Revert r20974: Unify and simplify the FastCloneShallowArrayStub

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 d974033fd832e3bb0de58c65d00d8bd0ca0760c1..ae72ba7ad68102a6019610a843992107e654129e 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -1796,7 +1796,24 @@ void FullCodeGenerator::VisitArrayLiteral(ArrayLiteral* expr) {
     allocation_site_mode = DONT_TRACK_ALLOCATION_SITE;
   }
 
-  if (expr->depth() > 1) {
+  Heap* heap = isolate()->heap();
+  if (has_constant_fast_elements &&
+      constant_elements_values->map() == heap->fixed_cow_array_map()) {
+    // If the elements are already FAST_*_ELEMENTS, the boilerplate cannot
+    // change, so it's possible to specialize the stub in advance.
+    __ IncrementCounter(isolate()->counters()->cow_arrays_created_stub(), 1);
+    __ movp(rbx, Operand(rbp, JavaScriptFrameConstants::kFunctionOffset));
+    __ movp(rax, FieldOperand(rbx, JSFunction::kLiteralsOffset));
+    __ Move(rbx, Smi::FromInt(expr->literal_index()));
+    __ Move(rcx, constant_elements);
+    FastCloneShallowArrayStub stub(
+        isolate(),
+        FastCloneShallowArrayStub::COPY_ON_WRITE_ELEMENTS,
+        allocation_site_mode,
+        length);
+    __ CallStub(&stub);
+  } else if (expr->depth() > 1 || Serializer::enabled() ||
+             length > FastCloneShallowArrayStub::kMaximumClonedLength) {
     __ movp(rbx, Operand(rbp, JavaScriptFrameConstants::kFunctionOffset));
     __ Push(FieldOperand(rbx, JSFunction::kLiteralsOffset));
     __ Push(Smi::FromInt(expr->literal_index()));
@@ -1804,11 +1821,24 @@ void FullCodeGenerator::VisitArrayLiteral(ArrayLiteral* expr) {
     __ Push(Smi::FromInt(flags));
     __ CallRuntime(Runtime::kHiddenCreateArrayLiteral, 4);
   } else {
+    ASSERT(IsFastSmiOrObjectElementsKind(constant_elements_kind) ||
+           FLAG_smi_only_arrays);
+    FastCloneShallowArrayStub::Mode mode =
+        FastCloneShallowArrayStub::CLONE_ANY_ELEMENTS;
+
+    // If the elements are already FAST_*_ELEMENTS, the boilerplate cannot
+    // change, so it's possible to specialize the stub in advance.
+    if (has_constant_fast_elements) {
+      mode = FastCloneShallowArrayStub::CLONE_ELEMENTS;
+    }
+
     __ movp(rbx, Operand(rbp, JavaScriptFrameConstants::kFunctionOffset));
     __ movp(rax, FieldOperand(rbx, JSFunction::kLiteralsOffset));
     __ Move(rbx, Smi::FromInt(expr->literal_index()));
     __ Move(rcx, constant_elements);
-    FastCloneShallowArrayStub stub(isolate(), allocation_site_mode);
+    FastCloneShallowArrayStub stub(isolate(),
+                                   mode,
+                                   allocation_site_mode, length);
     __ CallStub(&stub);
   }