What is the difference between Proguard and R8?

Question

The new version of Android Studio (3.4) just came out and brings with it default support for R8 instead of Proguard. Could someone explain the key differences between the two and any apparent benefits to using R8?

Answer 1

The history of Android build process kept changing and the developers are constantly trying to make it more efficient concerning build time and generated .dex file sizes. So, throughout the history there has been many variation of the process of generating .dex files from .java files.

Before R8 or D8, the Android build process involved these four steps;

SourceCode(.java) ---javac---> Java Bytecode(.class) ---Proguard---> Optimized Java bytecode(.class) ---Dex---> Dalvik Optimized Bytecode(.dex)

Then, the Android developers decided to merge all the steps in between to 1 step called Jack&Jill for optimization. However, this was introduced in 2015 and abandoned in 2017 due to not being flexible enough to work with all the growing development tools.

Then, D8 was introduced, which is a reverting back to original 4 step build process, with an optimized Dex transform. This implementation produced better quality bytecode than dx, with fewer instructions and better register allocation.

Now to R8, which has a similar goal with Jack&Jill as a starting point, merging two of these build steps into one. The Proguard and Dex step. So, instead of first Proguard processing the .class file returning again .class files and Dex/D8 processor taking in .class and returning .dex files, R8 merges these two steps, and takes in .class files, returning .dex files. This tool is still getting better, trying to optimize the build process even more. So, it is smart to migrate your project to R8 now, as it is a still growing tool which will be the default build tool soon. (As can be seen by enabled by default in the upgrade of Android Studio(3.4))

Also, the developers in Google issue tracker are very fast in returning to the issues reported about R8, as they are hungry for feedback and want to perfect this tool.

It has been reported that using R8 produces smaller .dex files, and does a more efficient minification of removing unused classes. This is a plus and a minus in some way. It is a plus obviously because smaller size is always better(in programming!),it is a minus because you have to intricately go through your code, and detect your entry points and reimplement the keep rules in your proguard file accordingly, as R8 introduces a more aggressive minification than Proguard.

For more information you can look into this article which includes very detailed explanation on R8 vs. Proguard: https://www.guardsquare.com/en/blog/proguard-and-r8

Also, this official speech from Google I/O 2018 : https://www.youtube.com/watch?v=x9T5EYE-QWQ&t=1194s

Hope this helps,