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, 36 insertions, 3 deletions

diff --git a/gcc/c-decl.c b/gcc/c-decl.c
index b6ff3f476e6..bc90fdd38dd 100644
--- a/gcc/c-decl.c
+++ b/gcc/c-decl.c
@@ -1164,14 +1164,21 @@ pop_scope (void)
 
 	case VAR_DECL:
 	  /* Warnings for unused variables.  */
-	  if (!TREE_USED (p)
+	  if ((!TREE_USED (p) || !DECL_READ_P (p))
 	      && !TREE_NO_WARNING (p)
 	      && !DECL_IN_SYSTEM_HEADER (p)
 	      && DECL_NAME (p)
 	      && !DECL_ARTIFICIAL (p)
 	      && scope != file_scope
 	      && scope != external_scope)
-	    warning (OPT_Wunused_variable, "unused variable %q+D", p);
+	    {
+	      if (!TREE_USED (p))
+		warning (OPT_Wunused_variable, "unused variable %q+D", p);
+	      else if (DECL_CONTEXT (p) == current_function_decl)
+		warning_at (DECL_SOURCE_LOCATION (p),
+			    OPT_Wunused_but_set_variable,
+			    "variable %qD set but not used", p);
+	    }
 
 	  if (b->inner_comp)
 	    {
@@ -2387,6 +2394,8 @@ merge_decls (tree newdecl, tree olddecl, tree newtype, tree oldtype)
     TREE_USED (newdecl) = 1;
   else if (TREE_USED (newdecl))
     TREE_USED (olddecl) = 1;
+  if (TREE_CODE (olddecl) == VAR_DECL || TREE_CODE (olddecl) == PARM_DECL)
+    DECL_READ_P (newdecl) |= DECL_READ_P (olddecl);
   if (DECL_PRESERVE_P (olddecl))
     DECL_PRESERVE_P (newdecl) = 1;
   else if (DECL_PRESERVE_P (newdecl))
@@ -4232,7 +4241,10 @@ finish_decl (tree decl, location_t init_loc, tree init,
 	}
 
       if (TREE_USED (type))
-	TREE_USED (decl) = 1;
+	{
+	  TREE_USED (decl) = 1;
+	  DECL_READ_P (decl) = 1;
+	}
     }
 
   /* If this is a function and an assembler name is specified, reset DECL_RTL
@@ -4380,6 +4392,7 @@ finish_decl (tree decl, location_t init_loc, tree init,
 	  /* Don't warn about decl unused; the cleanup uses it.  */
 	  TREE_USED (decl) = 1;
 	  TREE_USED (cleanup_decl) = 1;
+	  DECL_READ_P (decl) = 1;
 
 	  push_cleanup (decl, cleanup, false);
 	}
@@ -4472,6 +4485,7 @@ build_compound_literal (location_t loc, tree type, tree init, bool non_const)
   TREE_STATIC (decl) = (current_scope == file_scope);
   DECL_CONTEXT (decl) = current_function_decl;
   TREE_USED (decl) = 1;
+  DECL_READ_P (decl) = 1;
   TREE_TYPE (decl) = type;
   TREE_READONLY (decl) = TYPE_READONLY (type);
   store_init_value (loc, decl, init, NULL_TREE);
@@ -8060,6 +8074,25 @@ finish_function (void)
       TREE_NO_WARNING (fndecl) = 1;
     }
 
+  /* Complain about parameters that are only set, but never otherwise used.  */
+  if (warn_unused_but_set_parameter)
+    {
+      tree decl;
+
+      for (decl = DECL_ARGUMENTS (fndecl);
+	   decl;
+	   decl = TREE_CHAIN (decl))
+	if (TREE_USED (decl)
+	    && TREE_CODE (decl) == PARM_DECL
+	    && !DECL_READ_P (decl)
+	    && DECL_NAME (decl)
+	    && !DECL_ARTIFICIAL (decl)
+	    && !TREE_NO_WARNING (decl))
+	  warning_at (DECL_SOURCE_LOCATION (decl),
+		      OPT_Wunused_but_set_parameter,
+		      "parameter %qD set but not used", decl);
+    }
+
   /* Store the end of the function, so that we get good line number
      info for the epilogue.  */
   cfun->function_end_locus = input_location;