re PR tree-optimization/77855 (wrong code at -O3 on x86_64-linux-gnu (in both 32-bit and 64-bit modes))

2016-10-06  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/77855
	* tree-ssa-pre.c (prune_clobbered_mems): Queue exprs to remove
	instead of removing the current item while iterating over the set
	which is not safe.

	* gcc.dg/torture/pr77855.c: New testcase.

From-SVN: r240832