Revert "Turn old space cons strings into regular external strings (not short)."

src/objects.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/allocation-site-scopes.h"
 #include "src/api.h"
 #include "src/arguments.h"
@@ skipping 1049 matching lines @@
 #endif  // DEBUG
   Heap* heap = GetHeap();
   int size = this->Size();  // Byte size of the original string.
   if (size < ExternalString::kShortSize) {
     return false;
   }
   bool is_ascii = this->IsOneByteRepresentation();
   bool is_internalized = this->IsInternalizedString();
 
   // Morph the string to an external string by replacing the map and
-  // reinitializing the fields.  This won't work if the space the existing
-  // string occupies is too small for a regular  external string.
-  // Instead, we resort to a short external string instead, omitting
+  // reinitializing the fields.  This won't work if
+  // - the space the existing string occupies is too small for a regular
+  //   external string.
+  // - the existing string is in old pointer space and the backing store of
+  //   the external string is not aligned.  The GC cannot deal with a field
+  //   containing a possibly unaligned address to outside of V8's heap.
+  // In either case we resort to a short external string instead, omitting
   // the field caching the address of the backing store.  When we encounter
   // short external strings in generated code, we need to bailout to runtime.
   Map* new_map;
-  if (size < ExternalString::kSize) {
+  if (size < ExternalString::kSize ||
+      heap->old_pointer_space()->Contains(this)) {
     new_map = is_internalized
         ? (is_ascii
             ? heap->
                 short_external_internalized_string_with_one_byte_data_map()
             : heap->short_external_internalized_string_map())
         : (is_ascii
             ? heap->short_external_string_with_one_byte_data_map()
             : heap->short_external_string_map());
   } else {
     new_map = is_internalized
@@ skipping 40 matching lines @@
   }
 #endif  // DEBUG
   Heap* heap = GetHeap();
   int size = this->Size();  // Byte size of the original string.
   if (size < ExternalString::kShortSize) {
     return false;
   }
   bool is_internalized = this->IsInternalizedString();
 
   // Morph the string to an external string by replacing the map and
-  // reinitializing the fields.  This won't work if the space the existing
-  // string occupies is too small for a regular  external string.
-  // Instead, we resort to a short external string instead, omitting
+  // reinitializing the fields.  This won't work if
+  // - the space the existing string occupies is too small for a regular
+  //   external string.
+  // - the existing string is in old pointer space and the backing store of
+  //   the external string is not aligned.  The GC cannot deal with a field
+  //   containing a possibly unaligned address to outside of V8's heap.
+  // In either case we resort to a short external string instead, omitting
   // the field caching the address of the backing store.  When we encounter
   // short external strings in generated code, we need to bailout to runtime.
   Map* new_map;
-  if (size < ExternalString::kSize) {
+  if (size < ExternalString::kSize ||
+      heap->old_pointer_space()->Contains(this)) {
     new_map = is_internalized
         ? heap->short_external_ascii_internalized_string_map()
         : heap->short_external_ascii_string_map();
   } else {
     new_map = is_internalized
         ? heap->external_ascii_internalized_string_map()
         : heap->external_ascii_string_map();
   }
 
   // Byte size of the external String object.
@@ skipping 15814 matching lines @@
 #define ERROR_MESSAGES_TEXTS(C, T) T,
   static const char* error_messages_[] = {
       ERROR_MESSAGES_LIST(ERROR_MESSAGES_TEXTS)
   };
 #undef ERROR_MESSAGES_TEXTS
   return error_messages_[reason];
 }
 
 
 } }  // namespace v8::internal