tree-ssa-pre.c (eliminate_dom_walker::before_dom_children): Skip unreachable blocks and destinations.

2017-05-11  Richard Biener  <rguenther@suse.de>

	* tree-ssa-pre.c (eliminate_dom_walker::before_dom_children):
	Skip unreachable blocks and destinations.
	(eliminate): Move stmt removal and fixup ...
	(fini_eliminate): ... here.  Skip inserted exprs.
	(pass_pre::execute): Move fini_pre after fini_eliminate.
	* tree-ssa-tailmerge.c: Include tree-cfgcleanup.h.
	(tail_merge_optimize): Run cleanup_tree_cfg if requested by
	PRE to get rid of dead code that has invalid SSA form and
	split critical edges again.

From-SVN: r247882