Revert of Remove register index/code indirection

src/compiler/code-generator-impl.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_CODE_GENERATOR_IMPL_H_
 #define V8_COMPILER_CODE_GENERATOR_IMPL_H_
 
 #include "src/code-stubs.h"
 #include "src/compiler/code-generator.h"
 #include "src/compiler/instruction.h"
@@ skipping 76 matching lines @@
 
   Label* ToLabel(InstructionOperand* op) {
     return gen_->GetLabel(ToRpoNumber(op));
   }
 
   RpoNumber ToRpoNumber(InstructionOperand* op) {
     return ToConstant(op).ToRpoNumber();
   }
 
   Register ToRegister(InstructionOperand* op) {
-    return RegisterOperand::cast(op)->GetRegister();
+    return Register::FromAllocationIndex(RegisterOperand::cast(op)->index());
   }
 
   DoubleRegister ToDoubleRegister(InstructionOperand* op) {
-    return DoubleRegisterOperand::cast(op)->GetDoubleRegister();
+    return DoubleRegister::FromAllocationIndex(
+        DoubleRegisterOperand::cast(op)->index());
   }
 
   Constant ToConstant(InstructionOperand* op) {
     if (op->IsImmediate()) {
       return gen_->code()->GetImmediate(ImmediateOperand::cast(op));
     }
     return gen_->code()->GetConstant(
         ConstantOperand::cast(op)->virtual_register());
   }
 
@@ skipping 46 matching lines @@
 #elif V8_TARGET_ARCH_IA32 || V8_TARGET_ARCH_X64
   masm->ud2();
 #endif
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_CODE_GENERATOR_IMPL_H