Convert to immutable heap number when materializing arguments object.

src/deoptimizer.cc

Index: src/deoptimizer.cc
diff --git a/src/deoptimizer.cc b/src/deoptimizer.cc
index 7c79c89078b98a74e8d65bfb766e2670a8850ba4..befb0f3b85acf264b312e02ea902f5480903625f 100644
--- a/src/deoptimizer.cc
+++ b/src/deoptimizer.cc
@@ -3389,7 +3389,11 @@ Handle<Object> SlotRefValueBuilder::GetNext(Isolate* isolate, int lvl) {
     case SlotRef::UINT32:
     case SlotRef::DOUBLE:
     case SlotRef::LITERAL: {
-      return slot.GetValue(isolate);
+      Handle<Object> value = slot.GetValue(isolate);
+      if (value->IsMutableHeapNumber()) {

[Igor Sheludko, 2015/02/17 15:07:54]

I think we could save some cycles if we put this code into TAGGED case of
SlotRef::GetValue().

[Jarin, 2015/02/17 15:20:48]

Done. (Even though there is so much stuff going on here that couple of cycles
cannot make any difference.)

+        HeapNumber::cast(*value)->set_map(isolate->heap()->heap_number_map());
+      }
+      return value;
     }
     case SlotRef::ARGUMENTS_OBJECT: {
       // We should never need to materialize an arguments object,