. For st{r|p}n{cat|cpy} re-order the branches to minimize the
       number that are taken.

Performance Changes:

    Times are from N = 10 runs of the benchmark suite and are
    reported as geometric mean of all ratios of
    New Implementation / Old Implementation.

    stpcpy-evex      -> 0.922
    strcat-evex      -> 0.985
    strcpy-evex      -> 0.880

    strncpy-evex     -> 0.831
    stpncpy-evex     -> 0.780

    strncat-evex     -> 0.958

Code Size Changes:
    function         -> Bytes New / Bytes Old -> Ratio

    strcat-evex      ->  819 / 1874 -> 0.437
    strcpy-evex      ->  700 / 1074 -> 0.652
    stpcpy-evex      ->  735 / 1094 -> 0.672

    strncpy-evex     -> 1397 / 2611 -> 0.535
    stpncpy-evex     -> 1489 / 2691 -> 0.553

    strncat-evex     -> 1184 / 2832 -> 0.418

Notes:
    1. Because of the significant difference between the
       implementations they are split into three files.

           strcpy-evex.S    -> strcpy, stpcpy, strcat
           strncpy-evex.S   -> strncpy
           strncat-evex.S    > strncat

       I couldn't find a way to merge them without making the
       ifdefs incredibly difficult to follow.

    2. All implementations can be made evex512 by including
       "x86-evex512-vecs.h" at the top.

    3. All implementations have an optional define:
        `USE_EVEX_MASKED_STORE`
       Setting to one uses evex-masked stores for handling short
       strings.  This saves code size and branches.  It's disabled
       for all implementations are the moment as there are some
       serious drawbacks to masked stores in certain cases, but
       that may be fixed on future architectures.

Full check passes on x86-64 and build succeeds for all ISA levels w/
and w/o multiarch.

1 files changed, 80 insertions, 0 deletions

diff --git a/sysdeps/x86_64/multiarch/strncpy-or-cat-overflow-def.h b/sysdeps/x86_64/multiarch/strncpy-or-cat-overflow-def.h
new file mode 100644
index 0000000000..d4f4d6c82b
--- /dev/null
+++ b/sysdeps/x86_64/multiarch/strncpy-or-cat-overflow-def.h
@@ -0,0 +1,80 @@
+/* Helper for getting proper name of overflow fallback function for
+   {wc|st}{p|r|s}n{cat|cpy}
+
+   All versions must be listed in ifunc-impl-list.c.
+   Copyright (C) 2022 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/>.  */
+
+#ifndef _STRNCPY_OR_CAT_OVERFLOW_DEF_H_
+#define _STRNCPY_OR_CAT_OVERFLOW_DEF_H_ 1
+
+#if defined USE_MULTIARCH && IS_IN(libc)
+#  define UNDERSCORES __
+#  ifdef USE_WITH_SSE2
+#    define ISA_EXT _sse2
+#  elif defined USE_WITH_AVX2
+#    ifdef USE_WITH_RTM
+#      define ISA_EXT _avx2_rtm
+#    else
+#      define ISA_EXT _avx2
+#    endif
+
+#  elif defined USE_WITH_EVEX256
+#    define ISA_EXT _evex
+#  elif defined USE_WITH_EVEX512
+#    define ISA_EXT _evex512
+#  endif
+#else
+#  define UNDERSCORES
+#  define ISA_EXT
+#endif
+
+#ifdef USE_AS_WCSCPY
+#  define STRCPY_PREFIX wc
+#  define STRCAT_PREFIX wcs
+#  ifdef USE_AS_STPCPY
+#    define STRCPY_POSTFIX pcpy
+#  else
+#    define STRCPY_POSTFIX scpy
+#  endif
+#else
+#  define STRCPY_PREFIX st
+#  define STRCAT_PREFIX str
+#  ifdef USE_AS_STPCPY
+#    define STRCPY_POSTFIX pcpy
+#  else
+#    define STRCPY_POSTFIX rcpy
+#  endif
+#endif
+#define STRCAT_POSTFIX cat
+
+#define PRIMITIVE_OF_NAMER(underscores, prefix, postfix, ext)                 \
+  underscores##prefix##postfix##ext
+
+#define OF_NAMER(...) PRIMITIVE_OF_NAMER (__VA_ARGS__)
+
+#ifndef OVERFLOW_STRCPY
+#  define OVERFLOW_STRCPY                                                     \
+    OF_NAMER (UNDERSCORES, STRCPY_PREFIX, STRCPY_POSTFIX, ISA_EXT)
+#endif
+
+#ifndef OVERFLOW_STRCAT
+#  define OVERFLOW_STRCAT                                                     \
+    OF_NAMER (UNDERSCORES, STRCAT_PREFIX, STRCAT_POSTFIX, ISA_EXT)
+#endif
+
+#endif