Rolled back hash calculation during flattening

src/heap.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1382 matching lines @@
   sliced_string->set_start(start);
   sliced_string->set_length(length);
 
   return result;
 }
 
 
 Object* Heap::AllocateSubString(String* buffer, int start, int end) {
   int length = end - start;
 
+  if (length == 1) {
+    return Heap::LookupSingleCharacterStringFromCode(buffer->Get(start));
+  }
+
   // Make an attempt to flatten the buffer to reduce access time.
   buffer->TryFlatten();
 
   Object* result = buffer->is_ascii()
       ? AllocateRawAsciiString(length)
       : AllocateRawTwoByteString(length);
   if (result->IsFailure()) return result;
 
   // Copy the characters into the new object.
   String* string_result = String::cast(result);
-  for (int i = 0; i < length; i++) {
-    string_result->Set(i, buffer->Get(start + i));
+  StringHasher hasher(length);
+  int i = 0;
+  for (; i < length && hasher.is_array_index(); i++) {
+    uc32 c = buffer->Get(start + i);
+    hasher.AddCharacter(c);
+    string_result->Set(i, c);
   }
+  for (; i < length; i++) {
+    uc32 c = buffer->Get(start + i);
+    hasher.AddCharacterNoIndex(c);
+    string_result->Set(i, c);
+  }
+  string_result->set_length_field(hasher.GetHashField());
   return result;
 }
 
 
 Object* Heap::AllocateExternalStringFromAscii(
     ExternalAsciiString::Resource* resource) {
   Map* map;
   int length = resource->length();
   if (length <= String::kMaxShortStringSize) {
     map = short_external_ascii_string_map();
@@ skipping 1619 matching lines @@
       return "Scavenge";
     case MARK_COMPACTOR:
       return MarkCompactCollector::HasCompacted() ? "Mark-compact"
                                                   : "Mark-sweep";
   }
   return "Unknown GC";
 }
 
 
 } }  // namespace v8::internal