2011-07-25  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/49822
	* tree-ssa-forwprop.c (remove_prop_source_from_use): Robustify
	more.  Make sure to preserve stmts with side-effects.  Properly
	handle virtual defs, follow a longer def chain.

From-SVN: r176745