Revert "Revert "Fully support pairs in the register allocator.""

This reverts commit c399fdc442db82dfda66e6c25518872ab0f1d24f.

Change-Id: I19f8215c4b98f2f0827e04bf7806c3ca439794e5
diff --git a/compiler/optimizing/graph_visualizer.cc b/compiler/optimizing/graph_visualizer.cc
index 9e0a5b8..df21c8e 100644
--- a/compiler/optimizing/graph_visualizer.cc
+++ b/compiler/optimizing/graph_visualizer.cc
@@ -142,6 +142,10 @@
       codegen_.DumpFloatingPointRegister(output_, location.low());
       output_ << " and ";
       codegen_.DumpFloatingPointRegister(output_, location.high());
+    } else if (location.IsRegisterPair()) {
+      codegen_.DumpCoreRegister(output_, location.low());
+      output_ << " and ";
+      codegen_.DumpCoreRegister(output_, location.high());
     } else {
       DCHECK(location.IsDoubleStackSlot());
       output_ << "2x" << location.GetStackIndex() << "(sp)";