Use R8 To Shrink, Optimize, and Speed Up Apps
Article Summary
Ben Weiss from Google reveals the single most impactful, low-effort change you can make to Android app performance. Reddit saw 40% faster cold startup and Disney+ cut ANRs by 25% with one configuration tweak.
Google's Android Performance Spotlight Week kicks off with a deep dive into R8, the optimizer that does far more than shrink app size. While most developers know R8 for removing unused code, its real power lies in whole-program optimizations that fundamentally rewrite code for efficiency.
Key Takeaways
- Reddit achieved 40% faster startup and 30% fewer ANRs after enabling R8 full mode
- Disney+ saw 30% faster startup by replacing one default configuration file
- R8 performs method inlining, class merging, and tree shaking for runtime gains
- Many apps still use proguard-android.txt which contains the -dontoptimize flag
- AGP 9.0 adds automatic stack trace de-obfuscation in Android Studio logcat
Enabling R8's full mode delivers measurable performance wins (25-40% improvements) with minimal code changes, yet many apps still have optimization accidentally disabled.
About This Article
Developers struggle to configure R8 properly. Keep Rules are especially hard to understand and use correctly when dealing with code that's accessed through reflection or JNI.
Google improved its documentation for R8. The new guides cover Keep Rules in detail, include real-world examples, and add sections on testing, troubleshooting, and advanced setups for library authors.
Developers can now adopt R8 step by step without worrying as much about accidentally removing code they need. They also get access to whole-program optimization benefits.