Unify the handling of comparinsons against null and undefined.

src/ast.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 270 matching lines @@
   // (faster) prefix increments.
   virtual void MarkAsStatement() { /* do nothing */ }
 
   // True iff the result can be safely overwritten (to avoid allocation).
   // False for operations that can return one of their operands.
   virtual bool ResultOverwriteAllowed() { return false; }
 
   // True iff the expression is a literal represented as a smi.
   virtual bool IsSmiLiteral() { return false; }
 
+  // True iff the expression is a string literal.
+  virtual bool IsStringLiteral() { return false; }
+
+  // True iff the expression is the null literal.
+  virtual bool IsNullLiteral() { return false; }
+
   // Type feedback information for assignments and properties.
   virtual bool IsMonomorphic() {
     UNREACHABLE();
     return false;
   }
   virtual bool IsArrayLength() {
     UNREACHABLE();
     return false;
   }
   virtual SmallMapList* GetReceiverTypes() {
@@ skipping 582 matching lines @@
 
 class Literal: public Expression {
  public:
   Literal(Isolate* isolate, Handle<Object> handle)
       : Expression(isolate), handle_(handle) { }
 
   DECLARE_NODE_TYPE(Literal)
 
   virtual bool IsTrivial() { return true; }
   virtual bool IsSmiLiteral() { return handle_->IsSmi(); }
+  virtual bool IsStringLiteral() { return handle_->IsString(); }
+  virtual bool IsNullLiteral() { return handle_->IsNull(); }
 
   // Check if this literal is identical to the other literal.
   bool IsIdenticalTo(const Literal* other) const {
     return handle_.is_identical_to(other->handle_);
   }
 
   virtual bool IsPropertyName() {
     if (handle_->IsSymbol()) {
       uint32_t ignored;
       return !String::cast(*handle_)->AsArrayIndex(&ignored);
@@ skipping 1218 matching lines @@
 
  private:
   Isolate* isolate_;
   bool stack_overflow_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_AST_H_