AArch64 - use CSDB based sequences if speculation tracking is enabled

AArch64 - use CSDB based sequences if speculation tracking is enabled

In this final patch, now that we can track speculation through conditional
branches, we can use this information to use a less expensive CSDB based
speculation barrier.

	* config/aarch64/iterators.md (ALLI_TI): New iterator.
	* config/aarch64/aarch64.md (despeculate_copy<ALLI_TI:mode>): New
	expand.
	(despeculate_copy<ALLI:mode>_insn): New insn.
	(despeculate_copyti_insn): New insn.
	(despeculate_simple<ALLI:mode>): New insn
	(despeculate_simpleti): New insn.
	* config/aarch64/aarch64.c (aarch64_speculation_safe_value): New
	function.
	(TARGET_SPECULATION_SAFE_VALUE): Redefine to
	aarch64_speculation_safe_value.
	(aarch64_print_operand): Handle const0_rtx in modifier 'H'.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@263174 138bc75d-0d04-0410-961f-82ee72b054a4