# ===========================================================================

#             http://www.nongnu.org/autoconf-archive/ax_tls.html

# ===========================================================================

#

# SYNOPSIS

#

#   AX_TLS

#

# DESCRIPTION

#

#   Provides a test for the compiler support of thread local storage (TLS)

#   extensions. Defines TLS if it is found. Currently only knows about GCC

#   and MSVC. I think SunPro uses the same as GCC, and Borland apparently

#   supports either.

#

# LICENSE

#

#   Copyright (c) 2008 Alan Woodland <ajw05@aber.ac.uk>

#

#   This program is free software: you can redistribute it and/or modify it

#   under the terms of the GNU General Public License as published by the

#   Free Software Foundation, either version 3 of the License, or (at your

#   option) any later version.

#

#   This program is distributed in the hope that it will be useful, but

#   WITHOUT ANY WARRANTY; without even the implied warranty of

#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General

#   Public License for more details.

#

#   You should have received a copy of the GNU General Public License along

#   with this program. If not, see <http://www.gnu.org/licenses/>.

#

#   As a special exception, the respective Autoconf Macro's copyright owner

#   gives unlimited permission to copy, distribute and modify the configure

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#   need not follow the terms of the GNU General Public License when using

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#   Macro appear in them. The GNU General Public License (GPL) does govern

#   all other use of the material that constitutes the Autoconf Macro.

#

#   This special exception to the GPL applies to versions of the Autoconf

#   Macro released by the Autoconf Archive. When you make and distribute a

#   modified version of the Autoconf Macro, you may extend this special

#   exception to the GPL to apply to your modified version as well.

AC_DEFUN([AX_TLS], [

  AC_MSG_CHECKING(for thread local storage specifier)

  AC_CACHE_VAL(ac_cv_tls, [

    ax_tls_keywords="__thread __declspec(thread) none"

    for ax_tls_keyword in $ax_tls_keywords; do

       case $ax_tls_keyword in

          none) ac_cv_tls=none ; break ;;

	  *)

             # MPICH modification: This was an AC_TRY_COMPILE before, but

             # Darwin with non-standard compilers will accept __thread at

             # compile time but fail to link due to an undefined

             # "__emutls_get_address" symbol unless -lgcc_eh is added to the

             # link line.

             AC_LINK_IFELSE(

                 [AC_LANG_PROGRAM([$ax_tls_keyword int bar = 5;],[++bar;])],

                 [ac_cv_tls=$ax_tls_keyword],

                 [ac_cv_tls=none])

	     # MPICH modification: Also test with the extern keyword.

	     # The intel compiler on Darwin (at least as of 15.0.1)

	     # seems to break with the above error when the extern

	     # keyword is specified in shared library builds.

	     PAC_PUSH_FLAG([LIBS])

	     PAC_APPEND_FLAG([-shared],[LIBS])

	     if test "$ac_cv_tls" != "none" ; then

                AC_LINK_IFELSE(

			[AC_LANG_PROGRAM([extern $ax_tls_keyword int bar;],[++bar;])],

                        [ac_cv_tls=$ax_tls_keyword],

                        [ac_cv_tls=none])

	     fi

	     PAC_POP_FLAG([LIBS])

	     if test "$ac_cv_tls" != "none" ; then break ; fi

          esac

    done

])

  if test "$ac_cv_tls" != "none"; then

    # MPICH modification: this was "TLS" before instead of

    # "MPICH_TLS_SPECIFIER", but TLS had a reasonably high chance of conflicting

    # with a system library.

    AC_DEFINE_UNQUOTED([MPICH_TLS_SPECIFIER], $ac_cv_tls, [If the compiler supports a TLS storage class define it to that here])

  fi

  AC_MSG_RESULT($ac_cv_tls)

])