Cache lookups at megamorphic call sites in optimized code.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 2b43f970ddbf794d8eccee97cd33a6ddcfac9262..22754f86234dd13eaed0061f33457159d447dac5 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -294,6 +294,9 @@ class Object {
   }
   static RawClass* unwind_error_class() { return unwind_error_class_; }
   static RawClass* icdata_class() { return icdata_class_; }
+  static RawClass* megamorphic_cache_class() {
+    return megamorphic_cache_class_;
+  }
   static RawClass* subtypetestcache_class() { return subtypetestcache_class_; }
 
   static RawError* Init(Isolate* isolate);
@@ -428,6 +431,7 @@ class Object {
   static RawClass* context_class_;  // Class of the Context vm object.
   static RawClass* context_scope_class_;  // Class of ContextScope vm object.
   static RawClass* icdata_class_;  // Class of ICData.
+  static RawClass* megamorphic_cache_class_;  // Class of MegamorphiCache.
   static RawClass* subtypetestcache_class_;  // Class of SubtypeTestCache.
   static RawClass* api_error_class_;  // Class of ApiError.
   static RawClass* language_error_class_;  // Class of LanguageError.
@@ -2926,6 +2930,44 @@ class ICData : public Object {
 };
 
 
+class MegamorphicCache : public Object {
+ public:
+  static const int kInitialCapacity = 16;
+  static const double kLoadFactor = 0.75;
+
+  RawArray* buckets() const;
+  void set_buckets(const Array& buckets) const;
+
+  intptr_t mask() const;
+  void set_mask(intptr_t mask) const;
+
+  intptr_t fill_count() const;
+  void set_fill_count(intptr_t fill_count) const;
+
+  static intptr_t buckets_offset() {
+    return OFFSET_OF(RawMegamorphicCache, buckets_);
+  }
+  static intptr_t mask_offset() {
+    return OFFSET_OF(RawMegamorphicCache, mask_);
+  }
+
+  static RawMegamorphicCache* New();
+
+  void EnsureCapacity() const;
+
+  void Insert(const Smi& class_id, const Function& target) const;
+
+  static intptr_t InstanceSize() {
+    return RoundedAllocationSize(sizeof(RawMegamorphicCache));
+  }
+
+ private:
+  friend class Class;
+
+  HEAP_OBJECT_IMPLEMENTATION(MegamorphicCache, Object);
+};
+
+
 class SubtypeTestCache : public Object {
  public:
   enum Entries {