Merge array allocation and List._copyFromObjectArray to provide fast path for large arrays.

runtime/vm/object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 18079 matching lines @@
         Object::Allocate(class_id,
                          Array::InstanceSize(len),
                          space));
     NoGCScope no_gc;
     raw->ptr()->length_ = Smi::New(len);
     return raw;
   }
 }
 
 
+RawArray* Array::Slice(intptr_t start,
+                       intptr_t count,
+                       bool with_type_argument) const {
+  // TODO(vegorov) introduce an array allocation method that fills newly
+  // allocated array with values from the given source array instead of
+  // null-initializing all elements.
+  Array& dest = Array::Handle(Array::New(count));
+  if (dest.raw()->IsNewObject()) {
+    NoGCScope no_gc_scope;
+    memmove(dest.ObjectAddr(0), ObjectAddr(start), count * kWordSize);
+  } else {
+    PassiveObject& obj = PassiveObject::Handle();
+    for (intptr_t i = 0; i < count; i++) {
+      obj = At(start + i);
+      dest.SetAt(i, obj);
+    }
+  }
+
+  if (with_type_argument) {
+    dest.SetTypeArguments(TypeArguments::Handle(GetTypeArguments()));
+  }
+
+  return dest.raw();
+}
+
+
 void Array::MakeImmutable() const {
   NoGCScope no_gc;
   uword tags = raw_ptr()->tags_;
   uword old_tags;
   do {
     old_tags = tags;
     uword new_tags = RawObject::ClassIdTag::update(kImmutableArrayCid,
                                                    old_tags);
     tags = AtomicOperations::CompareAndSwapWord(
         &raw_ptr()->tags_, old_tags, new_tags);
@@ skipping 1510 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart