[turbofan] Test has been outsmarted by optimization.

test/mjsunit/fast-prototype.js

Index: test/mjsunit/fast-prototype.js
diff --git a/test/mjsunit/fast-prototype.js b/test/mjsunit/fast-prototype.js
index 2fb476ccb1645103a21e5dc2912c8aa3ef04ac9f..7432ecce9d7d6fee67f7a903208c15f381ab88db 100644
--- a/test/mjsunit/fast-prototype.js
+++ b/test/mjsunit/fast-prototype.js
@@ -50,8 +50,9 @@ function DoProtoMagic(proto, set__proto__) {
     (new Sub()).__proto__ = proto;
   } else {
     Sub.prototype = proto;
-    // Need to instantiate Sub to mark .prototype as prototype.
-    new Sub();
+    // Need to instantiate Sub to mark .prototype as prototype. Make sure the
+    // instantiated object is used so that the allocation is not optimized away.
+    %DebugPrint(new Sub());
   }
 }