Improve Array.shift() performance for small arrays.

src/code-stubs.h

Index: src/code-stubs.h
diff --git a/src/code-stubs.h b/src/code-stubs.h
index 8380266d92edf0b13f644f38f3f2917c1fdaf119..b5c07e5a09ef774838257860e10c209060901e42 100644
--- a/src/code-stubs.h
+++ b/src/code-stubs.h
@@ -16,6 +16,7 @@ namespace internal {
 
 // List of code stubs used on all platforms.
 #define CODE_STUB_LIST_ALL_PLATFORMS(V)  \
+  V(ArrayShift)                          \
   V(CallFunction)                        \
   V(CallConstruct)                       \
   V(BinaryOpIC)                          \
@@ -2466,6 +2467,36 @@ class ElementsTransitionAndStoreStub : public HydrogenCodeStub {
 };
 
 
+class ArrayShiftStub V8_FINAL : public HydrogenCodeStub {
+ public:
+  ArrayShiftStub(Isolate* isolate, ElementsKind kind)
+      : HydrogenCodeStub(isolate), kind_(kind) { }
+
+  ElementsKind kind() const { return kind_; }
+
+  virtual Handle<Code> GenerateCode() V8_OVERRIDE;
+
+  virtual void InitializeInterfaceDescriptor(
+      CodeStubInterfaceDescriptor* descriptor) V8_OVERRIDE;
+
+  // Inline Array.shift() for arrays up to this length.
+  static const int kInlineThreshold = 16;
+
+  // Parameters accessed via CodeStubGraphBuilder::GetParameter()
+  static const int kReceiver = 0;
+
+ private:
+  Major MajorKey() { return ArrayShift; }
+  int NotMissMinorKey() {
+    return kind_;
+  }
+
+  ElementsKind kind_;
+
+  DISALLOW_COPY_AND_ASSIGN(ArrayShiftStub);
+};
+
+
 class StoreArrayLiteralElementStub : public PlatformCodeStub {
  public:
   explicit StoreArrayLiteralElementStub(Isolate* isolate)