Revert "Refactor transitioning stores."

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index d10b4364a1e46c901a2f8c8b94ea816f4854f47e..cbade8a7d95fac4b2309b7e1fd648a3f17ba1454 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -2276,6 +2276,8 @@ LInstruction* LChunkBuilder::DoStoreNamedField(HStoreNamedField* instr) {
   bool is_external_location = instr->access().IsExternalMemory() &&
       instr->access().offset() == 0;
   bool needs_write_barrier = instr->NeedsWriteBarrier();
+  bool needs_write_barrier_for_map = instr->has_transition() &&
+      instr->NeedsWriteBarrierForMap();
 
   LOperand* obj;
   if (needs_write_barrier) {
@@ -2285,9 +2287,12 @@ LInstruction* LChunkBuilder::DoStoreNamedField(HStoreNamedField* instr) {
   } else if (is_external_location) {
     ASSERT(!is_in_object);
     ASSERT(!needs_write_barrier);
+    ASSERT(!needs_write_barrier_for_map);
     obj = UseRegisterOrConstant(instr->object());
   } else {
-    obj = UseRegisterAtStart(instr->object());
+    obj = needs_write_barrier_for_map
+        ? UseRegister(instr->object())
+        : UseRegisterAtStart(instr->object());
   }
 
   bool can_be_constant = instr->value()->IsConstant() &&
@@ -2311,8 +2316,8 @@ LInstruction* LChunkBuilder::DoStoreNamedField(HStoreNamedField* instr) {
 
   // We only need a scratch register if we have a write barrier or we
   // have a store into the properties array (not in-object-property).
-  LOperand* temp = (!is_in_object || needs_write_barrier)
-      ? TempRegister() : NULL;
+  LOperand* temp = (!is_in_object || needs_write_barrier ||
+      needs_write_barrier_for_map) ? TempRegister() : NULL;
 
   LInstruction* result = new(zone()) LStoreNamedField(obj, val, temp);
   if (!instr->access().IsExternalMemory() &&