[Mesa-dev] [PATCH] st/mesa: keep track of saturated writes when eliminating dead code

[Ilia Mirkin]

On Wed, Sep 23, 2015 at 12:33 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> It doesn't matter whether a write is saturated or not, in another
> implementation it might even have been a separate opcode. This code was
> most likely copied from the copy-propagation pass (where one does have
> to distinguish saturation).
>
> Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
> ---
>
> Haven't run this through piglit yet, but happened upon it when I was
> debugging the other issue. (Which turned out to be an odd dependence
> on this pass by the regular emitter code.)

This doesn't seem to regress anything in piglit. Note that this change
isn't strictly required for correctness, but if we're going to do DCE,
might as well not mess it up arbitrarily. The effect was that
saturated ops (mov and maybe add) wouldn't get DCE'd.

>
>  src/mesa/state_tracker/st_glsl_to_tgsi.cpp | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> index 6762566..ee0acb5 100644
> --- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> +++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> @@ -4228,8 +4228,7 @@ glsl_to_tgsi_visitor::eliminate_dead_code(void)
>         */
>        for (unsigned i = 0; i < ARRAY_SIZE(inst->dst); i++) {
>           if (inst->dst[i].file == PROGRAM_TEMPORARY &&
> -             !inst->dst[i].reladdr &&
> -             !inst->saturate) {
> +             !inst->dst[i].reladdr) {
>              for (int c = 0; c < 4; c++) {
>                 if (inst->dst[i].writemask & (1 << c)) {
>                    if (writes[4 * inst->dst[i].index + c]) {
> --
> 2.4.9
>