[PATCH vkd3d 1/3] vkd3d-shader/hlsl: Handle branches in copy propagation.

[Giovanni Mascellani]

Hi,

On 17/12/21 18:59, Zebediah Figura (she/her) wrote:
>> A new var_def is now initialized to the content of the same var_def
>> in earlier stack frames.
> 
> I'm not a big fan of this, because now it feels like it's half one thing 
> and half the other.

Neither I like it (my preferred solution is still my original proposal), 
but it was necessary to fix Matteo's changes, which hopefully you don't 
like either (since you found they are buggy). For the pars construens, 
which solution would you prefer now? Matteo, which alternative do you 
prefer?

> Something that just occurred to me: could we handle this by instead just 
> comparing the var_def structures from the parent and child state, and 
> invalidating where they don't match?
> 
> Alternatively, probably simpler: could we just recursively invalidate 
> parents in copy_propagation_record_store()?

I guess we could.

I don't like it because it makes it harder for me to convince myself 
that there is a proof of the correctness of the algorithm, and we have 
just seen that when it is harder to prove the correctness of an 
algorithm it is also easier that there are actual bugs; and on the other 
hand I see no points in favor in doing the changes (except perhaps for, 
in the case of the recursive var_def search, vague speculations about 
the fact that it might be a little faster.

Do you think that changing this would make it easier for you to check 
that the code is correct? Which other advantages do you see for the 
change your are proposing?

Thanks, Giovanni.