tree-ssa-forwprop.c (remove_prop_source_from_use): Robustify against already removed statements.

2011-07-20  Richard Guenther  <rguenther@suse.de>

	* tree-ssa-forwprop.c (remove_prop_source_from_use): Robustify
	against already removed statements.
	(forward_propagate_into_comparison): Remove dead defining stmts.
	(forward_propagate_into_gimple_cond): Likewise.
	(forward_propagate_into_cond): Simplify.
	(ssa_forward_propagate_and_combine): Handle changed cfg from
	forward_propagate_into_comparison.
	* tree-ssa-phiopt.c (conditional_replacement): Use proper
	locations for newly built statements.

From-SVN: r176517