Revert "Refactor transitioning stores."

src/arm/lithium-arm.cc

Index: src/arm/lithium-arm.cc
diff --git a/src/arm/lithium-arm.cc b/src/arm/lithium-arm.cc
index 714c12a3fb2e3bd5956282663f49a994dd21624e..7a4de9f4ccad29a23d8605c4738d86492276bb96 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -2279,6 +2279,8 @@ LInstruction* LChunkBuilder::DoTrapAllocationMemento(
 LInstruction* LChunkBuilder::DoStoreNamedField(HStoreNamedField* instr) {
   bool is_in_object = instr->access().IsInobject();
   bool needs_write_barrier = instr->NeedsWriteBarrier();
+  bool needs_write_barrier_for_map = instr->has_transition() &&
+      instr->NeedsWriteBarrierForMap();
 
   LOperand* obj;
   if (needs_write_barrier) {
@@ -2286,7 +2288,9 @@ LInstruction* LChunkBuilder::DoStoreNamedField(HStoreNamedField* instr) {
         ? UseRegister(instr->object())
         : UseTempRegister(instr->object());
   } else {
-    obj = UseRegisterAtStart(instr->object());
+    obj = needs_write_barrier_for_map
+        ? UseRegister(instr->object())
+        : UseRegisterAtStart(instr->object());
   }
 
   LOperand* val;
@@ -2298,7 +2302,10 @@ LInstruction* LChunkBuilder::DoStoreNamedField(HStoreNamedField* instr) {
     val = UseRegister(instr->value());
   }
 
-  LInstruction* result = new(zone()) LStoreNamedField(obj, val);
+  // We need a temporary register for write barrier of the map field.
+  LOperand* temp = needs_write_barrier_for_map ? TempRegister() : NULL;
+
+  LInstruction* result = new(zone()) LStoreNamedField(obj, val, temp);
   if (!instr->access().IsExternalMemory() &&
       instr->field_representation().IsHeapObject() &&
       !instr->value()->type().IsHeapObject()) {