Safe and efficient stack-limit based interrupt checking in C++.

runtime/vm/atomic.h

Index: runtime/vm/atomic.h
diff --git a/runtime/vm/atomic.h b/runtime/vm/atomic.h
index c256fe5e0a47dc660d474ffa740903ed8b99b165..6197f16ab7b7a2ad3669bd37d18a5e63d8122ba6 100644
--- a/runtime/vm/atomic.h
+++ b/runtime/vm/atomic.h
@@ -21,7 +21,11 @@ class AtomicOperations : public AllStatic {
   // that are accessed by generated code
   static uintptr_t FetchAndIncrement(uintptr_t* p);
 
+  static intptr_t FetchAndAdd(intptr_t* p, intptr_t delta);
+
   static uword CompareAndSwapWord(uword* ptr, uword old_value, uword new_value);
+
+  static uword LoadRelaxed(uword* ptr);
 };