[Mesa-dev] [PATCH 24/25] i965/fs: Skip gen4 pre/post-send dependency workaronds for the first/last block.

[Jason Ekstrand]

On Fri, May 27, 2016 at 7:06 PM, Francisco Jerez <currojerez at riseup.net>
wrote:

> We know that there cannot be any destination dependency race if we
> reach the beginning or end of the program without having found any
> other instruction the send could possibly race with.  This avoids
> emitting a pile of useless moves at the beginning or end of the
> program in the most common case in which the program has a single
> basic block only.
>
> On the original i965 I get the following shader-db results:
>
>  total instructions in shared programs: 3354165 -> 3215637 (-4.13%)
>  instructions in affected programs: 3183065 -> 3044537 (-4.35%)
>  helped: 13498
>  HURT: 0
>

Nice!


>
> ---
>  src/mesa/drivers/dri/i965/brw_fs.cpp | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp
> b/src/mesa/drivers/dri/i965/brw_fs.cpp
> index 660a8db..bfde69c 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
> @@ -3210,7 +3210,7 @@
> fs_visitor::insert_gen4_pre_send_dependency_workarounds(bblock_t *block,
>        /* If we hit control flow, assume that there *are* outstanding
>         * dependencies, and force their cleanup before our instruction.
>         */
> -      if (block->start() == scan_inst) {
> +      if (block->start() == scan_inst && block->num != 0) {
>

Yes, hitting the top of the program does *not* count as control flow.  Good
work us!

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>

--Jason


>           for (int i = 0; i < write_len; i++) {
>              if (needs_dep[i])
>                 DEP_RESOLVE_MOV(fs_builder(this, block, inst),
> @@ -3274,7 +3274,7 @@
> fs_visitor::insert_gen4_post_send_dependency_workarounds(bblock_t *block,
> fs_ins
>      */
>     foreach_inst_in_block_starting_from(fs_inst, scan_inst, inst) {
>        /* If we hit control flow, force resolve all remaining
> dependencies. */
> -      if (block->end() == scan_inst) {
> +      if (block->end() == scan_inst && block->num != cfg->num_blocks - 1)
> {
>           for (int i = 0; i < write_len; i++) {
>              if (needs_dep[i])
>                 DEP_RESOLVE_MOV(fs_builder(this, block, scan_inst),
> --
> 2.7.3
>
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