[PATCH] Remove more backedge threading support

[PATCH] Remove more backedge threading support

	* tree-ssa-threadedge.c (dummy_simplify): Remove.
	(thread_around_empty_blocks): Remove backedge_seen_p argument.
	If we thread to a backedge, then return false.  Update recursive
	call to eliminate backedge_seen_p argument.
	(thread_through_normal_block): Remove backedge_seen_p argument.
	Remove backedge_seen_p argument from calls to
	thread_around_empty_blocks.  Remove checks on backedge_seen_p.
	If we thread to a backedge, then return 0.
	(thread_across_edge): Remove bookkeeping for backedge_seen.  Don't
	pass it to thread_through_normal_block or thread_through_empty_blocks.
	For joiner handling, if we see a backedge, do not try normal
	threading.

From-SVN: r229911