Support longs in the register allocator for x86_64.

Change-Id: I7fb6dfb761bc5cf9e5705682032855a0a70ca867
diff --git a/compiler/optimizing/graph_visualizer.cc b/compiler/optimizing/graph_visualizer.cc
index a49ce64..f033e2e 100644
--- a/compiler/optimizing/graph_visualizer.cc
+++ b/compiler/optimizing/graph_visualizer.cc
@@ -108,9 +108,11 @@
       } else {
         codegen_.DumpCoreRegister(output_, location.reg().RegId());
       }
-    } else {
-      DCHECK(location.IsStackSlot());
+    } else if (location.IsStackSlot()) {
       output_ << location.GetStackIndex() << "(sp)";
+    } else {
+      DCHECK(location.IsDoubleStackSlot());
+      output_ << "2x" << location.GetStackIndex() << "(sp)";
     }
   }