[Heavy] Fix casting issues

Author: ricejasonf

heavy/lib/Context.cpp

@@ -1450,7 +1450,7 @@ heavy::Value ContextLocal::get(heavy::ContextLocalLookup const& C) const {
 heavy::Value ContextLocal::get_binding(
       heavy::ContextLocalLookup const& C) const {
   heavy::Value Value = C.LookupTable.lookup(key());
-  return dyn_cast<heavy::Binding>(Value);
+  return cast<heavy::Binding>(Value);
 }
 
 

heavy/lib/OpGen.cpp

@@ -689,7 +689,8 @@ mlir::Value OpGen::createSequence(SourceLocation Loc, Value Body) {
 //    in the lexical order that they were defined.
 bool OpGen::WalkDefineInits(Value Env,
                             llvm::SmallPtrSetImpl<String*>& LocalNames) {
-  Pair* P = cast<Pair>(Env);
+  Pair* P = dyn_cast<Pair>(Env);
+  if (!P) return false;
   if (isa<EnvFrame>(P->Car)) return false;
   if (WalkDefineInits(P->Cdr, LocalNames)) return true;