[turbofan] Revive the VectorSlotPair and also put feedback on JSCallFunction.

src/handles.h

 // Copyright 2011 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_HANDLES_H_
 #define V8_HANDLES_H_
 
 #include "src/objects.h"
 
 namespace v8 {
@@ skipping 48 matching lines @@
       *out = Handle<T>::null();
       return false;
     } else {
       *out = Handle<T>(location_);
       return true;
     }
   }
 
   bool is_null() const { return location_ == NULL; }
 
+  template <typename S>
+  bool operator==(MaybeHandle<S> that) const {
+    return this->location_ == that.location_;
+  }
+  template <typename S>
+  bool operator!=(MaybeHandle<S> that) const {
+    return !(*this == that);
+  }
+
+
  protected:
   T** location_;
 
   // MaybeHandles of different classes are allowed to access each
   // other's location_.
   template<class S> friend class MaybeHandle;
+  template <typename S>
+  friend size_t hash_value(MaybeHandle<S>);
 };
 
+template <typename S>
+inline size_t hash_value(MaybeHandle<S> maybe_handle) {
+  return bit_cast<size_t>(maybe_handle.location_);
+}
+
+
 // ----------------------------------------------------------------------------
 // A Handle provides a reference to an object that survives relocation by
 // the garbage collector.
 // Handles are only valid within a HandleScope.
 // When a handle is created for an object a cell is allocated in the heap.
 
 template<typename T>
 class Handle {
  public:
   INLINE(explicit Handle(T** location)) { location_ = location; }
@@ skipping 202 matching lines @@
 
   void Initialize() {
     next = limit = NULL;
     level = 0;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_HANDLES_H_