x86_64: Remove bzero optimization

Both symbols are marked as legacy in POSIX.1-2001 and removed on
POSIX.1-2008, although the prototypes are defined for _GNU_SOURCE
or _DEFAULT_SOURCE.

GCC also replaces bcopy with a memmove and bzero with memset on default
configuration (to actually get a bzero libc call the code requires
to omit string.h inclusion and built with -fno-builtin), so it is
highly unlikely programs are actually calling libc bzero symbol.

On a recent Linux distro (Ubuntu 22.04), there is no bzero calls
by the installed binaries.

  $ cat count_bstring.sh
  #!/bin/bash

  files=`IFS=':';for i in $PATH; do test -d "$i" && find "$i" -maxdepth 1 -executable -type f; done`
  total=0
  for file in $files; do
    symbols=`objdump -R $file 2>&1`
    if [ $? -eq 0 ]; then
      ncalls=`echo $symbols | grep -w $1 | wc -l`
      ((total=total+ncalls))
      if [ $ncalls -gt 0 ]; then
        echo "$file: $ncalls"
      fi
    fi
  done
  echo "TOTAL=$total"
  $ ./count_bstring.sh bzero
  TOTAL=0

Checked on x86_64-linux-gnu.

1 files changed, 0 insertions, 6 deletions

diff --git a/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
index a093a2831f..c0bf2875d0 100644
--- a/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
+++ b/sysdeps/x86_64/multiarch/memset-avx2-unaligned-erms.S
@@ -14,9 +14,6 @@
   vmovd d, %xmm0; \
   movq r, %rax;
 
-# define BZERO_ZERO_VEC0() \
-  vpxor %xmm0, %xmm0, %xmm0
-
 # define WMEMSET_SET_VEC0_AND_SET_RETURN(d, r) \
   MEMSET_SET_VEC0_AND_SET_RETURN(d, r)
 
@@ -32,9 +29,6 @@
 # ifndef MEMSET_SYMBOL
 #  define MEMSET_SYMBOL(p,s)	p##_avx2_##s
 # endif
-# ifndef BZERO_SYMBOL
-#  define BZERO_SYMBOL(p,s)	p##_avx2_##s
-# endif
 # ifndef WMEMSET_SYMBOL
 #  define WMEMSET_SYMBOL(p,s)	p##_avx2_##s
 # endif