[Mesa-dev] [PATCH] i965: Make exec_size 16 word/byte registers use exec_size halving again.

Kenneth Graunke kenneth at whitecape.org
Fri May 13 17:59:39 UTC 2016

On Friday, May 13, 2016 3:39:29 AM PDT Connor Abbott wrote:
> My understanding is that compression isn't necessary here, at least on
> newer gens (I don't know much about gen4/5). Could you explain why a
> <16,16,1>:w region is illegal? It would be nice to get a PRM citation
> in the comment below.

Matt mentioned it was illegal in a bugzilla comment, but it certainly
seems legal to me, at least with W types.  However,  we /are/ using
compression...and using both together seems wrong...

fs_generator::generate_code() contains:

   if (dispatch_width == 16)
      brw_set_default_compression_control(p, BRW_COMPRESSION_COMPRESSED);

It looks like we also have code a little ways down to set compression
control based on the register region, so maybe we don't the above code.
But I'm kind of hesitant to delete it - we might need it for some
instructions like IF which don't have sources/destinations.

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