[Mesa-dev] [PATCH 00/10] i965: always mark used surfaces in the visitors

[Matt Turner]

On Fri, Oct 30, 2015 at 4:11 AM, Iago Toral Quiroga <itoral at igalia.com> wrote:
> Right now some opcodes that only use constant surface indexing mark them as
> used in the generator while others do it in the visitor. When the opcode can
> handle both direct and indirect surface indexing then some opcodes handle
> only the constant part in the generator and leave the indirect case to the
> caller. It is all very inconsistent and leads to confusion, since one has to
> go and look into the generator code in each case to check if it marks surfaces
> as used or not, and in which cases.
>
> when I was working on SSBOs I was tempted to try and fix this but then I
> forgot. Jordan bumped into this recently too when comparing visitor
> code paths for similar opcodes (ubos and ssbos) that need to handle this
> differently because they use different generator opcodes.
>
> Since the generator opcodes never handle marking of indirect surfaces, just
> leave surface marking to the caller completely, since callers always have
> all the information needed for this. It also makes things more consistent
> and clear for everyone: marking surfaces as used is always on the side
> of the visitor, never the generator.

What happens if we dead code eliminate the last texture() on a given
surface? Before in the constant indexed case, we wouldn't mark the
surface as used, but since this series moves that to the NIR ->
backend IR translation, presumably it'll still be marked used?

Is that important, and if so is there anything we can do to "unmark"
the unused surface?