C++ PATCH for c++/61392 (ICE mangling member without object)

[Jason Merrill]

This code was first allowed by DR 850: as of C++11, in unevaluated 
context it's OK to refer to a non-static data member without an 
associated object.  The ABI says that this is mangled like an unresolved 
name, i.e. as the plain identifier.

Tested x86_64-pc-linux-gnu, applying to trunk.
commit e6a6cf41c76af773e573c00d8e7314c1223b0cff
Author: Jason Merrill <ja...@redhat.com>
Date:   Fri Sep 19 06:15:02 2014 -0400
    	PR c++/61392
    	* mangle.c (write_expression): Use unresolved-name mangling for
    	DR850 case.

diff --git a/gcc/cp/mangle.c b/gcc/cp/mangle.c
index 5c201d6..1642da5 100644
--- a/gcc/cp/mangle.c
+++ b/gcc/cp/mangle.c
@@ -2866,11 +2866,16 @@ write_expression (tree expr)
 	    {
 	      write_string (operator_name_info[(int)code].mangled_name);
 	      ob = TREE_OPERAND (ob, 0);
+	      write_expression (ob);
 	    }
-	  else
-	    write_string ("dt");
+	  else if (!is_dummy_object (ob))
+	    {
+	      write_string ("dt");
+	      write_expression (ob);
+	    }
+	  /* else, for a non-static data member with no associated object (in
+	     unevaluated context), use the unresolved-name mangling.  */
 
-	  write_expression (ob);
 	  write_member_name (TREE_OPERAND (expr, 1));
 	  return;
 	}
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index bcf161b..1d81028 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -1685,7 +1685,7 @@ finish_non_static_data_member (tree decl, tree object, tree qualifying_scope)
   if (object == error_mark_node)
     return error_mark_node;
 
-  /* DR 613: Can use non-static data members without an associated
+  /* DR 613/850: Can use non-static data members without an associated
      object in sizeof/decltype/alignof.  */
   if (is_dummy_object (object) && cp_unevaluated_operand == 0
       && (!processing_template_decl || !current_class_ref))
diff --git a/gcc/testsuite/g++.dg/abi/mangle63.C b/gcc/testsuite/g++.dg/abi/mangle63.C
new file mode 100644
index 0000000..d6a58a3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/abi/mangle63.C
@@ -0,0 +1,11 @@
+// DR 850 makes this valid
+// { dg-do compile { target c++11 } }
+
+template<class T> struct A
+{
+  int mem;
+  template<class U> decltype(U()+mem) f();
+};
+int i = A<int>().f<int>();
+
+// { dg-final { scan-assembler "_ZN1AIiE1fIiEEDTplcvT__E3memEv" } }