2011-09-08  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/19831
	* tree-ssa-dce.c (mark_all_reaching_defs_necessary_1): Also
	skip builtins with vdefs that do not really store something.
	(propagate_necessity): For calls to free that we can associate
	with an allocation function do not mark the freed pointer
	definition necessary.
	(eliminate_unnecessary_stmts): Remove a call to free if
	the associated call to an allocation function is not necessary.

	* gcc.dg/tree-ssa/pr19831-1.c: New testcase.
	* gcc.dg/tree-ssa/pr19831-2.c: Likewise.
	* gcc.dg/tree-ssa/pr19831-3.c: Likewise.
	* gcc.dg/errno-1.c: Adjust.

From-SVN: r178687