config: Remove HAVE_BUILTIN_MEMSET macro

  s patch removed HAVE_BUILTIN_MEMSET macro because GCC 6.2 that is
minimum requirement to compile glibc already support
__builtin_memset()[1].

Interestingly, removed code had a critical bug that is
HAVE_BUILTIN_MEMSET macro never be defined, because yes/no assignment
to libc_cv_gcc_builtin_memset was reversed in configure.ac as below:

1519 if AC_TRY_COMMAND([${CC-cc} -O3 -S conftest.c -o - | grep -F "memset" > /dev/null]);
1520 then
1521   libc_cv_gcc_builtin_memset=no   # shold be yes
1522 else
1523   libc_cv_gcc_builtin_memset=yes  # should be no
1524 fi
1525 rm -f conftest* ])
1526 if test "$libc_cv_gcc_builtin_memset" = yes ; then
1527   AC_DEFINE(HAVE_BUILTIN_MEMSET)
1528 fi

Therefor __builtin_memset() in elf/rtld.c was never be compiled.

 534 # ifdef HAVE_BUILTIN_MEMSET
 535   __builtin_memset (bootstrap_map.l_info, '\0', sizeof (bootstrap_map.l_info));
 536 # else

[1] https://gcc.gnu.org/onlinedocs/gcc-6.2.0/gcc/Other-Builtins.html
---
 config.h.in  |  3 ---
 configure    | 31 -------------------------------
 configure.ac | 19 -------------------
 elf/rtld.c   | 15 ++++-----------
 4 files changed, 4 insertions(+), 64 deletions(-)
  

I'll fix the typo

> s patch removed HAVE_BUILTIN_MEMSET macro because GCC 6.2 that is

s/s/This/

> minimum requirement to compile glibc already support
>__builtin_memset()[1].

Thanks.
Naohiro
  

On Jul 26 2021, Naohiro Tamura via Libc-alpha wrote:

> Interestingly, removed code had a critical bug that is
> HAVE_BUILTIN_MEMSET macro never be defined, because yes/no assignment
> to libc_cv_gcc_builtin_memset was reversed in configure.ac as below:

No, the point of the check is that __buildin_memset does *not* expand to
a memset libcall, as explained in the comment you removed.

Andreas.
  

Hi Andreas,

Thank you for the comment.

> From: Andreas Schwab <schwab@linux-m68k.org>

> On Jul 26 2021, Naohiro Tamura via Libc-alpha wrote:
> 
> > Interestingly, removed code had a critical bug that is
> > HAVE_BUILTIN_MEMSET macro never be defined, because yes/no assignment
> > to libc_cv_gcc_builtin_memset was reversed in configure.ac as below:
> 
> No, the point of the check is that __buildin_memset does *not* expand to
> a memset libcall, as explained in the comment you removed.
> 

Is the comment you mentioned below?

   /* 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.  */
+     make function calls at this point.  Use '__builtin_memset' instead.
+     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.  */

Do you mean that yes/no assignment to libc_cv_gcc_builtin_memset was NOT reversed?
If it was not reversed, config.h never had " #define HAVE_BUILTIN_MEMSET 1" 
even if gcc 8.3 is used.

Thanks.
Naohiro
  

On Jul 26 2021, naohirot@fujitsu.com wrote:

> If it was not reversed, config.h never had " #define HAVE_BUILTIN_MEMSET 1" 
> even if gcc 8.3 is used.

This is correct if the builtin just expands to a memset libcall.

Andreas.
  

Hi Andreas,

Thanks for the explanation.

> From: Andreas Schwab <schwab@linux-m68k.org>

> > If it was not reversed, config.h never had " #define HAVE_BUILTIN_MEMSET 1"
> > even if gcc 8.3 is used.
>
> This is correct if the builtin just expands to a memset libcall.

Now I understood that by looking at the grep argument again in the line below:

1519 if AC_TRY_COMMAND([${CC-cc} -O3 -S conftest.c -o - | grep -F "memset" > /dev/null]);

So the macro name "HAVE_BUILTIN_MEMSET" is very confusing,
since GCC 6.2 manual mentions that __builtin_memset is supported.
Can we agree to change it to "HAVE_NON_LIB_EXPAND_BUILTIN_MEMSET"  or "HAVE_NON_LIBCALL_BUILTIN_MEMSET"?

Thanks.
Naohiro