[libiberty] Make test for variables more robust

[Eric Botcazou]

Hi,

the test for the presence of variables (really symbols) does not work when you 
add -Ox -flto to CFLAGS:

  for v in $vars; do
AC_MSG_CHECKING([for $v])
AC_CACHE_VAL(libiberty_cv_var_$v,
  [AC_LINK_IFELSE([AC_LANG_PROGRAM([[int *p;]],[[extern int $v []; p = 
$v;]])],
  [eval "libiberty_cv_var_$v=yes"],
  [eval "libiberty_cv_var_$v=no"])])
if eval "test \"`echo '$libiberty_cv_var_'$v`\" = yes"; then
  AC_MSG_RESULT(yes)
  n=HAVE_`echo $v | tr 'abcdefghijklmnopqrstuvwxyz' 
'ABCDEFGHIJKLMNOPQRSTUVWXYZ'`
  AC_DEFINE_UNQUOTED($n)
else
  AC_MSG_RESULT(no)
fi
  done

because the assignment to 'p' is optimized away by LTO.  This is visible on 
MinGW platforms in the form of a link failure for sys_siglist.

Tested on x86-64/Linux, x86-64/Windows and x86/Windows, OK for the mainline?


2021-05-03  Eric Botcazou  

* configure.ac: Make test for variables more robust.
* configure: Regenerate.

-- 
Eric Botcazoudiff --git a/libiberty/configure.ac b/libiberty/configure.ac
index ad952963971..3c03f24d368 100644
--- a/libiberty/configure.ac
+++ b/libiberty/configure.ac
@@ -665,7 +665,7 @@ if test -z "${setobjs}"; then
   for v in $vars; do
 AC_MSG_CHECKING([for $v])
 AC_CACHE_VAL(libiberty_cv_var_$v,
-  [AC_LINK_IFELSE([AC_LANG_PROGRAM([[int *p;]],[[extern int $v []; p = $v;]])],
+  [AC_LINK_IFELSE([AC_LANG_PROGRAM([[extern int $v [];]],[[if ($v [0]) return 1;]])],
 		  [eval "libiberty_cv_var_$v=yes"],
 		  [eval "libiberty_cv_var_$v=no"])])
 if eval "test \"`echo '$libiberty_cv_var_'$v`\" = yes"; then

Re: [libiberty] Make test for variables more robust

[Richard Biener via Gcc-patches]

On Mon, May 3, 2021 at 9:51 AM Eric Botcazou  wrote:
>
> Hi,
>
> the test for the presence of variables (really symbols) does not work when you
> add -Ox -flto to CFLAGS:
>
>   for v in $vars; do
> AC_MSG_CHECKING([for $v])
> AC_CACHE_VAL(libiberty_cv_var_$v,
>   [AC_LINK_IFELSE([AC_LANG_PROGRAM([[int *p;]],[[extern int $v []; p =
> $v;]])],
>   [eval "libiberty_cv_var_$v=yes"],
>   [eval "libiberty_cv_var_$v=no"])])
> if eval "test \"`echo '$libiberty_cv_var_'$v`\" = yes"; then
>   AC_MSG_RESULT(yes)
>   n=HAVE_`echo $v | tr 'abcdefghijklmnopqrstuvwxyz'
> 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'`
>   AC_DEFINE_UNQUOTED($n)
> else
>   AC_MSG_RESULT(no)
> fi
>   done
>
> because the assignment to 'p' is optimized away by LTO.  This is visible on
> MinGW platforms in the form of a link failure for sys_siglist.
>
> Tested on x86-64/Linux, x86-64/Windows and x86/Windows, OK for the mainline?

OK.

>
> 2021-05-03  Eric Botcazou  
>
> * configure.ac: Make test for variables more robust.
> * configure: Regenerate.
>
> --
> Eric Botcazou