[Mesa-dev] [PATCH] register_allocate: don't consider trivially colorable registers for spilling.

[Eric Anholt]

Paul Berry <stereotype441 at gmail.com> writes:

> Previously, we considered all registers as candidates for spilling.
> This was counterproductive--for any registers that have already been
> removed from the interference graph, there is no benefit to spilling
> them, since they don't contribute to register pressure.
>
> This patch ensures that we will only try to spill registers that are
> still in the interference graph after register allocation has failed.
>
> This is consistent with the recommendations of the paper "Retargetable
> Graph-Coloring Register Allocation for Irregular Architectures", on
> which our register allocator is based.
> ---
>
> Note: I haven't found a shader whose performance is significantly
> improved by this patch (it seems that usually, our heuristics happen
> to select registers that are still in the interference graph), but it
> still seems justified on theoretical grounds.

Reviewed-by: Eric Anholt <eric at anholt.net>
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