[PATCH vkd3d] vkd3d-shader/hlsl: swizzle types of srcs can now be specified on sm4_instruction

[Zebediah Figura]

On 11/10/21 2:11 PM, Francisco Casas wrote:
> Some dxbc instructions require swizzle types that differ from what is
> usual for the register type.
> 
> e.g.
> gather4 requires a register with register type VKD3D_SM4_RT_SAMPLER but
> a swizzle type VKD3D_SM4_SWIZZLE_VEC4 instead of the usual
> VKD3D_SM4_SWIZZLE_NONE.

You could look at it that way, but I would rather say that "some 
register types do not use a consistent swizzle type." I.e. there's not 
really a "usual" case.

This is particularly true upon noticing that gather4 isn't the only 
"exception". For instance, I believe that single-element writemasks 
should in general result in SCALAR rather than VEC4 for normal temps.

Along those lines, I'd rather see sm4_swizzle_type() just go away, and 
the swizzle type explicitly specified everywhere. Introducing helpers 
like sm4_source_from_node() and sm4_source_from_deref() would make this 
easier.

As an aside, patch subjects should generally be phrased in the 
imperative. E.g. in this case I'd say something like "Allow using a 
custom swizzle type for sm4 source registers", or, if you end up 
following my suggestion, "Explicitly specify the swizzle type for sm4 
source registers".

> 
> The new fields of sm4_instruction can be used to handle these
> exceptions.
> 
> Also, they shouldn't change the current behaviour of the rest of
> the code since they are currently initalized with zeroes everywhere a
> sm4_instruction is initialized.

I think these paragraphs are obvious enough that they don't need to be 
in a patch description.