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nir/opt_if: See through inot

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Consider

    if (!x) {
       if (x) {
          ...
       }
    }

The inner use of `x` must be false, but so far only instances of `!x`
would have been replaced with a constant. See through the `inot` to
replace instances of `x` as well.

shader-db:

Lunar Lake
total instructions in shared programs: 17205147 -> 17204908 (<.01%)
instructions in affected programs: 56037 -> 55798 (-0.43%)
helped: 79 / HURT: 79

total cycles in shared programs: 879847886 -> 879992944 (0.02%)
cycles in affected programs: 5244138 -> 5389196 (2.77%)
helped: 141 / HURT: 125

Meteor Lake, DG2, and Tiger Lake had similar results. (Meteor Lake shown)
total instructions in shared programs: 19968312 -> 19968069 (<.01%)
instructions in affected programs: 65698 -> 65455 (-0.37%)
helped: 88 / HURT: 104

total cycles in shared programs: 884331007 -> 884469865 (0.02%)
cycles in affected programs: 4839695 -> 4978553 (2.87%)
helped: 172 / HURT: 136

LOST:   3
GAINED: 0

Ice Lake, Skylake, and Broadwell had similar results. (Ice Lake shown)
total instructions in shared programs: 20809765 -> 20809473 (<.01%)
instructions in affected programs: 65976 -> 65684 (-0.44%)
helped: 89 / HURT: 102

total cycles in shared programs: 872466849 -> 872433762 (<.01%)
cycles in affected programs: 5452888 -> 5419801 (-0.61%)
helped: 157 / HURT: 133

total spills in shared programs: 4014 -> 4010 (-0.10%)
spills in affected programs: 30 -> 26 (-13.33%)
helped: 1 / HURT: 0

total fills in shared programs: 3769 -> 3765 (-0.11%)
fills in affected programs: 50 -> 46 (-8.00%)
helped: 1 / HURT: 0

LOST:   3
GAINED: 1

fossil-db:

All Intel platforms had similar results. (Lunar Lake shown)
Totals:
Instrs: 910122459 -> 910097570 (-0.00%); split: -0.00%, +0.00%
Subgroup size: 40045664 -> 40046176 (+0.00%)
Send messages: 40724361 -> 40724036 (-0.00%)
Loop count: 970500 -> 970054 (-0.05%)
Cycle count: 105785543442 -> 105794147978 (+0.01%); split: -0.02%, +0.02%
Spill count: 3426093 -> 3426032 (-0.00%); split: -0.00%, +0.00%
Fill count: 6525296 -> 6525210 (-0.00%); split: -0.00%, +0.00%
Max live registers: 188561553 -> 188519064 (-0.02%); split: -0.02%, +0.00%
Max dispatch width: 47958304 -> 47958496 (+0.00%); split: +0.00%, -0.00%
Non SSA regs after NIR: 227303232 -> 227296055 (-0.00%); split: -0.00%, +0.00%

Totals from 15417 (0.78% of 1977988) affected shaders:
Instrs: 16984488 -> 16959599 (-0.15%); split: -0.20%, +0.05%
Subgroup size: 512 -> 1024 (+100.00%)
Send messages: 900193 -> 899868 (-0.04%)
Loop count: 23059 -> 22613 (-1.93%)
Cycle count: 1200149390 -> 1208753926 (+0.72%); split: -1.48%, +2.20%
Spill count: 25838 -> 25777 (-0.24%); split: -0.29%, +0.06%
Fill count: 43627 -> 43541 (-0.20%); split: -0.28%, +0.08%
Max live registers: 2550741 -> 2508252 (-1.67%); split: -1.75%, +0.08%
Max dispatch width: 296736 -> 296928 (+0.06%); split: +0.08%, -0.02%
Non SSA regs after NIR: 3264670 -> 3257493 (-0.22%); split: -0.25%, +0.03%

