--- a/src/hotspot/cpu/x86/gc/z/zBarrierSetAssembler_x86.cpp	Tue Jan 29 11:30:17 2019 +0100
+++ b/src/hotspot/cpu/x86/gc/z/zBarrierSetAssembler_x86.cpp	Tue Jan 29 10:23:38 2019 +0100
@@ -279,13 +279,13 @@
   Register ref = stub->ref()->as_register();
   Register ref_addr = noreg;
 
-  if (stub->ref_addr()->is_register()) {
-    // Address already in register
-    ref_addr = stub->ref_addr()->as_pointer_register();
-  } else {
+  if (stub->tmp()->is_valid()) {
     // Load address into tmp register
     ce->leal(stub->ref_addr(), stub->tmp());
     ref_addr = stub->tmp()->as_pointer_register();
+  } else {
+    // Address already in register
+    ref_addr = stub->ref_addr()->as_address_ptr()->base()->as_pointer_register();
   }
 
   assert_different_registers(ref, ref_addr, noreg);

--- a/src/hotspot/share/gc/z/c1/zBarrierSetC1.cpp	Tue Jan 29 11:30:17 2019 +0100
+++ b/src/hotspot/share/gc/z/c1/zBarrierSetC1.cpp	Tue Jan 29 10:23:38 2019 +0100
@@ -38,21 +38,15 @@
     _tmp(LIR_OprFact::illegalOpr),
     _runtime_stub(runtime_stub) {
 
+  assert(_ref_addr->is_address(), "Must be an address");
+  assert(_ref->is_register(), "Must be a register");
+
   // Allocate tmp register if needed
-  if (!_ref_addr->is_register()) {
-    assert(_ref_addr->is_address(), "Must be an address");
-    if (_ref_addr->as_address_ptr()->index()->is_valid() ||
-        _ref_addr->as_address_ptr()->disp() != 0) {
-      // Has index or displacement, need tmp register to load address into
-      _tmp = access.gen()->new_pointer_register();
-    } else {
-      // No index or displacement, address available in base register
-      _ref_addr = _ref_addr->as_address_ptr()->base();
-    }
+  if (_ref_addr->as_address_ptr()->index()->is_valid() ||
+      _ref_addr->as_address_ptr()->disp() != 0) {
+    // Has index or displacement, need tmp register to load address into
+    _tmp = access.gen()->new_pointer_register();
   }
-
-  assert(_ref->is_register(), "Must be a register");
-  assert(_ref_addr->is_register() != _tmp->is_register(), "Only one should be a register");
 }
 
 DecoratorSet ZLoadBarrierStubC1::decorators() const {