Multiple stubs can point to the same calling convention.

src/ic/x64/ic-conventions-x64.cc

Index: src/ic/x64/ic-conventions-x64.cc
diff --git a/src/ic/x64/ic-conventions-x64.cc b/src/ic/x64/ic-conventions-x64.cc
index cd19f3fe3927241a348cb78bb7fd9bd4e3ab30d4..0873da53c3d3919b33c4af5bc19a62add101208f 100644
--- a/src/ic/x64/ic-conventions-x64.cc
+++ b/src/ic/x64/ic-conventions-x64.cc
@@ -17,24 +17,21 @@ 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