Remove TARGET_RELAXED_ORDERING and optimize for weak memory models.

Remove TARGET_RELAXED_ORDERING and optimize for weak memory models.

This patch removes the special casing for targets with relaxed
memory ordering and handles guard accesses with equivalent
atomic load acquire operations. In this process we change the
algorithm to load the guard variable with an atomic load that
has ACQUIRE semantics.

This then means that on targets which have weak memory models, the
fast path is inlined and can directly use a load-acquire instruction
where available (and yay! one more hook gone).

2015-06-04  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>

	PR c++/66192
	PR target/66200
	* doc/tm.texi: Regenerate.
	* doc/tm.texi.in (TARGET_RELAXED_ORDERING): Delete.
	* target.def (TARGET_RELAXED_ORDERING): Likewise.
	* config/alpha/alpha.c (TARGET_RELAXED_ORDERING): Likewise.
	* config/ia64/ia64.c (TARGET_RELAXED_ORDERING): Likewise.
	* config/rs6000/rs6000.c (TARGET_RELAXED_ORDERING): Likewise.
	* config/sparc/linux.h (SPARC_RELAXED_ORDERING): Likewise.
	* config/sparc/linux64.h (SPARC_RELAXED_ORDERING): Likewise.
	* config/sparc/sparc.c (TARGET_RELAXED_ORDERING): Likewise.
	* config/sparc/sparc.h (SPARC_RELAXED_ORDERING): Likewise.
	* system.h (TARGET_RELAXED_ORDERING): Poison.

2015-06-04  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>

	PR c++/66192
	PR target/66200
	* cp-tree.h (get_guard_cond): Adjust declaration
	* decl.c (expand_static_init): Use atomic load acquire
	and adjust call to get_guard_cond.
	* decl2.c (build_atomic_load_byte): New function.
	(get_guard_cond): Handle thread_safety.
	(one_static_initialization_or_destruction): Adjust call to
	get_guard_cond.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@224118 138bc75d-0d04-0410-961f-82ee72b054a4