provides a mechanism for optimizing compilers to select the different Register configuration.

src/compiler/instruction.cc

Index: src/compiler/instruction.cc
diff --git a/src/compiler/instruction.cc b/src/compiler/instruction.cc
index 5f02f11efde297bfca8f266172353a37d5859568..2727779e6836b395f0f8edaedf2fdb20e6309368 100644
--- a/src/compiler/instruction.cc
+++ b/src/compiler/instruction.cc
@@ -272,8 +272,8 @@ void ReferenceMap::RecordReference(const AllocatedOperand& op) {
 std::ostream& operator<<(std::ostream& os, const ReferenceMap& pm) {
   os << "{";
   bool first = true;
-  PrintableInstructionOperand poi = {RegisterConfiguration::ArchDefault(),
-                                     InstructionOperand()};
+  PrintableInstructionOperand poi = {
+      RegisterConfiguration::ArchDefault(TURBOFAN), InstructionOperand()};
   for (auto& op : pm.reference_operands_) {
     if (!first) {
       os << ";";