Implement tracking and optimizations of packed arrays

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 5c60f5321c19d787f6f5b10351ec3d06a2c69a89..dd54f11ea975862cfc7c1e54ca966693c8fdb966 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -2082,8 +2082,12 @@ LInstruction* LChunkBuilder::DoStoreKeyedGeneric(HStoreKeyedGeneric* instr) {
 
 LInstruction* LChunkBuilder::DoTransitionElementsKind(
     HTransitionElementsKind* instr) {
-  if (instr->original_map()->elements_kind() == FAST_SMI_ONLY_ELEMENTS &&
-      instr->transitioned_map()->elements_kind() == FAST_ELEMENTS) {
+  ElementsKind from_kind = instr->original_map()->elements_kind();
+  ElementsKind to_kind = instr->transitioned_map()->elements_kind();
+  bool simple_map_change = (GetHoleyElementsKind(from_kind) == to_kind) ||
+      (IsFastSmiElementsKind(from_kind) &&
+       IsFastObjectElementsKind(to_kind));
+  if (simple_map_change) {
     LOperand* object = UseRegister(instr->object());
     LOperand* new_map_reg = TempRegister();
     LTransitionElementsKind* result =