loop-init.c (loop_optimizer_init, [...]): Do not destroy dominance information.

	* loop-init.c (loop_optimizer_init, loop_optimizer_finalize): Do not
	destroy dominance information.
	* passes.c (rest_of_handle_loop2):  Free dominance information.
	* tree-cfg.c (cleanup_tree_cfg): Remove unreachable blocks before
	jump threading.
	(thread_jumps): Update dominance information and remove unreachable
	blocks.
	* tree-ssa-phiopt.c (replace_phi_with_stmt):  Update dominance
	information and remove the unreachable block.

From-SVN: r84873