[Mesa-dev] [PATCH 2/3] i965/fs: Make emit_uniformize a no-op for immediates

[Neil Roberts]

Just a thought, would it be better to move this check into the
eliminate_find_live_channel optimisation? That way it could catch
sources that become immediates through later optimisations. One problem
with this that I've seen before is that eliminating the
FIND_LIVE_CHANNEL doesn't cause the subsequent BROADCAST to be
eliminated because the copy propagation doesn't work. I made this patch
a while ago but I never posted it anywhere because it's a of a kludge
and it would probably be better to fix the copy propagation:

https://github.com/bpeel/mesa/commit/e4c3286075f891f466fb8558106d2aaa

Either way though I don't think it would do any harm to have Kristian's
patch as well even if we did improve elimintate_find_live_channel so it
is:

Reviewed-by: Neil Roberts <neil at linux.intel.com>

- Neil

Kristian Høgsberg Kristensen <krh at bitplanet.net> writes:

> An immdiate is already uniform so just return it up front. Without this,
> brw_fs_surface_builder ends up passing immediate surface indices through
> SHADER_OPCODE_BROADCAST. This writes to a stride 0 dst, which we can't
> constant propagate out of, and further, we don't constant propagate into
> the typed/untype read/write opcodes at all.  The end result is that all
> typed/untyped read/write/atomics end up as indirect sends.
>
> Code generation should always produce either an immediate or an actual
> indirect surface index, so we can fix this by just special casing
> immediates in emit_uniformize.
>
> Signed-off-by: Kristian Høgsberg Kristensen <krh at bitplanet.net>
> ---
>  src/mesa/drivers/dri/i965/brw_fs_builder.h | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_fs_builder.h b/src/mesa/drivers/dri/i965/brw_fs_builder.h
> index df10a9d..98ce71e 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_builder.h
> +++ b/src/mesa/drivers/dri/i965/brw_fs_builder.h
> @@ -394,6 +394,9 @@ namespace brw {
>           const dst_reg chan_index = component(vgrf(BRW_REGISTER_TYPE_UD), 0);
>           const dst_reg dst = component(vgrf(src.type), 0);
>  
> +         if (src.file == IMM)
> +            return src;
> +
>           ubld.emit(SHADER_OPCODE_FIND_LIVE_CHANNEL, chan_index);
>           ubld.emit(SHADER_OPCODE_BROADCAST, dst, src, chan_index);
>  
> -- 
> 2.6.2
>
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