Kenneth Graunke <kenn...@whitecape.org> writes:
> With the previous optimization in place, some shaders wind up with
> multiple discard jumps in a row, or jumps directly to the next
> instruction. We can remove those.
>
> Without NIR on Haswell:
> total instructions in shared programs: 5777258 -> 5775872 (-0.02%)
> instructions in affected programs: 20312 -> 18926 (-6.82%)
> helped: 716
>
> With NIR on Haswell:
> total instructions in shared programs: 5773163 -> 5771785 (-0.02%)
> instructions in affected programs: 21040 -> 19662 (-6.55%)
> helped: 717
>
> v2: Use the CFG rather than the old instructions list. Presumably
> the placeholder halt will be in the last basic block.
>
> Signed-off-by: Kenneth Graunke <kenn...@whitecape.org>
> ---
> src/mesa/drivers/dri/i965/brw_fs.cpp | 42
> ++++++++++++++++++++++++++++++++++++
> src/mesa/drivers/dri/i965/brw_fs.h | 1 +
> 2 files changed, 43 insertions(+)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp
> b/src/mesa/drivers/dri/i965/brw_fs.cpp
> index 9df1650..21e1e82 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
> @@ -2558,6 +2558,47 @@ fs_visitor::opt_register_renaming()
> return progress;
> }
>
> +/**
> + * Remove redundant or useless discard jumps.
> + *
> + * For example, we can eliminate jumps in the following sequence:
> + *
> + * discard-jump (redundant with the next jump)
> + * discard-jump (useless; jumps to the next instruction)
> + * placeholder-halt
> + */
> +bool
> +fs_visitor::opt_redundant_discard_jumps()
> +{
> + bool progress = false;
> +
> + bblock_t *last_bblock = cfg->blocks[cfg->num_blocks - 1];
> +
> + fs_inst *placeholder_halt = NULL;
> + foreach_inst_in_block_reverse(fs_inst, inst, last_bblock) {
> + if (inst->opcode == FS_OPCODE_PLACEHOLDER_HALT) {
> + placeholder_halt = inst;
> + break;
> + }
> + }
> +
> + if (!placeholder_halt)
> + return false;
> +
> + /* Delete any HALTs immediately before the placeholder halt. */
> + for (fs_inst *prev = (fs_inst *) placeholder_halt->prev;
> + prev->opcode == FS_OPCODE_DISCARD_JUMP;
> + prev = (fs_inst *) placeholder_halt->prev) {
> + prev->remove(last_bblock);
> + progress = true;
> + }My only question in this series was "what if the placeholder halt is the first instruction in the block?" Shouldn't you be checking for a start sentinel? Other than that, this series is: Reviewed-by: Eric Anholt <e...@anholt.net> and I look forward to using the NIR intrinsic in my TGSI support.
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