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dnl Check whether the target supports TLS.

AC_DEFUN([GCC_CHECK_TLS], [

  GCC_ENABLE(tls, yes, [Use thread-local storage])

  AC_CACHE_CHECK([whether the target supports thread-local storage],

                 have_tls, [

    AC_RUN_IFELSE([__thread int a; int b; int main() { return a = b; }],

      [dnl If the test case passed with dynamic linking, try again with

      dnl static linking.  This fails at least with some older Red Hat

      dnl releases.

      save_LDFLAGS="$LDFLAGS"

      LDFLAGS="-static $LDFLAGS"

      AC_RUN_IFELSE([__thread int a; int b; int main() { return a = b; }],

                    [have_tls=yes], [have_tls=no], [])

      LDFLAGS="$save_LDFLAGS"],

      [have_tls=no],

      [AC_COMPILE_IFELSE([__thread int foo;], [have_tls=yes], [have_tls=no])]

    )])

  if test "$enable_tls $have_tls" = "yes yes"; then

    AC_DEFINE(HAVE_TLS, 1,

              [Define to 1 if the target supports thread-local storage.])

  fi])