Object pool with support for untagged entries.

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
diff --git a/runtime/vm/raw_object.h b/runtime/vm/raw_object.h
index 349ad591e30cc73ac2bb7b5209ce0db66c02d8c0..f4b80b336f162ba78d1223c7868d99e744fec58d 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -31,6 +31,7 @@ namespace dart {
   V(Namespace)                                                                 \
   V(Code)                                                                      \
   V(Instructions)                                                              \
+  V(ObjectPool)                                                                \
   V(PcDescriptors)                                                             \
   V(Stackmap)                                                                  \
   V(LocalVarDescriptors)                                                       \
@@ -1002,6 +1003,27 @@ class RawCode : public RawObject {
 };
 
 
+class RawObjectPool : public RawObject {
+  RAW_HEAP_OBJECT_IMPLEMENTATION(ObjectPool);
+
+  intptr_t length_;
+  RawTypedData* info_array_;
+
+  struct Entry {
+    union {
+      RawObject* raw_obj_;
+      uword raw_value_;
+    };
+  };
+  Entry* data() { OPEN_ARRAY_START(Entry, Entry); }
+  Entry const* data() const { OPEN_ARRAY_START(Entry, Entry); }
+
+  Entry* first_entry() { return &ptr()->data()[0]; }
+
+  friend class Object;
+};
+
+
 class RawInstructions : public RawObject {
   RAW_HEAP_OBJECT_IMPLEMENTATION(Instructions);
 
@@ -1009,7 +1031,7 @@ class RawInstructions : public RawObject {
     return reinterpret_cast<RawObject**>(&ptr()->code_);
   }
   RawCode* code_;
-  RawArray* object_pool_;
+  RawObjectPool* object_pool_;
   RawObject** to() {
     return reinterpret_cast<RawObject**>(&ptr()->object_pool_);
   }
@@ -1780,6 +1802,8 @@ class RawTypedData : public RawInstance {
   friend class Object;
   friend class Instance;
   friend class SnapshotReader;
+  friend class ObjectPool;
+  friend class RawObjectPool;
 };
 
 
@@ -2112,6 +2136,7 @@ inline bool RawObject::IsVariableSizeClassId(intptr_t index) {
          (index == kContextCid) ||
          (index == kTypeArgumentsCid) ||
          (index == kInstructionsCid) ||
+         (index == kObjectPoolCid) ||
          (index == kPcDescriptorsCid) ||
          (index == kStackmapCid) ||
          (index == kLocalVarDescriptorsCid) ||