Update pretty printer for std::variant

	* python/libstdcxx/v6/printers.py (StdVariantPrinter): Adjust for
	recent change to _Variant_storage.
	* testsuite/libstdc++-prettyprinters/cxx17.cc: Test variant with
	reference type.

From-SVN: r240345

libstdc++-v3/ChangeLog

 2016-09-22  Jonathan Wakely  <jwakely@redhat.com>
 
+	* python/libstdcxx/v6/printers.py (StdVariantPrinter): Adjust for
+	recent change to _Variant_storage.
+	* testsuite/libstdc++-prettyprinters/cxx17.cc: Test variant with
+	reference type.
+
 	* include/bits/uses_allocator.h (__uses_allocator_construct): Qualify
 	std::forward and ::new. Cast pointer to void*.
 	* include/std/variant (_Variant_storage, _Union, _Variant_base)

libstdc++-v3/python/libstdcxx/v6/printers.py

@@ -994,7 +994,7 @@ class StdVariantPrinter(SingleObjContainerPrinter):
             visualizer = None
         else:
             self.contained_type = alternatives[int(self.index)]
-            addr = val['_M_first']['_M_storage'].address
+            addr = val['_M_union']['_M_first']['_M_storage'].address
             contained_value = addr.cast(self.contained_type.pointer()).dereference()
             visualizer = gdb.default_visualizer(contained_value)
         super (StdVariantPrinter, self).__init__(contained_value, visualizer, 'array')

libstdc++-v3/testsuite/libstdc++-prettyprinters/cxx17.cc

@@ -84,6 +84,9 @@ main()
   variant<float, int, string_view> v4{ str };
 // { dg-final { note-test v4 {std::variant<float, int, std::string_view> [index 2] = {"string"}} } }
 
+  variant<string_view&> vref{str};
+// { dg-final { note-test vref {std::variant<std::basic_string_view<char, std::char_traits<char> > &> [index 0] = {"string"}} } }
+
   std::cout << "\n";
   return 0;			// Mark SPOT
 }