2013-10-09  Marc Glisse  <marc.glisse@inria.fr>

	PR tree-optimization/20318
gcc/c-family/
	* c-common.c (handle_returns_nonnull_attribute): New function.
	(c_common_attribute_table): Add returns_nonnull.

gcc/
	* doc/extend.texi (returns_nonnull): New function attribute.
	* fold-const.c (tree_expr_nonzero_warnv_p): Look for returns_nonnull
	attribute.
	* tree-vrp.c (gimple_stmt_nonzero_warnv_p): Likewise.
	(stmt_interesting_for_vrp): Accept all GIMPLE_CALL.

gcc/testsuite/
	* c-c++-common/pr20318.c: New file.
	* gcc.dg/tree-ssa/pr20318.c: New file.

From-SVN: r203316