Array.concat: properly go to dictionary mode when required

src/runtime.cc

 // Copyright 2012 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 <stdlib.h>
 #include <limits>
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
@@ skipping 10022 matching lines @@
 
     if (fast_elements_) {
       if (index < static_cast<uint32_t>(storage_->length())) {
         storage_->set(index, *elm);
         return;
       }
       // Our initial estimate of length was foiled, possibly by
       // getters on the arrays increasing the length of later arrays
       // during iteration.
       // This shouldn't happen in anything but pathological cases.
-      SetDictionaryMode(index);
+      SetDictionaryMode();
       // Fall-through to dictionary mode.
     }
     ASSERT(!fast_elements_);
     Handle<SeededNumberDictionary> dict(
         SeededNumberDictionary::cast(*storage_));
     Handle<SeededNumberDictionary> result =
         SeededNumberDictionary::AtNumberPut(dict, index, elm);
     if (!result.is_identical_to(dict)) {
       // Dictionary needed to grow.
       clear_storage();
       set_storage(*result);
     }
   }
 
   void increase_index_offset(uint32_t delta) {
     if (JSObject::kMaxElementCount - index_offset_ < delta) {
       index_offset_ = JSObject::kMaxElementCount;
     } else {
       index_offset_ += delta;
     }
+    // If the initial length estimate was off (see special case in visit()),
+    // but the array blowing the limit didn't contain elements beyond the
+    // provided-for index range, go to dictionary mode now.
+    if (fast_elements_ &&
+        index_offset_ >= static_cast<uint32_t>(
+            FixedArrayBase::cast(*storage_)->length())) {
+      SetDictionaryMode();
+    }
   }
 
   bool exceeds_array_limit() {
     return exceeds_array_limit_;
   }
 
   Handle<JSArray> ToArray() {
     Handle<JSArray> array = isolate_->factory()->NewJSArray(0);
     Handle<Object> length =
         isolate_->factory()->NewNumber(static_cast<double>(index_offset_));
     Handle<Map> map = JSObject::GetElementsTransitionMap(
         array,
         fast_elements_ ? FAST_HOLEY_ELEMENTS : DICTIONARY_ELEMENTS);
     array->set_map(*map);
     array->set_length(*length);
     array->set_elements(*storage_);
     return array;
   }
 
  private:
   // Convert storage to dictionary mode.
-  void SetDictionaryMode(uint32_t index) {
+  void SetDictionaryMode() {
     ASSERT(fast_elements_);
     Handle<FixedArray> current_storage(*storage_);
     Handle<SeededNumberDictionary> slow_storage(
         SeededNumberDictionary::New(isolate_, current_storage->length()));
     uint32_t current_length = static_cast<uint32_t>(current_storage->length());
     for (uint32_t i = 0; i < current_length; i++) {
       HandleScope loop_scope(isolate_);
       Handle<Object> element(current_storage->get(i), isolate_);
       if (!element->IsTheHole()) {
         Handle<SeededNumberDictionary> new_storage =
@@ skipping 5123 matching lines @@
   }
   return NULL;
 }
 
 
 const Runtime::Function* Runtime::FunctionForId(Runtime::FunctionId id) {
   return &(kIntrinsicFunctions[static_cast<int>(id)]);
 }
 
 } }  // namespace v8::internal