[PATCH vkd3d 2/3] vkd3d-shader/hlsl: Take writemask into account when emitting a SM4 constant.

[Giovanni Mascellani]

Hi,

On 15/11/21 18:48, Zebediah Figura (she/her) wrote:
> This is probably quibbling, but how about this?
> 
> j = 0;
> for (i = 0; i < 4; ++i)
> {
>      if (instr.dsts[0].writemask & (1u << i))
>          instr.srcs[0].reg.immconst_uint[i] = constant->value[j++].u;
> }
> 
> Feels a bit simpler to me.

I agree it's simpler, but as written it's also wrong. :-)

The problem is that when dimx == 1, we set the register to have 
dimension VKD3D_SM4_DIMENSION_SCALAR, which means that the constant must 
be written in the first register, no matter the writemask.

I think that trying to accommodate for that thing lead me to uselessly 
convoluted code, because your proposal can be fixed to this:

j = 0;
for (i = 0; i < 4; ++i)
{
     if (dimx == 1 || instr.dsts[0].writemask & (1u << i))
         instr.srcs[0].reg.immconst_uint[i] = constant->value[j++].u;
}

This produces three useless writes for scalar registers, but hopefully 
that's not a big problem.

Thanks for the review, Giovanni.