Improve Array.shift() performance for small arrays.

src/hydrogen-instructions.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_HYDROGEN_INSTRUCTIONS_H_
 #define V8_HYDROGEN_INSTRUCTIONS_H_
 
 #include "v8.h"
 
 #include "allocation.h"
@@ skipping 32 matching lines @@
 
 #define HYDROGEN_CONCRETE_INSTRUCTION_LIST(V)  \
   V(AbnormalExit)                              \
   V(AccessArgumentsAt)                         \
   V(Add)                                       \
   V(Allocate)                                  \
   V(ApplyArguments)                            \
   V(ArgumentsElements)                         \
   V(ArgumentsLength)                           \
   V(ArgumentsObject)                           \
+  V(ArrayShift)                                \
   V(Bitwise)                                   \
   V(BlockEntry)                                \
   V(BoundsCheck)                               \
   V(BoundsCheckBaseIndexInformation)           \
   V(Branch)                                    \
   V(CallWithDescriptor)                        \
   V(CallJSFunction)                            \
   V(CallFunction)                              \
   V(CallNew)                                   \
   V(CallNewArray)                              \
@@ skipping 7007 matching lines @@
     set_representation(Representation::Tagged());
   }
 
   Unique<Map> original_map_;
   Unique<Map> transitioned_map_;
   ElementsKind from_kind_;
   ElementsKind to_kind_;
 };
 
 
+class HArrayShift V8_FINAL : public HTemplateInstruction<2> {
+ public:
+  static HArrayShift* New(Zone* zone,
+                          HValue* context,
+                          HValue* object,
+                          ElementsKind kind) {
+    return new(zone) HArrayShift(context, object, kind);
+  }
+
+  virtual Representation RequiredInputRepresentation(int index) V8_OVERRIDE {
+    return Representation::Tagged();
+  }
+
+  HValue* context() const { return OperandAt(0); }
+  HValue* object() const { return OperandAt(1); }
+  ElementsKind kind() const { return kind_; }
+
+  virtual void PrintDataTo(StringStream* stream) V8_OVERRIDE;
+
+  DECLARE_CONCRETE_INSTRUCTION(ArrayShift);
+
+ protected:
+  virtual bool DataEquals(HValue* other) V8_OVERRIDE {
+    HArrayShift* that = HArrayShift::cast(other);
+    return this->kind_ == that->kind_;
+  }
+
+ private:
+  HArrayShift(HValue* context, HValue* object, ElementsKind kind)
+      : kind_(kind) {
+    SetOperandAt(0, context);
+    SetOperandAt(1, object);
+    SetChangesFlag(kNewSpacePromotion);
+    set_representation(Representation::Tagged());
+    if (IsFastSmiOrObjectElementsKind(kind)) {
+      SetChangesFlag(kArrayElements);
+    } else {
+      SetChangesFlag(kDoubleArrayElements);
+    }
+  }
+
+  ElementsKind kind_;
+};
+
+
 class HStringAdd V8_FINAL : public HBinaryOperation {
  public:
   static HInstruction* New(Zone* zone,
                            HValue* context,
                            HValue* left,
                            HValue* right,
                            PretenureFlag pretenure_flag = NOT_TENURED,
                            StringAddFlags flags = STRING_ADD_CHECK_BOTH,
                            Handle<AllocationSite> allocation_site =
                                Handle<AllocationSite>::null());
@@ skipping 561 matching lines @@
   virtual bool IsDeletable() const V8_OVERRIDE { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_