Correctly handle holes when concat()ing double arrays

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 10523 matching lines @@
 
   // If estimated number of elements is more than half of length, a
   // fixed array (fast case) is more time and space-efficient than a
   // dictionary.
   bool fast_case = (estimate_nof_elements * 2) >= estimate_result_length;
 
   if (fast_case && kind == FAST_DOUBLE_ELEMENTS) {
     Handle<FixedArrayBase> storage =
         isolate->factory()->NewFixedDoubleArray(estimate_result_length);
     int j = 0;
+    bool failure = false;
     if (estimate_result_length > 0) {
       Handle<FixedDoubleArray> double_storage =
           Handle<FixedDoubleArray>::cast(storage);
-      bool failure = false;
       for (int i = 0; i < argument_count; i++) {
         Handle<Object> obj(elements->get(i), isolate);
         if (obj->IsSmi()) {
           double_storage->set(j, Smi::cast(*obj)->value());
           j++;
         } else if (obj->IsNumber()) {
           double_storage->set(j, obj->Number());
           j++;
         } else {
           JSArray* array = JSArray::cast(*obj);
           uint32_t length = static_cast<uint32_t>(array->length()->Number());
           switch (array->map()->elements_kind()) {
             case FAST_HOLEY_DOUBLE_ELEMENTS:
             case FAST_DOUBLE_ELEMENTS: {
               // Empty array is FixedArray but not FixedDoubleArray.
               if (length == 0) break;
               FixedDoubleArray* elements =
                   FixedDoubleArray::cast(array->elements());
               for (uint32_t i = 0; i < length; i++) {
                 if (elements->is_the_hole(i)) {
+                  // TODO(jkummerow/verwaest): We could be a bit more clever
+                  // here: Check if there are no elements/getters on the
+                  // prototype chain, and if so, allow creation of a holey
+                  // result array.
+                  // Same thing below (holey smi case).
                   failure = true;
                   break;
                 }
                 double double_value = elements->get_scalar(i);
                 double_storage->set(j, double_value);
                 j++;
               }
               break;
             }
             case FAST_HOLEY_SMI_ELEMENTS:
             case FAST_SMI_ELEMENTS: {
               FixedArray* elements(
                   FixedArray::cast(array->elements()));
               for (uint32_t i = 0; i < length; i++) {
                 Object* element = elements->get(i);
                 if (element->IsTheHole()) {
                   failure = true;
                   break;
                 }
                 int32_t int_value = Smi::cast(element)->value();
                 double_storage->set(j, int_value);
                 j++;
               }
               break;
             }
             case FAST_HOLEY_ELEMENTS:
+            case FAST_ELEMENTS:
               DCHECK_EQ(0, length);
               break;
             default:
               UNREACHABLE();
           }
         }
         if (failure) break;
       }
     }
-    Handle<JSArray> array = isolate->factory()->NewJSArray(0);
-    Smi* length = Smi::FromInt(j);
-    Handle<Map> map;
-    map = JSObject::GetElementsTransitionMap(array, kind);
-    array->set_map(*map);
-    array->set_length(length);
-    array->set_elements(*storage);
-    return *array;
+    if (!failure) {
+      Handle<JSArray> array = isolate->factory()->NewJSArray(0);
+      Smi* length = Smi::FromInt(j);
+      Handle<Map> map;
+      map = JSObject::GetElementsTransitionMap(array, kind);
+      array->set_map(*map);
+      array->set_length(length);
+      array->set_elements(*storage);
+      return *array;
+    }
+    // In case of failure, fall through.
   }
 
   Handle<FixedArray> storage;
   if (fast_case) {
     // The backing storage array must have non-existing elements to preserve
     // holes across concat operations.
     storage = isolate->factory()->NewFixedArrayWithHoles(
         estimate_result_length);
   } else {
     // TODO(126): move 25% pre-allocation logic into Dictionary::Allocate
@@ skipping 5009 matching lines @@
   }
   return NULL;
 }
 
 
 const Runtime::Function* Runtime::FunctionForId(Runtime::FunctionId id) {
   return &(kIntrinsicFunctions[static_cast<int>(id)]);
 }
 
 } }  // namespace v8::internal