Implement local check elimination on basic blocks.

src/unique.h

Index: src/unique.h
diff --git a/src/unique.h b/src/unique.h
index fdb7016d799376f5dd390a1a2a4ca5f6f6ce768f..a93b04699350dddc4aa9de528eba9abfbd199177 100644
--- a/src/unique.h
+++ b/src/unique.h
@@ -120,6 +120,10 @@ class Unique V8_FINAL {
     return handle_;
   }
 
+  template <class S> static Unique<T> cast(Unique<S> that) {
+    return Unique<T>(that.raw_address_, Handle<T>::cast(that.handle_));
+  }
+
   inline bool IsInitialized() const {
     return raw_address_ != NULL || handle_.is_null();
   }
@@ -169,6 +173,17 @@ class UniqueSet V8_FINAL : public ZoneObject {
     array_[size_++] = uniq;
   }
 
+  // Remove an element from this set. Mutates this set. O(|this|)
+  void Remove(Unique<T> uniq) {
+    for (int i = 0; i < size_; i++) {
+      if (array_[i] == uniq) {
+        while (++i < size_) array_[i - 1] = array_[i];
+        size_--;
+        return;
+      }
+    }
+  }
+
   // Compare this set against another set. O(|this|).
   bool Equals(UniqueSet<T>* that) const {
     if (that->size_ != this->size_) return false;
@@ -273,6 +288,10 @@ class UniqueSet V8_FINAL : public ZoneObject {
     return copy;
   }
 
+  void Clear() {
+    size_ = 0;
+  }
+
   inline int size() const {
     return size_;
   }