Lets make it short.
When a Displacement-Node is attached to an Object the object is renderes completly Black.
This happens on Blender 2.80 and also on the dev Version 2.81
On CPU everything is fine.
Operating system: Linux-5.0.0-23-generic-x86_64-with-debian-buster-sid 64 Bits
Graphics card: Radeon RX Vega ATI Technologies Inc. 4.5.13564 Core Profile Context 22.214.171.124.7
Broken: version: 2.81 (sub 1), branch: master, commit date: 2019-08-08 20:54, hash: rB4c9fe657458f
Short description of error
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Exact steps for others to reproduce the error
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[Based on the default startup or an attached .blend file (as simple as possible)]