Convert to immutable heap number when materializing arguments object.

src/deoptimizer.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
 #include "src/codegen.h"
 #include "src/deoptimizer.h"
 #include "src/disasm.h"
@@ skipping 3371 matching lines @@
 
 Handle<Object> SlotRefValueBuilder::GetNext(Isolate* isolate, int lvl) {
   SlotRef& slot = slot_refs_[current_slot_];
   current_slot_++;
   switch (slot.Representation()) {
     case SlotRef::TAGGED:
     case SlotRef::INT32:
     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,
       // but we still need to put something into the array
       // so that the indexing is consistent.
       materialized_objects_.Add(isolate->factory()->undefined_value());
       int length = slot.GetChildrenCount();
       for (int i = 0; i < length; ++i) {
         // We don't need the argument, just ignore it
         GetNext(isolate, lvl + 1);
@@ skipping 260 matching lines @@
            Deoptimizer::GetDeoptimizationId(isolate, info->target_address(),
                                             Deoptimizer::LAZY))) {
         CHECK(RelocInfo::IsRuntimeEntry(info->rmode()));
         return DeoptInfo(last_position, NULL, last_reason);
       }
     }
   }
   return DeoptInfo(0, NULL, Deoptimizer::kNoReason);
 }
 } }  // namespace v8::internal