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

This reverts commits r22192 and r22194.

TBR=hpayer@chromium.org

Review URL: https://codereview.chromium.org/367113003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22195 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap-inl.h

@@ -470,7 +470,8 @@ bool Heap::AllowedToBeMigrated(HeapObject* obj, AllocationSpace dst) {
       return dst == src || dst == TargetSpaceId(type);
     case OLD_POINTER_SPACE:
       return dst == src && (dst == TargetSpaceId(type) || obj->IsFiller() ||
-                            (obj->IsExternalString()));
+                            (obj->IsExternalString() &&
+                             ExternalString::cast(obj)->is_short()));
     case OLD_DATA_SPACE:
       return dst == src && dst == TargetSpaceId(type);
     case CODE_SPACE:

src/objects.cc

@@ -1067,13 +1067,18 @@ bool String::MakeExternal(v8::String::ExternalStringResource* resource) {
   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->
@@ -1134,13 +1139,18 @@ bool String::MakeExternal(v8::String::ExternalAsciiStringResource* resource) {
   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();

test/mjsunit/regress/regress-sliced-external-cons-regexp.js

-// Copyright 2014 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.
-
-// Flags: --expose-externalize-string --expose-gc
-
-var re = /(B)/;
-var cons1 = "0123456789" + "ABCDEFGHIJ";
-var cons2 = "0123456789\u1234" + "ABCDEFGHIJ";
-gc();
-gc();  // Promote cons.
-
-try { externalizeString(cons1, false); } catch (e) { }
-try { externalizeString(cons2, true); } catch (e) { }
-
-var slice1 = cons1.slice(1,-1);
-var slice2 = cons2.slice(1,-1);
-for (var i = 0; i < 10; i++) {
-  assertEquals(["B", "B"], re.exec(slice1));
-  assertEquals(["B", "B"], re.exec(slice2));
-}