Noissue - Avoid try/catch triggering a deoptimization in message listener

messageResponder.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 22 matching lines @@
   var BlockingFilter = filterClasses.BlockingFilter;
   var RegExpFilter = filterClasses.RegExpFilter;
   var Synchronizer = require("synchronizer").Synchronizer;
 
   var info = require("info");
   var subscriptionClasses = require("subscriptionClasses");
   var Subscription = subscriptionClasses.Subscription;
   var DownloadableSubscription = subscriptionClasses.DownloadableSubscription;
   var SpecialSubscription = subscriptionClasses.SpecialSubscription;
 
+  // Some modules doesn't exist on Firefox. Moreover,
+  // require() throws an exception on Firefox in that case.
+  // However, try/catch causes the whole function to to be
+  // deoptimized on V8. So we wrap it into another function.
+  function tryRequire(module)
+  {
+    try
+    {
+      return require(module);
+    }
+    catch (e)
+    {
+      return null;
+    }
+  }
+
   function convertObject(keys, obj)
   {
     var result = {};
     for (var i = 0; i < keys.length; i++)
       result[keys[i]] = obj[keys[i]];
     return result;
   }
 
   var convertSubscription = convertObject.bind(null, ["disabled",
     "downloadStatus", "homepage", "lastDownload", "title", "url"]);
@@ skipping 78 matching lines @@
     return listenerFilters;
   }
 
   global.ext.onMessage.addListener(function(message, sender, callback)
   {
     switch (message.type)
     {
       case "app.get":
         if (message.what == "issues")
         {
-          var subscriptionInit;
-          try
-          {
-            subscriptionInit = require("subscriptionInit");
-          }
-          catch (e)
-          {
-            // Expected exception, this module doesn't exist on Firefox
-          }
-
+          var subscriptionInit = tryRequire("subscriptionInit");
           callback({
             filterlistsReinitialized: subscriptionInit ? subscriptionInit.reinitialized : false,
             legacySafariVersion: (info.platform == "safari" && (
                 Services.vc.compare(info.platformVersion, "6.0") < 0 ||   // beforeload breaks websites in Safari 5
                 Services.vc.compare(info.platformVersion, "6.1") == 0 ||  // extensions are broken in 6.1 and 7.0
                 Services.vc.compare(info.platformVersion, "7.0") == 0))
           });
         }
         else if (message.what == "doclink")
           callback(Utils.getDocLink(message.link));
@@ skipping 231 matching lines @@
           if (subscription instanceof DownloadableSubscription)
             Synchronizer.execute(subscription, true);
         }
         break;
       case "subscriptions.isDownloading":
         callback(Synchronizer.isExecuting(message.url));
         break;
     }
   });
 })(this);