PR c++/80840 - ICE with constexpr and reference

	* pt.c (convert_nontype_argument): Don't test whether a decl is
	value-dependent when binding to a reference.

From-SVN: r248749

gcc/cp/ChangeLog

+2017-05-31  Jason Merrill  <jason@redhat.com>
+
+	PR c++/80840 - ICE with constexpr and reference
+	* pt.c (convert_nontype_argument): Don't test whether a decl is
+	value-dependent when binding to a reference.
+
 2017-05-31  Nathan Sidwell  <nathan@acm.org>
 
 	* cp-tree.h (lang_decl_slector): New enum.

gcc/cp/pt.c

@@ -6749,7 +6749,11 @@ convert_nontype_argument (tree type, tree expr, tsubst_flags_t complain)
 	    }
 	}
 
-      if (!value_dependent_expression_p (expr))
+      if (TYPE_REF_OBJ_P (TREE_TYPE (expr))
+	  && value_dependent_expression_p (expr))
+	/* OK, dependent reference.  We don't want to ask whether a DECL is
+	   itself value-dependent, since what we want here is its address.  */;
+      else
 	{
 	  if (!DECL_P (expr))
 	    {
@@ -6771,8 +6775,11 @@ convert_nontype_argument (tree type, tree expr, tsubst_flags_t complain)
 	      return NULL_TREE;
 	    }
 
-	  expr = build_nop (type, build_address (expr));
+	  expr = build_address (expr);
 	}
+
+      if (!same_type_p (type, TREE_TYPE (expr)))
+	expr = build_nop (type, expr);
     }
   /* [temp.arg.nontype]/5, bullet 4
 

gcc/testsuite/g++.dg/template/ref10.C

+// PR c++/80840
+// { dg-do compile { target c++11 } }
+
+template <class T, T X>
+struct Just;
+
+template <const double& X>
+struct Number {
+    static constexpr double value = X;
+    using result = Just<const double&, value>;
+};
+
+int main() {}