* tree-ssa-threadedge.c (record_temporary_equivalence): Handle
	NULL for RHS, which we used to invalidate equivalences.
	(record_temporary_equivalences_from_phis): New bitmap arguments
	and a boolean indicating if we have passed a backedge.  If we
	have passed a backedge, then set the appropriate bit in the
	bitmaps for the SRC & DEST of PHIs creating equivalences.
	(invalidate_equivalences, dummy_simplify): New functions.
	(cond_arg_set_in_b): Remove.
	(record_temporary_equivalences_from_stmts_at_dest): New bitmap
	arguments and a boolean indicating if we have passed a backedge.
	If we have passed a backedge, then perform invalidations as
	needed.
	(thread_around_empty_blocks): If we have seen a backedge, then
	use the dummy simplify routine.
	(thread_through_normal_block): Likewise.  Pass bitmaps and
	backedge status to children.  Do not pessimize so much when
	traversing backedges in the CFG.
	(thread_across_edge): Manage the SRC_MAP/DST_MAP bitmaps.
	If we have seen a backedge, then use the dummy simplify routine.
	Do not pessimize so much when traversing backedges.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@205279 138bc75d-0d04-0410-961f-82ee72b054a4