Fix typeof optimization for undetectable

src/compiler/typer.cc

Index: src/compiler/typer.cc
diff --git a/src/compiler/typer.cc b/src/compiler/typer.cc
index 5fb20da9a5df17e8f6edf4cb87e1666dfa8aaa75..b670f52fbbec1003cbbd1db1cc51aaceb9b96f8e 100644
--- a/src/compiler/typer.cc
+++ b/src/compiler/typer.cc
@@ -291,6 +291,7 @@ class Typer::Visitor : public Reducer {
   static Type* ObjectIsSmi(Type*, Typer*);
   static Type* ObjectIsString(Type*, Typer*);
   static Type* ObjectIsUndetectable(Type*, Typer*);
+  static Type* TypeOfIsFunction(Type*, Typer*);
 
   static ComparisonOutcome JSCompareTyper(Type*, Type*, Typer*);
 
@@ -546,6 +547,11 @@ Type* Typer::Visitor::ObjectIsUndetectable(Type* type, Typer* t) {
   return Type::Boolean();
 }
 
+Type* Typer::Visitor::TypeOfIsFunction(Type* type, Typer* t) {
+  if (type->Is(Type::Function())) return t->singleton_true_;
+  if (!type->Maybe(Type::Function())) return t->singleton_false_;
+  return Type::Boolean();
+}
 
 // -----------------------------------------------------------------------------
 
@@ -1926,6 +1932,10 @@ Type* Typer::Visitor::TypeObjectIsUndetectable(Node* node) {
   return TypeUnaryOp(node, ObjectIsUndetectable);
 }
 
+Type* Typer::Visitor::TypeTypeOfIsFunction(Node* node) {
+  return TypeUnaryOp(node, TypeOfIsFunction);
+}
+
 Type* Typer::Visitor::TypeNewUnmappedArgumentsElements(Node* node) {
   return Type::OtherInternal();
 }