Implement tracking and optimizations of packed arrays

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 3ba0cae7ad9c4107d6deaf59d9423577516d91ba..fd9574b5db6939c7ab02f6eb4793412f356a1f2d 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -2012,8 +2012,12 @@ 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) ||

[Jakob Kummerow, 2012/05/22 17:36:49]

This computation is used often enough that it would be nice to factor it out
into elements-kind.h:

bool IsSimpleMapChange(ElementsKind from_kind, ElementsKind to_kind) {
  return (GetHoleyElementsKind(from_kind) == to_kind) ||
      (IsFastSmiElementsKind(from_kind) &&
      IsFastObjectElementsKind(to_kind));
}

But then again, this CL is large enough as it is, so feel free to postpone such
cleanup.

[danno, 2012/05/23 14:25:36]

Done.

+      (IsFastSmiElementsKind(from_kind) &&
+       IsFastObjectElementsKind(to_kind));
+  if (simple_map_change) {
     LOperand* object = UseRegister(instr->object());
     LOperand* new_map_reg = TempRegister();
     LOperand* temp_reg = TempRegister();