Use Copy-on-write arrays for cached regexp results.

src/runtime.cc

 // Copyright 2006-2009 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 1346 matching lines @@
   array->set_properties(Heap::empty_fixed_array());
   array->set_elements(elements);
   array->set_length(Smi::FromInt(elements_count));
   // Write in-object properties after the length of the array.
   array->InObjectPropertyAtPut(JSRegExpResult::kIndexIndex, args[1]);
   array->InObjectPropertyAtPut(JSRegExpResult::kInputIndex, args[2]);
   return array;
 }
 
 
+static Object* Runtime_RegExpCloneResult(Arguments args) {
+  ASSERT(args.length() == 1);
+  Map* regexp_result_map;
+  {
+    AssertNoAllocation no_gc;
+    HandleScope handles;
+    regexp_result_map = Top::global_context()->regexp_result_map();
+  }
+  if (!args[0]->IsJSArray()) return args[0];
+
+  JSArray* result = JSArray::cast(args[0]);
+  // Arguments to RegExpCloneResult should always be fresh RegExp exec call
+  // results (either a fresh JSRegExpResult or null).
+  // If the argument is not a JSRegExpResult, or isn't unmodified, just return
+  // the argument uncloned.
+  if (result->map() != regexp_result_map) return result;
+
+  // Having the original JSRegExpResult map guarantees that we have
+  // fast elements and no properties except the two in-object properties.
+  ASSERT(result->HasFastElements());
+  ASSERT(result->properties() == Heap::empty_fixed_array());
+  ASSERT_EQ(2, regexp_result_map->inobject_properties());
+
+  Object* new_array_alloc = Heap::AllocateRaw(JSRegExpResult::kSize,
+                                              NEW_SPACE,
+                                              OLD_POINTER_SPACE);
+  if (new_array_alloc->IsFailure()) return new_array_alloc;
+
+  // Set HeapObject map to JSRegExpResult map.
+  reinterpret_cast<HeapObject*>(new_array_alloc)->set_map(regexp_result_map);
+
+  JSArray* new_array = JSArray::cast(new_array_alloc);
+
+  // Copy JSObject properties.
+  new_array->set_properties(result->properties());  // Empty FixedArray.
+
+  // Copy JSObject elements as copy-on-write.
+  FixedArray* elements = FixedArray::cast(result->elements());
+  if (elements != Heap::empty_fixed_array()) {
+    ASSERT(!Heap::InNewSpace(Heap::fixed_cow_array_map()));
+    // No write barrier is necessary when writing old-space pointer.

[Vitaly Repeshko, 2010/08/20 13:29:49]

I don't think we need to have this comment or assert for map assignment.

[Lasse Reichstein, 2010/08/23 12:52:11]

True, maps are all in Map-space.

+    elements->set_map(Heap::fixed_cow_array_map());
+  }
+  new_array->set_elements(elements);
+
+  // Copy JSArray length.
+  new_array->set_length(result->length());
+
+  // Copy JSRegExpResult in-object property fields input and index.
+  new_array->FastPropertyAtPut(JSRegExpResult::kIndexIndex,
+                               result->FastPropertyAt(
+                                   JSRegExpResult::kIndexIndex));
+  new_array->FastPropertyAtPut(JSRegExpResult::kInputIndex,
+                               result->FastPropertyAt(
+                                   JSRegExpResult::kInputIndex));
+  return new_array;
+}
+
+
 static Object* Runtime_RegExpInitializeObject(Arguments args) {
   AssertNoAllocation no_alloc;
   ASSERT(args.length() == 5);
   CONVERT_CHECKED(JSRegExp, regexp, args[0]);
   CONVERT_CHECKED(String, source, args[1]);
 
   Object* global = args[2];
   if (!global->IsTrue()) global = Heap::false_value();
 
   Object* ignoreCase = args[3];
@@ skipping 9273 matching lines @@
   } else {
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     Counters::gc_last_resort_from_js.Increment();
     Heap::CollectAllGarbage(false);
   }
 }
 
 
 } }  // namespace v8::internal