Multiple stubs can point to the same calling convention.

src/ic/x64/ic-conventions-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/codegen.h"
 #include "src/ic/ic-conventions.h"
 
 namespace v8 {
 namespace internal {
 
 // IC register specifications
 const Register LoadConvention::ReceiverRegister() { return rdx; }
 const Register LoadConvention::NameRegister() { return rcx; }
 
 
-const Register VectorLoadConvention::SlotRegister() {
-  DCHECK(FLAG_vector_ics);
-  return rax;
-}
+const Register VectorLoadConvention::SlotRegister() { return rax; }
 
 
-const Register FullVectorLoadConvention::VectorRegister() {
-  DCHECK(FLAG_vector_ics);
-  return rbx;
-}
+const Register FullVectorLoadConvention::VectorRegister() { return rbx; }
 
 
 const Register StoreConvention::ReceiverRegister() { return rdx; }
 const Register StoreConvention::NameRegister() { return rcx; }
 const Register StoreConvention::ValueRegister() { return rax; }
+const Register StoreConvention::MapRegister() { return rbx; }
 
 
-const Register StoreConvention::MapRegister() { return rbx; }
+// Passing arguments in registers is not supported.
+const Register InstanceofConvention::left() { return rax; }
+const Register InstanceofConvention::right() { return rdx; }
 }
 }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64