[Mesa-dev] [PATCH v2 01/16] i965: Don't copy propagate sat MOVs into LOAD_PAYLOAD

[Matt Turner]

On Thu, Nov 13, 2014 at 4:28 PM, Kristian Høgsberg <krh at bitplanet.net> wrote:
> The LOAD_PAYLOAD opcode can't saturate its sources, so skip
> saturating MOVs.  The register coalescing after lower_load_payload()
> will clean up the extra MOVs.
>
> Signed-off-by: Kristian Høgsberg <krh at bitplanet.net>
> ---
>  src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> index e1989cb..87ea9c2 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> @@ -454,8 +454,12 @@ fs_visitor::try_constant_propagate(fs_inst *inst, acp_entry *entry)
>        val.effective_width = inst->src[i].effective_width;
>
>        switch (inst->opcode) {
> -      case BRW_OPCODE_MOV:
>        case SHADER_OPCODE_LOAD_PAYLOAD:
> +         /* LOAD_PAYLOAD can't sat its sources. */
> +         if (entry->saturate)
> +            break;
> +         /* Otherwise, fall through */
> +      case BRW_OPCODE_MOV:
>           inst->src[i] = val;
>           progress = true;
>           break;
> --
> 2.1.0

This looks like the same patch as 01/14 in the previous series. I
suggested a better approach there:

At the beginning of fs_visitor::try_constant_propagate, if
(entry->saturate) return false, or just saturate the argument and
proceed. We don't want to be propagating the result of a mov.sat 4.0
into anything without saturating the result first.