What does R8 Full Mode really do? (aggressive optimizations)

What does R8 Full Mode really do? (aggressive optimizations)

R8 is a powerful code shrinking, obfuscation, and optimization tool that is part of the Android Gradle Plugin. It’s designed to improve the performance and size of your Android applications. One of the most talked-about features of R8 is its **Full Mode**, which offers a set of aggressive optimizations that can significantly impact your app’s size and performance. But what exactly does Full Mode do?

R8 Full Mode Explained

R8’s Full Mode is a **highly-optimized code processing mode**. It’s not just a simple code shrinker, but a complex tool that utilizes various advanced optimizations to improve your app. Here’s a breakdown of what R8 Full Mode does:

1. Code Shrinking (Removal of unused code)

R8 analyzes your code and identifies unused classes, methods, and fields. It then removes this unused code from your APK. This significantly reduces the size of your app.

2. Code Obfuscation

R8 can rename classes, methods, and fields to shorter, less meaningful names. This makes it harder for attackers to reverse engineer your code. Obfuscation can further shrink your APK.

3. Code Optimization

R8 applies several optimizations, such as:

• **Method Inlining:** Replaces method calls with the actual method body, reducing method overhead and improving performance.
• **Constant Folding:** Pre-calculates constant expressions at compile time, avoiding runtime calculation.
• **Dead Code Elimination:** Removes code that has no effect on the application’s execution.
• **Class Merging:** Merges classes with similar functionality, reducing the number of classes in your APK.

4. Tree Shaking

R8 eliminates unused code that’s brought in through dependencies. It can even remove entire libraries if they are not utilized in your app.

5. Dex Optimizations

R8 optimizes the structure of the DEX files, which contain your compiled code, making them smaller and faster to load.

Comparing Full Mode with Other Optimization Modes

Full Mode offers the **most extensive set of optimizations** compared to other modes. While Proguard provides basic code shrinking, obfuscation, and optimization, Full Mode goes further with tree shaking, Dex optimizations, and more advanced code optimization techniques.

Enabling R8 Full Mode

Enabling R8 Full Mode is straightforward. Simply add the following lines to your module-level build.gradle file:

android {
    buildTypes {
        release {
            minifyEnabled true
            shrinkResources true
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

These settings enable code shrinking, resource shrinking, and specify the Proguard rules to be applied. It’s important to note that these settings are typically already configured in your project when you select the “Release” build variant.

Considerations for using R8 Full Mode

While Full Mode offers significant benefits, it’s important to consider the following:

• **Potential Build Time Increase:** Full Mode can significantly increase build time, especially for large projects. You might need to adjust your build configuration or utilize build caching to mitigate this.
• **Testing is Crucial:** Always test your application thoroughly after enabling Full Mode to ensure it’s working as expected. The aggressive optimizations could potentially introduce unexpected behavior.
• **Proguard Rules:** Carefully craft Proguard rules to ensure your app’s essential functionalities are preserved. It’s a good practice to add Proguard rules to your project early on and maintain them as your project grows.

Conclusion

R8 Full Mode is a powerful tool for improving the performance and size of your Android applications. It applies aggressive code shrinking, obfuscation, and optimization techniques that go beyond traditional tools. However, it’s important to understand the potential impact of these optimizations, test your application thoroughly, and carefully manage your Proguard rules to avoid unintended consequences. When used effectively, Full Mode can significantly enhance the quality and efficiency of your Android app.