[PATCH vkd3d 04/17] vkd3d-shader/hlsl: Propagate constant loads in copy propagation.

[Zebediah Figura (she/her)]

On 12/3/21 02:52, Giovanni Mascellani wrote:
> Hi,
> 
> On 02/12/21 17:17, Zebediah Figura wrote:
>> If this pass is going to be hard to write, I'm fine enough with using 
>> this patch as a temporary solution. It's not clear to me that the pass 
>> *is* hard to write, but it probably won't make it into 1.3 if that's 
>> going to be released soon. Of course, it's also not clear to me that 
>> we really *need* a temporary solution...
> 
> For sure we don't need it, but as much as we probably don't need most of 
> the other optimization passes we have, including copy propagation as a 
> whole (except for the bit about uniform objects). Whatever code we 
> compile to, it will eventually be re-compiled by a few other compilers, 
> at least one of which is probably better than ours and, more 
> importantly, knows about which hardware it is compiling for.
> 
> To me, optimization passes are currently mostly helpful to produce code 
> that can reasonably read by a human to verify that compilation is 
> correct. To this end, I think 4/17 is useful (as it will be a 
> vectorization pass, as soon as it will exist).

Well, we do sort of need copy-propagation so that we can deal with 
object variables (including e.g. object variables returned from a 
function, which I've seen in actual shaders). We can't translate those 
load/store instrs to actual DXBC, because there's no such thing as an 
object-typed temp.