[Mesa-dev] [PATCH 28/57] i965/fs: Take into account copy register offset during compute-to-mrf.

[Iago Toral]

On Wed, 2016-09-07 at 18:48 -0700, Francisco Jerez wrote:
> This was dropping 'inst->dst.offset' on the floor.  Nothing in the
> code above seems to guarantee that it's zero and in that case the
> offset of the register being coalesced into wouldn't be taken into
> account while rewriting the generating instruction.
> ---
>  src/mesa/drivers/dri/i965/brw_fs.cpp | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp
> b/src/mesa/drivers/dri/i965/brw_fs.cpp
> index 98da06c..5b7ca98 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
> @@ -2821,7 +2821,7 @@ fs_visitor::compute_to_mrf()
>              }
>  
>              scan_inst->dst.file = MRF;
> -            scan_inst->dst.offset %= REG_SIZE;
> +            scan_inst->dst.offset = inst->dst.offset + scan_inst-
> >dst.offset % REG_SIZE;

So if we had something like this:

0: mov(4) r1.4:F r0.0:F
1: mov(4) m1:F r1.4:F

This pass is trying to get us:

mov(4) m1:F r0.0:F

In that case, the offset into the destination of the instruction we are propagating from should not affect the offset into the MRF we are writing to. Or maybe I am missing what is going on here :)

>              scan_inst->saturate |= inst->saturate;
>              if (!regs_left)
>                 break;