Improve Array.shift() performance for small arrays.

src/x64/lithium-x64.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_X64_LITHIUM_X64_H_
 #define V8_X64_LITHIUM_X64_H_
 
 #include "hydrogen.h"
 #include "lithium-allocator.h"
 #include "lithium.h"
 #include "safepoint-table.h"
 #include "utils.h"
 
 namespace v8 {
 namespace internal {
 
 // Forward declarations.
 class LCodeGen;
 
 #define LITHIUM_CONCRETE_INSTRUCTION_LIST(V)    \
   V(AccessArgumentsAt)                          \
   V(AddI)                                       \
   V(Allocate)                                   \
   V(ApplyArguments)                             \
   V(ArgumentsElements)                          \
   V(ArgumentsLength)                            \
   V(ArithmeticD)                                \
   V(ArithmeticT)                                \
+  V(ArrayShift)                                 \
   V(BitI)                                       \
   V(BoundsCheck)                                \
   V(Branch)                                     \
   V(CallJSFunction)                             \
   V(CallWithDescriptor)                         \
   V(CallFunction)                               \
   V(CallNew)                                    \
   V(CallNewArray)                               \
   V(CallRuntime)                                \
   V(CallStub)                                   \
@@ skipping 2199 matching lines @@
 
   Handle<Map> original_map() { return hydrogen()->original_map().handle(); }
   Handle<Map> transitioned_map() {
     return hydrogen()->transitioned_map().handle();
   }
   ElementsKind from_kind() { return hydrogen()->from_kind(); }
   ElementsKind to_kind() { return hydrogen()->to_kind(); }
 };
 
 
+class LArrayShift V8_FINAL : public LTemplateInstruction<1, 2, 0> {
+ public:
+  LArrayShift(LOperand* context, LOperand* object) {
+    inputs_[0] = context;
+    inputs_[1] = object;
+  }
+
+  LOperand* context() const { return inputs_[0]; }
+  LOperand* object() const { return inputs_[1]; }
+
+  DECLARE_CONCRETE_INSTRUCTION(ArrayShift, "array-shift")
+  DECLARE_HYDROGEN_ACCESSOR(ArrayShift)
+};
+
+
 class LTrapAllocationMemento V8_FINAL : public LTemplateInstruction<0, 1, 1> {
  public:
   LTrapAllocationMemento(LOperand* object,
                          LOperand* temp) {
     inputs_[0] = object;
     temps_[0] = temp;
   }
 
   LOperand* object() { return inputs_[0]; }
   LOperand* temp() { return temps_[0]; }
@@ skipping 552 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(LChunkBuilder);
 };
 
 #undef DECLARE_HYDROGEN_ACCESSOR
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::int
 
 #endif  // V8_X64_LITHIUM_X64_H_