Elide unnecessary context reload in generated stubs.

src/lithium.h

 // Copyright 2012 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 563 matching lines @@
       : env_(env),
         limit_(env != NULL ? env->values()->length() : 0),
         current_(0) {
     SkipUninteresting();
   }
 
   bool Done() { return current_ >= limit_; }
 
   LOperand* Current() {
     ASSERT(!Done());
+    ASSERT(env_->values()->at(current_) != NULL);
     return env_->values()->at(current_);
   }
 
   void Advance() {
     ASSERT(!Done());
     ++current_;
     SkipUninteresting();
   }
 
   LEnvironment* env() { return env_; }
@@ skipping 21 matching lines @@
  public:
   explicit DeepIterator(LEnvironment* env)
       : current_iterator_(env) {
     SkipUninteresting();
   }
 
   bool Done() { return current_iterator_.Done(); }
 
   LOperand* Current() {
     ASSERT(!current_iterator_.Done());
+    ASSERT(current_iterator_.Current() != NULL);
     return current_iterator_.Current();
   }
 
   void Advance() {
     current_iterator_.Advance();
     SkipUninteresting();
   }
 
  private:
   void SkipUninteresting() {
@@ skipping 68 matching lines @@
   ZoneList<Handle<JSFunction> > inlined_closures_;
 };
 
 
 int ElementsKindToShiftSize(ElementsKind elements_kind);
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_LITHIUM_H_