Dead code elimination for web systems written in PHP: Lessons learned from an industry case

Web systems undergo constant evolution. This makes them prone to accumulating dead code. In turn, dead code is commonly understood to inhibit software evolution. The only way out of this vicious circle is the careful analysis of the web system, identifying unused features, and eliminating them. However, modern web systems are often built with server side scripting languages such as PHP. Their inherent dynamic features render traditional static dead code identification approaches useless. We describe the technical issues involved in detecting dead PHP code, and propose an identification and removal approach based on dynamic analysis. Further, we describe the examination of our approach in an industry-scale web system, and discuss our lessons learned.