Fix off by one errors in linear scan register allocator.

Change-Id: I65eea3cc125e12106a7160d30cb91c5d173bd405
diff --git a/compiler/optimizing/code_generator_x86_64.cc b/compiler/optimizing/code_generator_x86_64.cc
index 9e63f8b..6174ac6 100644
--- a/compiler/optimizing/code_generator_x86_64.cc
+++ b/compiler/optimizing/code_generator_x86_64.cc
@@ -1831,7 +1831,7 @@
     } else if (destination.IsFpuRegister()) {
       __ movsd(destination.As<XmmRegister>(), Address(CpuRegister(RSP), source.GetStackIndex()));
     } else {
-      DCHECK(destination.IsDoubleStackSlot());
+      DCHECK(destination.IsDoubleStackSlot()) << destination;
       __ movq(CpuRegister(TMP), Address(CpuRegister(RSP), source.GetStackIndex()));
       __ movq(Address(CpuRegister(RSP), destination.GetStackIndex()), CpuRegister(TMP));
     }