re PR c++/83806 (Spurious -Wunused-but-set-parameter with nullptr)

/cp
2018-02-08  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/83806
	* typeck.c (decay_conversion): Use mark_rvalue_use for the special
	case of nullptr too.

/testsuite
2018-02-08  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/83806
	* g++.dg/warn/Wunused-parm-11.C: New.

From-SVN: r257502

gcc/cp/ChangeLog

+2018-02-08  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	PR c++/83806
+	* typeck.c (decay_conversion): Use mark_rvalue_use for the special
+	case of nullptr too.
+
 2018-02-08  Nathan Sidwell  <nathan@acm.org>
 
 	* class.c (finish_struct): Fix std:initializer_list diagnostic

gcc/cp/typeck.c

@@ -2009,7 +2009,10 @@ decay_conversion (tree exp,
     return error_mark_node;
 
   if (NULLPTR_TYPE_P (type) && !TREE_SIDE_EFFECTS (exp))
-    return nullptr_node;
+    {
+      mark_rvalue_use (exp, loc, reject_builtin);
+      return nullptr_node;
+    }
 
   /* build_c_cast puts on a NOP_EXPR to make the result not an lvalue.
      Leave such NOP_EXPRs, since RHS is being used in non-lvalue context.  */

gcc/testsuite/ChangeLog

+2018-02-08  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	PR c++/83806
+	* g++.dg/warn/Wunused-parm-11.C: New.
+
 2018-02-08  Marek Polacek  <polacek@redhat.com>
 
 	PR tree-optimization/84238

gcc/testsuite/g++.dg/warn/Wunused-parm-11.C

+// PR c++/83806
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wunused-but-set-parameter" }
+
+template <class X, class Y>
+bool equals(X x, Y y) {
+    return (x == y); 
+}
+
+int main() {
+    const char* p = nullptr;
+    equals(p, nullptr);
+}