re PR c/18624 (GCC does not detect local variable set but never used)

	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.

From-SVN: r158086

1 files changed, 8 insertions, 1 deletions

diff --git a/gcc/tree.h b/gcc/tree.h
index 4a0fb5e..96c9575 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -1317,6 +1317,9 @@ extern void omp_clause_range_check_failed (const_tree, const char *, int,
   (TREE_CHECK3 (NODE, VAR_DECL, PARM_DECL, \
 		RESULT_DECL)->decl_common.decl_restricted_flag)
 
+#define DECL_READ_P(NODE) \
+  (TREE_CHECK2 (NODE, VAR_DECL, PARM_DECL)->decl_common.decl_read_flag)
+
 /* In a CALL_EXPR, means that the call is the jump from a thunk to the
    thunked-to function.  */
 #define CALL_FROM_THUNK_P(NODE) (CALL_EXPR_CHECK (NODE)->base.protected_flag)
@@ -2691,8 +2694,12 @@ struct GTY(()) tree_decl_common {
   /* In VAR_DECL, PARM_DECL and RESULT_DECL, this is DECL_RESTRICTED_P.  */
   unsigned decl_restricted_flag : 1;
 
+  /* In VAR_DECL and PARM_DECL set when the decl has been used except for
+     being set.  */
+  unsigned decl_read_flag : 1;
+
   /* Padding so that 'off_align' can be on a 32-bit boundary.  */
-  unsigned decl_common_unused : 2;
+  unsigned decl_common_unused : 1;
 
   /* DECL_OFFSET_ALIGN, used only for FIELD_DECLs.  */
   unsigned int off_align : 8;