Win 10, GTX 880M, GTX 1080TI Founders Edition
Short description of error
Attached you'll finde a scene what has issues with GPU rendering. The scene is using the old shaders with a bevel shader (OSL).
The preview will not start or maybe it takes a very long time. Here nothing happened.
In GPU mode the preview starts as expected.
When I try to render with F12 in CPU mode it doesn't start or maybe it will start after a long time. Here nothing happened after 10 minutes.
When I render a small region with CPU it takes a long time till it starts to render.
When I start rendering in GPU mode it starts fast as expected ignoring OSL of course.
In the ZIP and attached you'll see a picture with a split screen. Left side is GPU. Right CPU. The results are different. Transparent parts with DOF will have extreme noise.
Exact steps for others to reproduce the error
Load the scene and press F12. Here CPU render will not start as expected.
Switch to GPU and press F12. Rendering will start.
Define a small region where the transparent parts are. Press F12. It will take really long but start. Result has noise at the transparent parts.
This might be a bug in the Cycles render engine or an issue with the shader tree.