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38196>
This commit is contained in:
Ian Romanick 2025-10-22 13:45:20 -07:00 • committed by Marge Bot
parent 27d9e4ec2a
commit 67a6fc0160
1 changed files with 34 additions and 10 deletions
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44
src/compiler/nir/nir_opt_if.c
View file

@ -835,14 +835,14 @@ opt_if_phi_is_condition(nir_builder *b, nir_if *nif)
}
static bool
evaluate_if_condition(nir_if *nif, nir_cursor cursor, bool *value)
evaluate_if_condition(nir_if *nif, nir_cursor cursor, bool *value, bool invert)
{
nir_block *use_block = nir_cursor_current_block(cursor);
if (nir_block_dominates(nir_if_first_then_block(nif), use_block)) {
*value = true;
*value = !invert;
return true;
} else if (nir_block_dominates(nir_if_first_else_block(nif), use_block)) {
*value = false;
*value = invert;
return true;
} else {
return false;
@ -922,11 +922,11 @@ clone_alu_and_replace_src_defs(nir_builder *b, const nir_alu_instr *alu,
*/
static bool
propagate_condition_eval(nir_builder *b, nir_if *nif, nir_src *use_src,
nir_src *alu_use, nir_alu_instr *alu)
nir_src *alu_use, nir_alu_instr *alu, bool invert)
{
bool bool_value;
b->cursor = nir_before_src(alu_use);
if (!evaluate_if_condition(nif, b->cursor, &bool_value))
if (!evaluate_if_condition(nif, b->cursor, &bool_value, invert))
return false;
nir_def *def[NIR_MAX_VEC_COMPONENTS] = { 0 };
@ -965,14 +965,15 @@ can_propagate_through_alu(nir_src *src)
}
static bool
evaluate_condition_use(nir_builder *b, nir_if *nif, nir_src *use_src)
evaluate_condition_use(nir_builder *b, nir_if *nif, nir_src *use_src,
bool invert)
{
bool progress = false;
b->cursor = nir_before_src(use_src);
bool bool_value;
if (evaluate_if_condition(nif, b->cursor, &bool_value)) {
if (evaluate_if_condition(nif, b->cursor, &bool_value, invert)) {
/* Rewrite use to use const */
nir_src_rewrite(use_src, nir_imm_bool(b, bool_value));
progress = true;
@ -981,8 +982,10 @@ evaluate_condition_use(nir_builder *b, nir_if *nif, nir_src *use_src)
if (!nir_src_is_if(use_src) && can_propagate_through_alu(use_src)) {
nir_alu_instr *alu = nir_instr_as_alu(nir_src_parent_instr(use_src));
nir_foreach_use_including_if_safe(alu_use, &alu->def)
progress |= propagate_condition_eval(b, nif, use_src, alu_use, alu);
nir_foreach_use_including_if_safe(alu_use, &alu->def) {
progress |= propagate_condition_eval(b, nif, use_src, alu_use, alu,
invert);
}
}
return progress;
@ -996,7 +999,28 @@ opt_if_evaluate_condition_use(nir_builder *b, nir_if *nif)
/* Evaluate any uses of the if condition inside the if branches */
nir_foreach_use_including_if_safe(use_src, nif->condition.ssa) {
if (!(nir_src_is_if(use_src) && nir_src_parent_if(use_src) == nif))
progress |= evaluate_condition_use(b, nif, use_src);
progress |= evaluate_condition_use(b, nif, use_src, false);
}
nir_alu_instr *alu = nir_src_as_alu_instr(nif->condition);
if (alu != NULL && alu->op == nir_op_inot &&
nir_src_num_components(alu->src[0].src) == 1) {
/* Consider
*
* if (!x) {
* if (x) {
* ...
* }
* }
*
* The inner use of x must be false, but so far only instances of !x
* would have been replaced with a constant. See through the inot to
* replace instances of x as well.
*/
nir_foreach_use_including_if_safe(use_src, alu->src[0].src.ssa) {
if (nir_src_is_if(use_src) || nir_src_parent_instr(use_src) != &alu->instr)
progress |= evaluate_condition_use(b, nif, use_src, true);
}
}
return progress;