Copy-on-write arrays.

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index 725cbb0c58701d26690626a7514551258055752e..4e89fb6abd87118fe0865bccf81c39086bea473a 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -1330,12 +1330,17 @@ void FullCodeGenerator::VisitArrayLiteral(ArrayLiteral* expr) {
   __ push(FieldOperand(rbx, JSFunction::kLiteralsOffset));
   __ Push(Smi::FromInt(expr->literal_index()));
   __ Push(expr->constant_elements());
-  if (expr->depth() > 1) {
+  if (expr->constant_elements()->map() == Heap::fixed_cow_array_map()) {
+    FastCloneShallowArrayStub stub(
+        FastCloneShallowArrayStub::COPY_ON_WRITE_ELEMENTS, length);
+    __ CallStub(&stub);
+  } else if (expr->depth() > 1) {
     __ CallRuntime(Runtime::kCreateArrayLiteral, 3);
-  } else if (length > FastCloneShallowArrayStub::kMaximumLength) {
+  } else if (length > FastCloneShallowArrayStub::kMaximumClonedLength) {
     __ CallRuntime(Runtime::kCreateArrayLiteralShallow, 3);
   } else {
-    FastCloneShallowArrayStub stub(length);
+    FastCloneShallowArrayStub stub(
+        FastCloneShallowArrayStub::CLONE_ELEMENTS, length);
     __ CallStub(&stub);
   }