PR c/18624

	* tree.h (DECL_READ_P): Define.
	(struct tree_decl_common): Add decl_read_flag.
	* c-decl.c (pop_scope): If TREE_USED but !DECL_READ_P, issue
	a set but not used warning.
	(merge_decls): Merge DECL_READ_P flag.
	(finish_decl, build_compound_literal): Set DECL_READ_P flag.
	(finish_function): Issue -Wunused-but-set-parameter diagnostics.
	* c-common.c (handle_used_attribute, handle_unused_attribute):
	Likewise.
	* c-tree.h (default_function_array_read_conversion, mark_exp_read):
	New prototypes.
	* c-typeck.c (default_function_array_read_conversion, mark_exp_read):
	New functions.
	(default_conversion, c_process_expr_stmt): Call mark_exp_read.
	* c-parser.c (c_parser_initializer, c_parser_expr_no_commas,
	c_parser_binary_expression, c_parser_cast_expression,
	c_parser_expr_list, c_parser_omp_atomic, c_parser_omp_for_loop):
	Call default_function_array_read_conversion instead of
	default_function_array_conversion where needed.
	(c_parser_unary_expression, c_parser_conditional_expression,
	c_parser_postfix_expression_after_primary, c_parser_initelt):
	Likewise.  Call mark_exp_read where needed.
	(c_parser_statement_after_labels, c_parser_asm_operands,
	c_parser_typeof_specifier, c_parser_sizeof_expression,
	c_parser_alignof_expression, c_parser_initval): Call mark_exp_read
	where needed.
	* common.opt (Wunused-but-set-variable, Wunused-but-set-parameter):
	New.
	* toplev.c (warn_unused_but_set_variable): Default to warn_unused.
	(warn_unused_but_set_parameter): Default to warn_unused
	&& extra_warnings.
	* doc/invoke.texi: Document -Wunused-but-set-variable and
	-Wunused-but-set-parameter.

	* objc-act.c (finish_var_decl, objc_begin_catch_clause,
	really_start_method, get_super_receiver, handle_class_ref): Set
	DECL_READ_P in addition to TREE_USED.

	* gcc.dg/Wunused-var-1.c: New test.
	* gcc.dg/Wunused-var-2.c: New test.
	* gcc.dg/Wunused-var-3.c: New test.
	* gcc.dg/Wunused-var-4.c: New test.
	* gcc.dg/Wunused-var-5.c: New test.
	* gcc.dg/Wunused-var-6.c: New test.
	* gcc.dg/Wunused-parm-1.c: New test.


git-svn-id: https://gcc.gnu.org/svn/gcc/trunk@158086 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 8 insertions, 1 deletions

diff --git a/gcc/c-common.c b/gcc/c-common.c
index 7daba6bfea1..32dc21e93af 100644
--- a/gcc/c-common.c
+++ b/gcc/c-common.c
@@ -6121,6 +6121,8 @@ handle_used_attribute (tree *pnode, tree name, tree ARG_UNUSED (args),
     {
       TREE_USED (node) = 1;
       DECL_PRESERVE_P (node) = 1;
+      if (TREE_CODE (node) == VAR_DECL)
+	DECL_READ_P (node) = 1;
     }
   else
     {
@@ -6147,7 +6149,12 @@ handle_unused_attribute (tree *node, tree name, tree ARG_UNUSED (args),
 	  || TREE_CODE (decl) == FUNCTION_DECL
 	  || TREE_CODE (decl) == LABEL_DECL
 	  || TREE_CODE (decl) == TYPE_DECL)
-	TREE_USED (decl) = 1;
+	{
+	  TREE_USED (decl) = 1;
+	  if (TREE_CODE (decl) == VAR_DECL
+	      || TREE_CODE (decl) == PARM_DECL)
+	    DECL_READ_P (decl) = 1;
+	}
       else
 	{
 	  warning (OPT_Wattributes, "%qE attribute ignored", name);