EDIT: IMPORTANT: This thread is not for people to post wishlist for new features or design changes nor Brand discussions. Please post useful bug reports (with steps to reproduce, specs from your machine and files having the bug) and benchmark results (see further for details).
After seeing the RX 480 perfs I bought one and played a bit again with Cycles code to get some more performance.
The build is here https://ufile.io/90e0707. Depending on the scene, I got between 1.9x and 1.2x speedup on RX480.
It would be nice if you could report the rendering times of your card with those bench https://download.blender.org/demo/test/cycles_benchmark_20160228.zip with this build and with master to compare.
The BMW, Barcelona and fishy_cat are the most representative benchmark (product design, architecture and animation/cartoon).
With good datas from you, I may better improve the perfs, it’s a first draft.
For those with enough time, please post times with supported and experimental kernel.
Viewport render is also increased dramatically. Would be nice if you could post the times to render the BMW and Barcelona scene in the viewport. BMW has only one big viewport, render it until it has all samples. Same with Barcelona using the little 3D viewport in the bottom-right.
Have fun, it opens the door to really fast rendering to many artists
Edit: Patch is available here: https://developer.blender.org/D2254