Re-landing of "replace TrySync with Metadata".

runtime/vm/exceptions.h

Index: runtime/vm/exceptions.h
diff --git a/runtime/vm/exceptions.h b/runtime/vm/exceptions.h
index c2a3350042b24ec8941869ff52528da1d6f4e385..9debccee01d943307ec70400400afba6e86e586b 100644
--- a/runtime/vm/exceptions.h
+++ b/runtime/vm/exceptions.h
@@ -102,6 +102,65 @@ struct ExceptionHandlerInfo {
   int8_t is_generated;         // True if this is a generated handler.
 };
 
+
+class CatchEntryState {
+ public:
+  enum { kCatchEntryStateIsMove = 1, kCatchEntryStateDestShift = 1 };
+
+  CatchEntryState() : data_(NULL), ref_count_(NULL) {}
+  explicit CatchEntryState(intptr_t* data)
+      : data_(data), ref_count_(new intptr_t(1)) {}
+
+  CatchEntryState(const CatchEntryState& state) { Copy(state); }
+
+  ~CatchEntryState() { Destroy(); }
+
+  CatchEntryState& operator=(const CatchEntryState& state) {
+    Destroy();
+    Copy(state);
+    return *this;
+  }
+
+  bool Empty() { return ref_count_ == NULL; }
+
+  intptr_t Pairs() { return data_[0]; }
+
+  intptr_t Src(intptr_t i) { return data_[1 + 2 * i]; }
+
+  intptr_t Dest(intptr_t i) {
+    return data_[2 + 2 * i] >> kCatchEntryStateDestShift;
+  }
+
+  bool isMove(intptr_t i) { return data_[2 + 2 * i] & kCatchEntryStateIsMove; }
+
+ private:
+  void Destroy() {
+    if (ref_count_ != NULL) {
+      (*ref_count_)--;
+      if (*ref_count_ == 0) {
+        delete ref_count_;
+        delete[] data_;
+      }
+    }
+  }
+
+  void Copy(const CatchEntryState& state) {
+    data_ = state.data_;
+    ref_count_ = state.ref_count_;
+    if (ref_count_ != NULL) {
+      (*ref_count_)++;
+    }
+  }
+
+  // data_ has the following format:
+  // 0 - number of pairs in this state
+  // 1-2 - 1st encoded src,dest pair
+  // 3-4 - 2nd pair
+  // ....
+  intptr_t* data_;
+  intptr_t* ref_count_;
+};
+
 }  // namespace dart
 
 #endif  // RUNTIME_VM_EXCEPTIONS_H_