Fix slow path of JSON.stringifier when GC strikes.

FlatContent is not GC-safe.

R=verwaest@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/13782002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14175 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/json-stringifier.h

@@ -295,19 +295,30 @@ MaybeObject* BasicJsonStringifier::StringifyString(Isolate* isolate,
     return stringifier.Stringify(object);
   }
 
-  FlattenString(object);
-  String::FlatContent flat = object->GetFlatContent();
-  if (flat.IsAscii()) {
+  object = FlattenGetString(object);
+  ASSERT(object->IsFlat());
+  if (object->IsOneByteRepresentation()) {
+    Handle<String> result =
+        isolate->factory()->NewRawOneByteString(worst_case_length);
+    AssertNoAllocation no_alloc;
+    const uint8_t* start = object->IsSeqOneByteString()
+        ? SeqOneByteString::cast(*object)->GetChars()
+        : ExternalAsciiString::cast(*object)->GetChars();
     return StringifyString_<SeqOneByteString>(
         isolate,
-        flat.ToOneByteVector(),
-        isolate->factory()->NewRawOneByteString(worst_case_length));
+        Vector<const uint8_t>(start, object->length()),
+        result);
   } else {
-    ASSERT(flat.IsTwoByte());
+    Handle<String> result =
+        isolate->factory()->NewRawTwoByteString(worst_case_length);
+    AssertNoAllocation no_alloc;
+    const uc16* start = object->IsSeqTwoByteString()
+        ? SeqTwoByteString::cast(*object)->GetChars()
+        : ExternalTwoByteString::cast(*object)->GetChars();
     return StringifyString_<SeqTwoByteString>(
         isolate,
-        flat.ToUC16Vector(),
-        isolate->factory()->NewRawTwoByteString(worst_case_length));
+        Vector<const uc16>(start, object->length()),
+        result);
   }
 }
 

test/mjsunit/regress/regress-json-stringify-gc.js

@@ -39,3 +39,13 @@ json1 = JSON.stringify(a);
 json2 = JSON.stringify(a);
 assertTrue(json1 == json2, "GC caused JSON.stringify to fail.");
 
+// Check that the slow path of JSON.stringify works correctly wrt GC.
+for (var i = 0; i < 100000; i++) {
+  var s = i.toString();
+  assertEquals('"' + s + '"', JSON.stringify(s, null, 0));
+}
+
+for (var i = 0; i < 100000; i++) {
+  var s = i.toString() + "\u2603";
+  assertEquals('"' + s + '"', JSON.stringify(s, null, 0));
+}