Revert of Remove register index/code indirection

src/compiler/register-allocator-verifier.cc

Index: src/compiler/register-allocator-verifier.cc
diff --git a/src/compiler/register-allocator-verifier.cc b/src/compiler/register-allocator-verifier.cc
index 3b595b3b45d98d6222a8d44bb04e991db46f9695..0b775d29e1d83620eb1bc9504a5e8dd315f2dbbb 100644
--- a/src/compiler/register-allocator-verifier.cc
+++ b/src/compiler/register-allocator-verifier.cc
@@ -218,16 +218,14 @@
       return;
     case kFixedRegister:
       CHECK(op->IsRegister());
-      CHECK_EQ(RegisterOperand::cast(op)->GetDoubleRegister().code(),
-               constraint->value_);
+      CHECK_EQ(RegisterOperand::cast(op)->index(), constraint->value_);
       return;
     case kDoubleRegister:
       CHECK(op->IsDoubleRegister());
       return;
     case kFixedDoubleRegister:
       CHECK(op->IsDoubleRegister());
-      CHECK_EQ(DoubleRegisterOperand::cast(op)->GetDoubleRegister().code(),
-               constraint->value_);
+      CHECK_EQ(DoubleRegisterOperand::cast(op)->index(), constraint->value_);
       return;
     case kFixedSlot:
       CHECK(op->IsStackSlot());