Google has now come up with a new compiler for Android, the D8. This one is basically improved and efficient compared to the DX compiler.
Google had shipped the D8 compiler along with Android Studio 3.0 with a opt-in feature.
In the initial phase the default compiler would be DX, then Google will deprecate it in later phase.
If you want to use D8 in you builds, then modify your gradle.properties with this
android.enableD8 = false