PR c++/84686 - missing volatile loads.

	* cvt.c (convert_to_void): Call maybe_undo_parenthesized_ref.

From-SVN: r258231

gcc/cp/ChangeLog

+2018-03-03  Jason Merrill  <jason@redhat.com>
+
+	PR c++/84686 - missing volatile loads.
+	* cvt.c (convert_to_void): Call maybe_undo_parenthesized_ref.
+
 2018-03-03  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/71464

gcc/cp/cvt.c

@@ -1063,6 +1063,8 @@ convert_to_void (tree expr, impl_conv_void implicit, tsubst_flags_t complain)
       || TREE_TYPE (expr) == error_mark_node)
     return error_mark_node;
 
+  expr = maybe_undo_parenthesized_ref (expr);
+
   expr = mark_discarded_use (expr);
   if (implicit == ICV_CAST)
     /* An explicit cast to void avoids all -Wunused-but-set* warnings.  */

gcc/testsuite/g++.dg/tree-ssa/volatile2.C

+// PR c++/84686
+// { dg-additional-options -fdump-tree-gimple }
+// { dg-final { scan-tree-dump-times "= i" 10 "gimple" } }
+
+volatile int i;
+
+int main()
+{
+  i; //evaluated (a load is performed)
+  (i); //unevaluated => the load shall be performed
+
+  (void)i; //evaluated (a load is performed)
+  (void)(i); //unevaluated => the load shall be performed
+
+  (void)i; //evaluated (a load is performed)
+  (void)(i); //unevaluated => the load shall be performed
+
+  (i,i); // the two subexpression are evaluated
+  ((i),(i)); // no evaluation, => two loads shall happen
+}