Version 3.7.9.

src/x64/full-codegen-x64.cc

 // Copyright 2011 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 1464 matching lines @@
 
 void FullCodeGenerator::VisitArrayLiteral(ArrayLiteral* expr) {
   Comment cmnt(masm_, "[ ArrayLiteral");
 
   ZoneList<Expression*>* subexprs = expr->values();
   int length = subexprs->length();
   Handle<FixedArray> constant_elements = expr->constant_elements();
   ASSERT_EQ(2, constant_elements->length());
   ElementsKind constant_elements_kind =
       static_cast<ElementsKind>(Smi::cast(constant_elements->get(0))->value());
+  bool has_constant_fast_elements = constant_elements_kind == FAST_ELEMENTS;
   Handle<FixedArrayBase> constant_elements_values(
       FixedArrayBase::cast(constant_elements->get(1)));
 
   __ movq(rbx, Operand(rbp, JavaScriptFrameConstants::kFunctionOffset));
   __ push(FieldOperand(rbx, JSFunction::kLiteralsOffset));
   __ Push(Smi::FromInt(expr->literal_index()));
   __ Push(constant_elements);
-  if (constant_elements_values->map() ==
-      isolate()->heap()->fixed_cow_array_map()) {
+  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);
     FastCloneShallowArrayStub stub(
-        FastCloneShallowArrayStub::COPY_ON_WRITE_ELEMENTS, length);
+        FastCloneShallowArrayStub::COPY_ON_WRITE_ELEMENTS,
+        length);
     __ CallStub(&stub);
-    __ IncrementCounter(isolate()->counters()->cow_arrays_created_stub(), 1);
   } else if (expr->depth() > 1) {
     __ CallRuntime(Runtime::kCreateArrayLiteral, 3);
   } else if (length > FastCloneShallowArrayStub::kMaximumClonedLength) {
     __ CallRuntime(Runtime::kCreateArrayLiteralShallow, 3);
   } else {
     ASSERT(constant_elements_kind == FAST_ELEMENTS ||
            constant_elements_kind == FAST_SMI_ONLY_ELEMENTS ||
            FLAG_smi_only_arrays);
-    FastCloneShallowArrayStub::Mode mode =
-        constant_elements_kind == FAST_DOUBLE_ELEMENTS
-        ? FastCloneShallowArrayStub::CLONE_DOUBLE_ELEMENTS
-        : FastCloneShallowArrayStub::CLONE_ELEMENTS;
+    // If the elements are already FAST_ELEMENTS, the boilerplate cannot
+    // change, so it's possible to specialize the stub in advance.
+    FastCloneShallowArrayStub::Mode mode = has_constant_fast_elements
+        ? FastCloneShallowArrayStub::CLONE_ELEMENTS
+        : FastCloneShallowArrayStub::CLONE_ANY_ELEMENTS;
     FastCloneShallowArrayStub stub(mode, length);
     __ CallStub(&stub);
   }
 
   bool result_saved = false;  // Is the result saved to the stack?
 
   // Emit code to evaluate all the non-constant subexpressions and to store
   // them into the newly cloned array.
   for (int i = 0; i < length; i++) {
     Expression* subexpr = subexprs->at(i);
@@ skipping 2787 matching lines @@
   *context_length = 0;
   return previous_;
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64