We fallback to Sharp closures for Glossy, Glass and Refraction nodes now, in case the Roughness input is disconnected and 0 (< 1e-4f to be exact).
This way we gain a few percentages of performance, in case the user did not manually set the closure type to "Sharp" in the UI.
Sharp will probably be removed from the UI as a followup, not needed anymore with this internal optimization.
Original idea by Lukas Stockner(Differential Revision: https://developer.blender.org/D1439), code implementation by myself.
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