Re: [PATCH v3 5/5] config: Rename HAVE_BUILTIN_MEMSET macro

[Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>]

On 05/08/2021 04:52, Naohiro Tamura via Libc-alpha wrote:
> This patch renames HAVE_BUILTIN_MEMSET macro to
> HAVE_NON_LIB_EXPAND_BUILTIN_MEMSET.
> 
> The name "HAVE_BUILTIN_MEMSET" is very confusing.
> This macro cannot be removed even though GCC 6.2, that is minimum
> requirement to compile glibc, already supports __builtin_memset[1].
> It doesn't indicate whether GCC supports __builtin_memset or not.
> 
> But it indicates whether GCC supports __builtin_memset which doesn't
> expand to a memset libcall or not.
> 
> Therefor HAVE_NON_LIB_EXPAND_BUILTIN_MEMSET is more appropriate to
> increase code readability.
> 
> [1] https://gcc.gnu.org/onlinedocs/gcc-6.2.0/gcc/Other-Builtins.html

Sorry, but I don't see much gain in renaming the internal variable.  I agree
with the comment improvement.

> ---
>  config.h.in  |  4 ++--
>  configure    | 14 +++++++-------
>  configure.ac | 10 +++++-----
>  elf/rtld.c   |  9 +++++----
>  4 files changed, 19 insertions(+), 18 deletions(-)
> 
> diff --git a/config.h.in b/config.h.in
> index 8b45a3a61d77..4700dc9eba9b 100644
> --- a/config.h.in
> +++ b/config.h.in
> @@ -40,8 +40,8 @@
>     shared between GNU libc and GNU gettext projects.  */
>  #define HAVE_BUILTIN_EXPECT 1
>  
> -/* Define if the compiler supports __builtin_memset.  */
> -#undef	HAVE_BUILTIN_MEMSET
> +/* Define if the compiler supports non lib expand __builtin_memset.  */
> +#undef	HAVE_NON_LIB_EXPAND_BUILTIN_MEMSET
>  
>  /* Define if compiler accepts -ftree-loop-distribute-patterns.  */
>  #undef  HAVE_CC_INHIBIT_LOOP_TO_LIBCALL

Ok.

> diff --git a/configure b/configure
> index 9619c10991d0..224c754cf466 100755
> --- a/configure
> +++ b/configure
> @@ -6263,7 +6263,7 @@ fi
>  
>  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for __builtin_memset" >&5
>  $as_echo_n "checking for __builtin_memset... " >&6; }
> -if ${libc_cv_gcc_builtin_memset+:} false; then :
> +if ${libc_cv_gcc_non_lib_expand_builtin_memset+:} false; then :
>    $as_echo_n "(cached) " >&6
>  else
>    cat > conftest.c <<\EOF
> @@ -6279,16 +6279,16 @@ if { ac_try='${CC-cc} -O3 -S conftest.c -o - | grep -F "memset" > /dev/null'
>    $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
>    test $ac_status = 0; }; };
>  then
> -  libc_cv_gcc_builtin_memset=no
> +  libc_cv_gcc_non_lib_expand_builtin_memset=no
>  else
> -  libc_cv_gcc_builtin_memset=yes
> +  libc_cv_gcc_non_lib_expand_builtin_memset=yes
>  fi
>  rm -f conftest*
>  fi
> -{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gcc_builtin_memset" >&5
> -$as_echo "$libc_cv_gcc_builtin_memset" >&6; }
> -if test "$libc_cv_gcc_builtin_memset" = yes ; then
> -  $as_echo "#define HAVE_BUILTIN_MEMSET 1" >>confdefs.h
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gcc_non_lib_expand_builtin_memset" >&5
> +$as_echo "$libc_cv_gcc_non_lib_expand_builtin_memset" >&6; }
> +if test "$libc_cv_gcc_non_lib_expand_builtin_memset" = yes ; then
> +  $as_echo "#define HAVE_NON_LIB_EXPAND_BUILTIN_MEMSET 1" >>confdefs.h
>  
>  fi
>  
> diff --git a/configure.ac b/configure.ac
> index 34ecbba54054..451cea7683e6 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -1508,7 +1508,7 @@ if test $libc_cv_have_section_quotes = yes; then
>    AC_DEFINE(HAVE_SECTION_QUOTES)
>  fi
>  
> -AC_CACHE_CHECK(for __builtin_memset, libc_cv_gcc_builtin_memset, [dnl
> +AC_CACHE_CHECK(for __builtin_memset, libc_cv_gcc_non_lib_expand_builtin_memset, [dnl
>  cat > conftest.c <<\EOF
>  void zero (void *x)
>  {
> @@ -1518,13 +1518,13 @@ EOF
>  dnl
>  if AC_TRY_COMMAND([${CC-cc} -O3 -S conftest.c -o - | grep -F "memset" > /dev/null]);
>  then
> -  libc_cv_gcc_builtin_memset=no
> +  libc_cv_gcc_non_lib_expand_builtin_memset=no
>  else
> -  libc_cv_gcc_builtin_memset=yes
> +  libc_cv_gcc_non_lib_expand_builtin_memset=yes
>  fi
>  rm -f conftest* ])
> -if test "$libc_cv_gcc_builtin_memset" = yes ; then
> -  AC_DEFINE(HAVE_BUILTIN_MEMSET)
> +if test "$libc_cv_gcc_non_lib_expand_builtin_memset" = yes ; then
> +  AC_DEFINE(HAVE_NON_LIB_EXPAND_BUILTIN_MEMSET)
>  fi
>  
>  AC_CACHE_CHECK(for redirection of built-in functions, libc_cv_gcc_builtin_redirection, [dnl

I see no point in rename it, a better comment as you are doing is suffice.

> diff --git a/elf/rtld.c b/elf/rtld.c
> index d733359eaf80..a18494fcd38e 100644
> --- a/elf/rtld.c
> +++ b/elf/rtld.c
> @@ -527,11 +527,12 @@ _dl_start (void *arg)
>    /* Partly clean the `bootstrap_map' structure up.  Don't use
>       `memset' since it might not be built in or inlined and we cannot
>       make function calls at this point.  Use '__builtin_memset' if we
> -     know it is available.  We do not have to clear the memory if we
> -     do not have to use the temporary bootstrap_map.  Global variables
> -     are initialized to zero by default.  */
> +     know it is available and does not expand to a memset libcall.
> +     We do not have to clear the memory if we do not have to use the
> +     temporary bootstrap_map.  Global variables are initialized to
> +     zero by default.  */
>  #ifndef DONT_USE_BOOTSTRAP_MAP
> -# ifdef HAVE_BUILTIN_MEMSET
> +# ifdef HAVE_NON_LIB_EXPAND_BUILTIN_MEMSET
>    __builtin_memset (bootstrap_map.l_info, '\0', sizeof (bootstrap_map.l_info));
>  # else
>    for (size_t cnt = 0;
> 

Ok.