Revert of Remove register index/code indirection

src/mips64/lithium-codegen-mips64.cc

Index: src/mips64/lithium-codegen-mips64.cc
diff --git a/src/mips64/lithium-codegen-mips64.cc b/src/mips64/lithium-codegen-mips64.cc
index 22a06e8e120d2aee865791862929c04bdb772bcd..4c76551138e0801aca4b23d10a913f44561e745a 100644
--- a/src/mips64/lithium-codegen-mips64.cc
+++ b/src/mips64/lithium-codegen-mips64.cc
@@ -71,7 +71,7 @@
   BitVector* doubles = chunk()->allocated_double_registers();
   BitVector::Iterator save_iterator(doubles);
   while (!save_iterator.Done()) {
-    __ sdc1(DoubleRegister::from_code(save_iterator.Current()),
+    __ sdc1(DoubleRegister::FromAllocationIndex(save_iterator.Current()),
             MemOperand(sp, count * kDoubleSize));
     save_iterator.Advance();
     count++;
@@ -87,7 +87,7 @@
   BitVector::Iterator save_iterator(doubles);
   int count = 0;
   while (!save_iterator.Done()) {
-    __ ldc1(DoubleRegister::from_code(save_iterator.Current()),
+    __ ldc1(DoubleRegister::FromAllocationIndex(save_iterator.Current()),
             MemOperand(sp, count * kDoubleSize));
     save_iterator.Advance();
     count++;
@@ -386,12 +386,12 @@
 
 
 Register LCodeGen::ToRegister(int index) const {
-  return Register::from_code(index);
+  return Register::FromAllocationIndex(index);
 }
 
 
 DoubleRegister LCodeGen::ToDoubleRegister(int index) const {
-  return DoubleRegister::from_code(index);
+  return DoubleRegister::FromAllocationIndex(index);
 }