Osx 10.11.6 (MacBookPro11,5 Intel Core i7)
AMD Radeon R9-M370X
2.78-db8bc1d9829-OSX-10.6 (jul 21)
Short description of error
Denoising feature is not working on GPU rendering. It works on CPU rendering. Using Cycles.
Exact steps for others to reproduce the error
I just created a mokey with a diffuse shader and sun lamp. Denoising activated using default settings and rendered on CPU and GPU. Tested several times with similar corrupt image result on GPU.