Within the past few hours, Arceri has landed a number of the GLSL shader cache patches into mainline Mesa. This is work dating back years and originating with Intel Linux developers for allowing OpenGL GLSL shaders to be cached on-disk for speeding up load times and improving the performance for games that load shaders on the fly. This shader cache support has become much more pressing in the past year or two with more demanding games arriving for Linux, such as Shadow of Mordor being a good example.
While the core shader work has landed, as of writing this article, none of the driver-specific work has landed for actually enabling the shader cache functionality like in i965 or RadeonSI. But given this work now landing, the rest shouldn't be too far behind.