re PR c++/50158 (invalid 'variable set but not used' warning (boolean used as an…

re PR c++/50158 (invalid 'variable set but not used' warning (boolean used as an index to an array))

	PR c++/50158
	* typeck.c (cp_build_modify_expr): Call mark_rvalue_use on rhs
	if it has side-effects and needs to be preevaluated.

	* g++.dg/warn/Wunused-var-16.C: New test.

From-SVN: r177992

gcc/cp/ChangeLog

+2011-08-23  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/50158
+	* typeck.c (cp_build_modify_expr): Call mark_rvalue_use on rhs
+	if it has side-effects and needs to be preevaluated.
+
 2011-08-23  Siddhesh Poyarekar  <siddhesh.poyarekar@gmail.com>
 
 	PR c++/50055

gcc/cp/typeck.c

@@ -6692,6 +6692,8 @@ cp_build_modify_expr (tree lhs, enum tree_code modifycode, tree rhs,
 	     side effect associated with any single compound assignment
 	     operator. -- end note ]  */
 	  lhs = stabilize_reference (lhs);
+	  if (TREE_SIDE_EFFECTS (rhs))
+	    rhs = mark_rvalue_use (rhs);
 	  rhs = stabilize_expr (rhs, &init);
 	  newrhs = cp_build_binary_op (input_location,
 				       modifycode, lhs, rhs,

gcc/testsuite/ChangeLog

 2011-08-23  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/50158
+	* g++.dg/warn/Wunused-var-16.C: New test.
+
 	PR middle-end/50161
 	* gcc.dg/pr50161.c: New test.
 

gcc/testsuite/g++.dg/warn/Wunused-var-16.C

+// PR c++/50158
+// { dg-do compile }
+// { dg-options "-Wunused" }
+
+int bar (int);
+
+int
+foo (int a)
+{
+  int b[] = { a, -a };
+  a += b[bar (a) < a];
+  return a;
+}