Improve Array.shift() performance for small arrays.

src/code-stubs.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_CODE_STUBS_H_
 #define V8_CODE_STUBS_H_
 
 #include "allocation.h"
 #include "assembler.h"
 #include "codegen.h"
 #include "globals.h"
 #include "macro-assembler.h"
 
 namespace v8 {
 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)                          \
   V(BinaryOpICWithAllocationSite)        \
   V(BinaryOpWithAllocationSite)          \
   V(StringAdd)                           \
   V(SubString)                           \
   V(StringCompare)                       \
   V(Compare)                             \
   V(CompareIC)                           \
@@ skipping 2430 matching lines @@
 
   ElementsKind from_kind_;
   ElementsKind to_kind_;
   bool is_jsarray_;
   KeyedAccessStoreMode store_mode_;
 
   DISALLOW_COPY_AND_ASSIGN(ElementsTransitionAndStoreStub);
 };
 
 
+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)
       : PlatformCodeStub(isolate), fp_registers_(CanUseFPRegisters()) { }
 
  private:
   class FPRegisters: public BitField<bool,                0, 1> {};
 
   Major MajorKey() { return StoreArrayLiteralElement; }
   int MinorKey() { return FPRegisters::encode(fp_registers_); }
@@ skipping 59 matching lines @@
 
 
 class CallDescriptors {
  public:
   static void InitializeForIsolate(Isolate* isolate);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_CODE_STUBS_H_