* c-common.c (handle_warn_unused_result_attribute): New function.
	(c_common_attribute_table): Add warn_unused_result.
	(c_expand_expr): Issue warning when result of inlined function
	with warn_unused_result attribute is ignored.
	* calls.c (expand_call): Issue warning when result of function
	with warn_unused_result attribute is ignored.
	* c-common.h (STMT_EXPR_WARN_UNUSED_RESULT): Define.
	* expr.c (expr_wfl_stack): Define.
	(expand_expr) <case EXPR_WITH_FILE_LOCATION>: If ignore,
	pass const0_rtx as target.  Chain locations into expr_wfl_stack.
	* tree-inline.c (expand_call_inline): Set STMT_EXPR_WARN_UNUSED_RESULT
	bit if inlined function has warn_unused_result attribute.
	* input.h (expr_wfl_stack): Declare.
	* doc/extend.texi: Document warn_unused_result attribute.

	* gcc.dg/attr-warn-unused-result.c: New test.

Co-Authored-By: Jakub Jelinek <jakub@redhat.com>

From-SVN: r71424