X64: Fix bug in boolean conversion of empty string.

src/heap.cc

 // Copyright 2009 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 1651 matching lines @@
   return result;
 }
 
 
 Object* Heap::AllocateSlicedString(String* buffer,
                                    int start,
                                    int end) {
   int length = end - start;
 
   // If the resulting string is small make a sub string.
-  if (end - start <= String::kMinNonFlatLength) {
+  if (length <= String::kMinNonFlatLength) {
     return Heap::AllocateSubString(buffer, start, end);
   }
 
   Map* map;
   if (length <= String::kMaxShortStringSize) {
     map = buffer->IsAsciiRepresentation() ?
       short_sliced_ascii_string_map() :
       short_sliced_string_map();
   } else if (length <= String::kMaxMediumStringSize) {
     map = buffer->IsAsciiRepresentation() ?
@@ skipping 2182 matching lines @@
 #ifdef DEBUG
 bool Heap::GarbageCollectionGreedyCheck() {
   ASSERT(FLAG_gc_greedy);
   if (Bootstrapper::IsActive()) return true;
   if (disallow_allocation_failure()) return true;
   return CollectGarbage(0, NEW_SPACE);
 }
 #endif
 
 } }  // namespace v8::internal