Re: [PATCH 0/2] MR784: tests: Check that derivatives are still computed after discarding.

[Henri Verbeet (＠hverbeet)]

> I can see that the generates shaders have `OpKill` or `OpDemoteToHelperInvocationEXT` depending on whether they're on the Vulkan or D3D12 runner, but in practice the effect seems to be the same on all the drivers I tested. It doesn't look like that the SPIR-V specs tells a lot about what is ought to happen when derivatives are computer after `OpKill`, so I assume it's unspecified and drivers treat that as `OpDemoteToHelperInvocationEXT` anyway.

I suppose, which is perhaps unfortunate. We should probably enable the extension in any case for the Vulkan runner to get defined behaviour though.