re PR c++/44062 ((void)var; doesn't prevent 'set but not used' warning)

	PR c++/44062
	* c-parser.c (c_parser_expression): Mark LHS of a comma
	expression as read if it is a decl, handled component or
	COMPOUND_EXPR with that on the RHS.
	* c-typeck.c (c_process_expr_stmt): Mark RHS of COMPOUND_EXPR
	if it is a decl or handled component.

	* semantics.c (finish_expr_stmt): Don't call mark_exp_read here...
	* cvt.c (convert_to_void): ... but here.  If expr is a COMPOUND_EXPR,
	look at its second operand.

	* c-c++-common/Wunused-var-7.c: New test.
	* g++.dg/warn/Wunused-var-9.C: New test.

From-SVN: r159286

gcc/ChangeLog

+2010-05-11  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/44062
+	* c-parser.c (c_parser_expression): Mark LHS of a comma
+	expression as read if it is a decl, handled component or
+	COMPOUND_EXPR with that on the RHS.
+	* c-typeck.c (c_process_expr_stmt): Mark RHS of COMPOUND_EXPR
+	if it is a decl or handled component.
+
 2010-05-11  Jan Hubicka  <jh@suse.cz>
 
 	* lto-symtab.c (lto_symtab_free): New function.

gcc/c-parser.c

@@ -6028,10 +6028,16 @@ c_parser_expression (c_parser *parser)
   while (c_parser_next_token_is (parser, CPP_COMMA))
     {
       struct c_expr next;
+      tree lhsval;
       location_t loc = c_parser_peek_token (parser)->location;
       location_t expr_loc;
       c_parser_consume_token (parser);
       expr_loc = c_parser_peek_token (parser)->location;
+      lhsval = expr.value;
+      while (TREE_CODE (lhsval) == COMPOUND_EXPR)
+	lhsval = TREE_OPERAND (lhsval, 1);
+      if (DECL_P (lhsval) || handled_component_p (lhsval))
+	mark_exp_read (lhsval);
       next = c_parser_expr_no_commas (parser, NULL);
       next = default_function_array_conversion (expr_loc, next);
       expr.value = build_compound_expr (loc, expr.value, next.value);

gcc/c-typeck.c

@@ -8841,6 +8841,8 @@ emit_side_effect_warnings (location_t loc, tree expr)
 tree
 c_process_expr_stmt (location_t loc, tree expr)
 {
+  tree exprv;
+
   if (!expr)
     return NULL_TREE;
 
@@ -8861,8 +8863,11 @@ c_process_expr_stmt (location_t loc, tree expr)
       && warn_unused_value)
     emit_side_effect_warnings (loc, expr);
 
-  if (DECL_P (expr) || handled_component_p (expr))
-    mark_exp_read (expr);
+  exprv = expr;
+  while (TREE_CODE (exprv) == COMPOUND_EXPR)
+    exprv = TREE_OPERAND (exprv, 1);
+  if (DECL_P (exprv) || handled_component_p (exprv))
+    mark_exp_read (exprv);
 
   /* If the expression is not of a type to which we cannot assign a line
      number, wrap the thing in a no-op NOP_EXPR.  */

gcc/cp/ChangeLog

+2010-05-11  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/44062
+	* semantics.c (finish_expr_stmt): Don't call mark_exp_read here...
+	* cvt.c (convert_to_void): ... but here.  If expr is a COMPOUND_EXPR,
+	look at its second operand.
+
 2010-05-10  Jason Merrill  <jason@redhat.com>
 
 	PR c++/44017

gcc/cp/cvt.c

 /* Language-level data type conversion for GNU C++.
    Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
-   1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
+   1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
    Free Software Foundation, Inc.
    Hacked by Michael Tiemann (tiemann@cygnus.com)
 
