I'm not quite sure about VKD3D_SHADER_ERROR_IR_REGISTER_ORDER_TOO_HIGH. On the one hand, it makes sense that we'd have our own errors on the IR level. On the other hand, this feels like something the TPF frontend should have caught and emitted an error for while parsing. Perhaps others have opinions?
That does sound like something the DXBC frontend should validate rather than the normalizer.