Infer whether a variable is assigned

src/variables.h

Index: src/variables.h
diff --git a/src/variables.h b/src/variables.h
index de209d871d56da5b77588b2eaeeec1ae5b484be5..3d67ff80a421cd332ff8a6a242fede882fc19ff9 100644
--- a/src/variables.h
+++ b/src/variables.h
@@ -80,7 +80,9 @@ class Variable: public ZoneObject {
     force_context_allocation_ = true;
   }
   bool is_used() { return is_used_; }
-  void set_is_used(bool flag) { is_used_ = flag; }
+  void set_is_used() { is_used_ = true; }
+  bool maybe_assigned() { return maybe_assigned_; }
+  void set_maybe_assigned() { maybe_assigned_ = true; }
 
   int initializer_position() { return initializer_position_; }
   void set_initializer_position(int pos) { initializer_position_ = pos; }
@@ -155,6 +157,7 @@ class Variable: public ZoneObject {
   // Usage info.
   bool force_context_allocation_;  // set by variable resolver
   bool is_used_;
+  bool maybe_assigned_;
   InitializationFlag initialization_flag_;
 
   // Module type info.