Re: [PATCH 0/1] MR179: vkd3d-shader/hlsl: Add support for ddx(), ddy() intrinsics.

[Nikolay Sivov (＠nsivov)]

I don't know if that's an optimization effect, but code in your example produces zero output unconditionally:

```
ps_4_0
dcl_output o0.xyzw
mov o0.xyzw, l(0,0,0,0)
ret 
```

I don't know how this works exactly, but maybe constant arguments produce 0 derivatives, and using expression that depends on certain semantics generates actual instructions.