[PATCH] Improve DOM's optimization of control statements

[PATCH] Improve DOM's optimization of control statements

	* tree-ssa-dom.c (optimize_stmt): Collapse control flow statements
	with constant conditions.
	* tree-ssa-threadupdate.c (remove_jump_threads_starting_at): New.
	(remove_ctrl_stmt_and_useless_edges): No longer static.
	* tree-ssa-threadupdate.h (remove_jump_threads_starting_at): Prototype.
	(remove_ctrl_stmt_and_useless_edges): Likewise.

	* gcc.dg/tree-ssa/ssa-dom-branch-1.c: New test.

From-SVN: r228306