[Mesa-dev] [PATCH 01/14] i965: Don't copy propagate sat MOVs into LOAD_PAYLOAD

[Matt Turner]

On Tue, Oct 28, 2014 at 3:17 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:

I'm confused. This is the *constant* propagation function not copy
propagation, and if we're doing a mov.sat of an immediate, we can just
figure out what that is.

If you're seeing mov.sat with immediates, you should modify
opt_algebraic to remove them.