[Mesa-dev] [PATCH 11/20] i965/fs: Allow emit_uniformize() to broadcast a specific channel

[Francisco Jerez]

Matt Turner <mattst88 at gmail.com> writes:

> This function will be used to implement read_invocation (by specifying a
> specific channel) and read_first_invocation (by not specifying a
> channel).
> ---
>  src/intel/compiler/brw_fs_builder.h | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/src/intel/compiler/brw_fs_builder.h b/src/intel/compiler/brw_fs_builder.h
> index 87394bc17b..144ee54916 100644
> --- a/src/intel/compiler/brw_fs_builder.h
> +++ b/src/intel/compiler/brw_fs_builder.h
> @@ -393,7 +393,7 @@ namespace brw {
>         * Copy any live channel from \p src to the first channel of the result.
>         */
>        src_reg
> -      emit_uniformize(const src_reg &src) const
> +      emit_uniformize(const src_reg &src, dst_reg chan_index = dst_reg()) const
>        {
>           /* FIXME: We use a vector chan_index and dst to allow constant and
>            * copy propagration to move result all the way into the consuming
> @@ -403,10 +403,13 @@ namespace brw {
>            * should go back to scalar destinations here.
>            */
>           const fs_builder ubld = exec_all();
> -         const dst_reg chan_index = vgrf(BRW_REGISTER_TYPE_UD);
>           const dst_reg dst = vgrf(src.type);
>  
> -         ubld.emit(SHADER_OPCODE_FIND_LIVE_CHANNEL, chan_index);
> +         if (chan_index.file == BAD_FILE) {
> +            chan_index = vgrf(BRW_REGISTER_TYPE_UD);
> +            ubld.emit(SHADER_OPCODE_FIND_LIVE_CHANNEL, chan_index);
> +         }
> +

I don't like re-using emit_uniformize() (which is supposed to give you
the value of a channel of the input it can prove live as the doxygen
comment explains), as a "fetch me the i-th channel of the source"
helper.  I think what you want is just BROADCAST -- Why don't you just
emit the one BROADCAST instruction yourself?

>           ubld.emit(SHADER_OPCODE_BROADCAST, dst, src, component(chan_index, 0));
>  
>           return src_reg(component(dst, 0));
> -- 
> 2.13.0
>
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