@@ -822,9 +822,23 @@ ocp_convert (tree type, tree expr, int convtype, int flags)
 tree
 convert_to_void (tree expr, const char *implicit, tsubst_flags_t complain)
 {
+  tree exprv;
+
   if (expr == error_mark_node
       || TREE_TYPE (expr) == error_mark_node)
     return error_mark_node;
+
+  exprv = expr;
+  while (TREE_CODE (exprv) == COMPOUND_EXPR)
+    exprv = TREE_OPERAND (exprv, 1);
+  if (DECL_P (exprv) || handled_component_p (exprv))
+    /* Expr is not being 'used' here, otherwise we whould have
+       called mark_{rl}value_use use here, which would have in turn
+       called mark_exp_read.  Rather, we call mark_exp_read directly
+       to avoid some warnings when
+       -Wunused-but-set-{variable,parameter} is in effect.  */
+    mark_exp_read (exprv);
+
   if (!TREE_TYPE (expr))
     return expr;
   if (invalid_nonstatic_memfn_p (expr, complain))

gcc/cp/semantics.c

@@ -4,7 +4,7 @@
    and during the instantiation of template functions.
 
    Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007,
-		 2008, 2009 Free Software Foundation, Inc.
+		 2008, 2009, 2010 Free Software Foundation, Inc.
    Written by Mark Mitchell (mmitchell@usa.net) based on code found
    formerly in parse.y and pt.c.
 
@@ -610,13 +610,6 @@ finish_expr_stmt (tree expr)
 	{
 	  if (warn_sequence_point)
 	    verify_sequence_points (expr);
-	  if (TREE_CODE (expr) != MODIFY_EXPR)
-	    /* Expr is not being 'used' here, otherwise we whould have
-	       called mark_{rl}value_use use here, which would have in turn
-	       called mark_exp_read. Rather, we call mark_exp_read directly
-	       to avoid some warnings when
-	        -Wunused-but-set-{variable,parameter} is in effect.  */
-	    mark_exp_read (expr);
 	  expr = convert_to_void (expr, "statement", tf_warning_or_error);
 	}
       else if (!type_dependent_expression_p (expr))

gcc/testsuite/ChangeLog

+2010-05-11  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/44062
+	* c-c++-common/Wunused-var-7.c: New test.
+	* g++.dg/warn/Wunused-var-9.C: New test.
+
 2010-05-11  Daniel Franke  <franke.daniel@gmail.com>
 
         PR fortran/43711

gcc/testsuite/c-c++-common/Wunused-var-7.c

+/* PR c++/44062 */
+/* { dg-do compile } */
+/* { dg-options "-Wunused" } */
+
+void
+foo (void)
+{
+  int a, b, c, d, e, f, g;
+  a = 1;
+  b = 2;
+  c = 3;
+  d = 4;
+  e = 5;
+  f = 6;
+  g = 7;
+  a;			/* { dg-warning "no effect" } */
+  b, 1;			/* { dg-warning "no effect" } */
+  (void) c;
+  (void) d, 1;		/* { dg-warning "no effect" } */
+  e, f, 1;		/* { dg-warning "no effect" } */
+  (void) g, f, 1;	/* { dg-warning "no effect" } */
+}
+
+void
+bar (void)
+{
+  int a;
+  int b;
+  int c;		/* { dg-warning "set but not used" } */
+  a = 1;
+  b = 2;
+  c = 3;
+  c = ({ a++, b; });
+}
+
+void
+baz (void)
+{
+  int a;
+  int b;
+  int c;
+  int d;
+  a = 1;
+  b = 2;
+  c = 3;
+  d = 4;
+  d, ( a++, b ), c;	/* { dg-warning "no effect" } */
+}

gcc/testsuite/g++.dg/warn/Wunused-var-9.C

+/* PR c++/44062 */
+/* { dg-do compile } */
+/* { dg-options "-Wunused" } */
+
+void
+f ()
+{
+  int i = 4;
+  static_cast <void> (i);
+  int j;
+  j = 5;
+  static_cast <void> (j);
+}