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nir/peephole_select: allow ballot

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We can allow collapsing control flow around ballot if we update the ballot
condition like we do for discards.

ballot_relaxed needs no condition update, as the result bits are undefined
for inactive invocations.

Foz-DB Navi21:
Totals from 27 (0.03% of 97591) affected shaders:
Instrs: 2554506 -> 2554469 (-0.00%); split: -0.00%, +0.00%
CodeSize: 13765636 -> 13765684 (+0.00%); split: -0.00%, +0.00%
Latency: 14186667 -> 14186861 (+0.00%); split: -0.00%, +0.00%
InvThroughput: 3542516 -> 3542595 (+0.00%); split: -0.00%, +0.00%
SClause: 52038 -> 52030 (-0.02%)
Copies: 209410 -> 208763 (-0.31%)
Branches: 83716 -> 83399 (-0.38%)
PreSGPRs: 2372 -> 2386 (+0.59%); split: -0.17%, +0.76%
VALU: 1701458 -> 1701482 (+0.00%)
SALU: 369884 -> 370107 (+0.06%); split: -0.00%, +0.07%
SMEM: 67643 -> 67634 (-0.01%)

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38828>
This commit is contained in:
Georg Lehmann 2025-12-05 12:01:49 +01:00 • committed by Marge Bot
parent 077b654cc7
commit 005cc4110c
1 changed files with 21 additions and 10 deletions
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31
src/compiler/nir/nir_opt_peephole_select.c
View file

@ -200,6 +200,8 @@ block_check_for_allowed_instrs(nir_block *block, unsigned *count,
case nir_intrinsic_ddy_fine:
case nir_intrinsic_ddy_coarse:
case nir_intrinsic_load_const_ir3:
case nir_intrinsic_ballot:
case nir_intrinsic_ballot_relaxed:
if (!alu_ok)
return false;
break;
@ -316,9 +318,11 @@ get_options_for_if(nir_if *if_stmt,
return if_options;
}
/* If we're moving discards out of the if we need to add the if's condition to it */
/* If we're moving discards or other conditional intrinsics
* out of the if we need to add the if's condition to it
*/
static void
rewrite_discard_conds(nir_instr *instr, nir_def *if_cond, bool is_else)
rewrite_intrinsic_conds(nir_instr *instr, nir_def *if_cond, bool is_else)
{
if (instr->type != nir_instr_type_intrinsic)
return;
@ -327,18 +331,25 @@ rewrite_discard_conds(nir_instr *instr, nir_def *if_cond, bool is_else)
if (intr->intrinsic != nir_intrinsic_terminate_if &&
intr->intrinsic != nir_intrinsic_terminate &&
intr->intrinsic != nir_intrinsic_demote_if &&
intr->intrinsic != nir_intrinsic_demote)
intr->intrinsic != nir_intrinsic_demote &&
intr->intrinsic != nir_intrinsic_ballot)
return;
nir_builder b = nir_builder_at(nir_before_instr(instr));
if (is_else)
if_cond = nir_inot(&b, if_cond);
if (intr->intrinsic == nir_intrinsic_terminate_if ||
intr->intrinsic == nir_intrinsic_demote_if) {
intr->intrinsic == nir_intrinsic_demote_if ||
intr->intrinsic == nir_intrinsic_ballot) {
if_cond = nir_b2bN(&b, if_cond, intr->src[0].ssa->bit_size);
if (is_else)
if_cond = nir_inot(&b, if_cond);
nir_src_rewrite(&intr->src[0], nir_iand(&b, intr->src[0].ssa, if_cond));
} else {
if (is_else)
if_cond = nir_inot(&b, if_cond);
if (intr->intrinsic == nir_intrinsic_terminate)
nir_terminate_if(&b, if_cond);
else
@ -447,7 +458,7 @@ nir_opt_collapse_if(nir_if *if_stmt, nir_shader *shader,
/* combine condition with potential demote/terminate */
nir_foreach_instr_safe(instr, first)
rewrite_discard_conds(instr, parent_if->condition.ssa, false);
rewrite_intrinsic_conds(instr, parent_if->condition.ssa, false);
/* combine the if conditions */
struct nir_builder b = nir_builder_at(nir_before_cf_node(&if_stmt->cf_node));
@ -526,14 +537,14 @@ nir_opt_peephole_select_block(nir_block *block, nir_shader *shader,
exec_node_remove(&instr->node);
instr->block = prev_block;
exec_list_push_tail(&prev_block->instr_list, &instr->node);
rewrite_discard_conds(instr, if_stmt->condition.ssa, false);
rewrite_intrinsic_conds(instr, if_stmt->condition.ssa, false);
}
nir_foreach_instr_safe(instr, else_block) {
exec_node_remove(&instr->node);
instr->block = prev_block;
exec_list_push_tail(&prev_block->instr_list, &instr->node);
rewrite_discard_conds(instr, if_stmt->condition.ssa, true);
rewrite_intrinsic_conds(instr, if_stmt->condition.ssa, true);
}
nir_foreach_phi_safe(phi, block) {