Encapsulate megamorphic load/tail-call in hydrogen

src/x64/lithium-x64.h

Index: src/x64/lithium-x64.h
diff --git a/src/x64/lithium-x64.h b/src/x64/lithium-x64.h
index a8291473bd31cc8f72a8db698553973093d2c86c..55c599451b406a21c1e9f67536c900026f6d5af5 100644
--- a/src/x64/lithium-x64.h
+++ b/src/x64/lithium-x64.h
@@ -151,6 +151,7 @@ class LCodeGen;
   V(StringCompareAndBranch)                  \
   V(SubI)                                    \
   V(TaggedToI)                               \
+  V(TailCallThroughMegamorphicCache)         \
   V(ThisFunction)                            \
   V(ToFastProperties)                        \
   V(TransitionElementsKind)                  \
@@ -489,6 +490,27 @@ class LCallStub FINAL : public LTemplateInstruction<1, 1, 0> {
 };
 
 
+class LTailCallThroughMegamorphicCache FINAL
+    : public LTemplateInstruction<0, 3, 0> {
+ public:
+  explicit LTailCallThroughMegamorphicCache(LOperand* context,
+                                            LOperand* receiver,
+                                            LOperand* name) {
+    inputs_[0] = context;
+    inputs_[1] = receiver;
+    inputs_[2] = name;
+  }
+
+  LOperand* context() { return inputs_[0]; }
+  LOperand* receiver() { return inputs_[1]; }
+  LOperand* name() { return inputs_[2]; }
+
+  DECLARE_CONCRETE_INSTRUCTION(TailCallThroughMegamorphicCache,
+                               "tail-call-through-megamorphic-cache")
+  DECLARE_HYDROGEN_ACCESSOR(TailCallThroughMegamorphicCache)
+};
+
+
 class LUnknownOSRValue FINAL : public LTemplateInstruction<1, 0, 0> {
  public:
   virtual bool HasInterestingComment(LCodeGen* gen) const OVERRIDE {
@@ -1886,9 +1908,10 @@ class LCallWithDescriptor FINAL : public LTemplateResultInstruction<1> {
 
   LOperand* target() const { return inputs_[0]; }
 
+  DECLARE_HYDROGEN_ACCESSOR(CallWithDescriptor)
+
  private:
   DECLARE_CONCRETE_INSTRUCTION(CallWithDescriptor, "call-with-descriptor")
-  DECLARE_HYDROGEN_ACCESSOR(CallWithDescriptor)
 
   virtual void PrintDataTo(StringStream* stream) OVERRIDE;