The IC exposes a register definition.

src/x64/stub-cache-x64.cc

 // Copyright 2012 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.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/arguments.h"
 #include "src/codegen.h"
@@ skipping 1204 matching lines @@
   __ LoadRoot(rax, Heap::kUndefinedValueRootIndex);
   __ ret(0);
 
   // Return the generated code.
   return GetCode(kind(), Code::FAST, name);
 }
 
 
 Register* LoadStubCompiler::registers() {
   // receiver, name, scratch1, scratch2, scratch3, scratch4.
-  static Register registers[] = { rax, rcx, rdx, rbx, rdi, r8 };
+  Register receiver = LoadIC::ReceiverRegister();
+  Register name = LoadIC::NameRegister();
+  static Register registers[] = { receiver, name, rdx, rbx, rdi, r8 };
   return registers;
 }
 
 
 Register* KeyedLoadStubCompiler::registers() {
   // receiver, name, scratch1, scratch2, scratch3, scratch4.
-  static Register registers[] = { rdx, rax, rbx, rcx, rdi, r8 };
+  Register receiver = KeyedLoadIC::ReceiverRegister();
+  Register name = KeyedLoadIC::NameRegister();
+  static Register registers[] = { receiver, name, rbx, rcx, rdi, r8 };
   return registers;
 }
 
 
 Register StoreStubCompiler::value() {
   return rax;
 }
 
 
 Register* StoreStubCompiler::registers() {
@@ skipping 184 matching lines @@
   // -----------------------------------
   TailCallBuiltin(masm, Builtins::kKeyedLoadIC_Miss);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64