Since we know what side of the branch we ended up on we can just
replace the use with a constant.
All the spill changes in shader-db are from Dolphin uber shaders,
despite some small regressions the change is clearly positive.
V2: insert new constant after any phis in the
use->parent_instr->type == nir_instr_type_phi path.
v3:
- use nir_after_block_before_jump() for inserting const
- check dominance of phi uses correctly
shader-db results IVB:
total instructions in shared programs: 9999201 -> 9993483 (-0.06%)
instructions in affected programs: 163235 -> 157517 (-3.50%)
helped: 132
HURT: 2
total cycles in shared programs: 231670754 -> 219476091 (-5.26%)
cycles in affected programs: 143424120 -> 131229457 (-8.50%)
helped: 115
HURT: 24
total spills in shared programs: 4383 -> 4370 (-0.30%)
spills in affected programs: 1656 -> 1643 (-0.79%)
helped: 9
HURT: 18
total fills in shared programs: 4610 -> 4581 (-0.63%)
fills in affected programs: 374 -> 345 (-7.75%)
helped: 6
HURT: 0
---
src/compiler/nir/nir_opt_if.c | 135 ++++++++++++++++++++++++++++++++++
1 file changed, 135 insertions(+)
diff --git a/src/compiler/nir/nir_opt_if.c b/src/compiler/nir/nir_opt_if.c
index dacf2d6c667..8c886041708 100644
--- a/src/compiler/nir/nir_opt_if.c
+++ b/src/compiler/nir/nir_opt_if.c
@@ -369,6 +369,98 @@ opt_if_loop_terminator(nir_if *nif)
return true;
}
+static void
+replace_if_condition_use_with_const(nir_src *use, unsigned nir_boolean,
+ void *mem_ctx, bool if_condition)
+{
+ /* Create const */
+ nir_load_const_instr *load = nir_load_const_instr_create(mem_ctx, 1, 32);
+ load->value.u32[0] = nir_boolean;
+
+ if (if_condition) {
+ nir_instr_insert_before_cf(&use->parent_if->cf_node, &load->instr);
+ } else if (use->parent_instr->type == nir_instr_type_phi) {
+ nir_phi_instr *cond_phi = nir_instr_as_phi(use->parent_instr);
+
+ bool UNUSED found = false;
+ nir_foreach_phi_src(phi_src, cond_phi) {
+ if (phi_src->src.ssa == use->ssa) {
+ nir_instr_insert(nir_after_block_before_jump(phi_src->pred),
+ &load->instr);
+ found = true;
+ break;
+ }
+ }
+ assert(found);
+ } else {
+ nir_instr_insert_before(use->parent_instr, &load->instr);
+ }
+
+ /* Rewrite use to use const */
+ nir_src new_src = nir_src_for_ssa(&load->def);
+
+ if (if_condition)
+ nir_if_rewrite_condition(use->parent_if, new_src);
+ else
+ nir_instr_rewrite_src(use->parent_instr, use, new_src);
+}
+
+static bool
+evaluate_condition_use(nir_if *nif, nir_src *use_src, void *mem_ctx,
+ bool if_condition)
+{
+ bool progress = false;
+
+ nir_block *use_block = NULL;
+ if (if_condition) {
+ use_block =
+ nir_cf_node_as_block(nir_cf_node_prev(&use_src->parent_if->cf_node));
+ } else if (use_src->parent_instr->type == nir_instr_type_phi) {
+ nir_phi_instr *cond_phi = nir_instr_as_phi(use_src->parent_instr);
+
+ nir_foreach_phi_src(phi_src, cond_phi) {
+ if (phi_src->src.ssa == use_src->ssa) {
+ use_block = phi_src->pred;
+ break;
+ }
+ }
+ assert(use_block);
+ } else {
+ use_block = use_src->parent_instr->block;
+ }
+
+ if (nir_block_dominates(nir_if_first_then_block(nif), use_block)) {
+ replace_if_condition_use_with_const(use_src, NIR_TRUE, mem_ctx,
+ if_condition);
+ progress = true;
+ } else if (nir_block_dominates(nir_if_first_else_block(nif), use_block)) {
+ replace_if_condition_use_with_const(use_src, NIR_FALSE, mem_ctx,
+ if_condition);
+ progress = true;
+ }
+
+ return progress;
+}
+
+static bool
+opt_if_evaluate_condition_use(nir_if *nif, void *mem_ctx)
+{
+ bool progress = false;
+
+ /* Evaluate any uses of the if condition inside the if branches */
+ assert(nif->condition.is_ssa);
+ nir_foreach_use_safe(use_src, nif->condition.ssa) {
+ progress |= evaluate_condition_use(nif, use_src, mem_ctx, false);
+ }
+
+ nir_foreach_if_use_safe(use_src, nif->condition.ssa) {
+ if (use_src->parent_if != nif)
+ progress |= evaluate_condition_use(nif, use_src, mem_ctx, true);
+ }
+
+ return progress;
+}
+
static bool
opt_if_cf_list(nir_builder *b, struct exec_list *cf_list)
{
@@ -402,6 +494,41 @@ opt_if_cf_list(nir_builder *b, struct exec_list *cf_list)
return progress;
}
+/**
+ * These optimisations depend on nir_metadata_block_index and therefore must
+ * not do anything to cause the metadata to become invalid.
+ */
+static bool
+opt_if_safe_cf_list(nir_builder *b, struct exec_list *cf_list, void *mem_ctx)
+{
+ bool progress = false;
+ foreach_list_typed(nir_cf_node, cf_node, node, cf_list) {
+ switch (cf_node->type) {
+ case nir_cf_node_block:
+ break;
+
+ case nir_cf_node_if: {
+ nir_if *nif = nir_cf_node_as_if(cf_node);
+ progress |= opt_if_safe_cf_list(b, &nif->then_list, mem_ctx);
+ progress |= opt_if_safe_cf_list(b, &nif->else_list, mem_ctx);
+ progress |= opt_if_evaluate_condition_use(nif, mem_ctx);
+ break;
+ }
+
+ case nir_cf_node_loop: {
+ nir_loop *loop = nir_cf_node_as_loop(cf_node);
+ progress |= opt_if_safe_cf_list(b, &loop->body, mem_ctx);
+ break;
+ }
+
+ case nir_cf_node_function:
+ unreachable("Invalid cf type");
+ }
+ }
+
+ return progress;
+}
+
bool
nir_opt_if(nir_shader *shader)
{
@@ -414,6 +541,14 @@ nir_opt_if(nir_shader *shader)
nir_builder b;
nir_builder_init(&b, function->impl);
+ void *mem_ctx = ralloc_parent(function->impl);
+
+ nir_metadata_require(function->impl, nir_metadata_block_index |
+ nir_metadata_dominance);
+ progress = opt_if_safe_cf_list(&b, &function->impl->body, mem_ctx);
+ nir_metadata_preserve(function->impl, nir_metadata_block_index |
+ nir_metadata_dominance);
+
if (opt_if_cf_list(&b, &function->impl->body)) {
nir_metadata_preserve(function->impl, nir_metadata_none);
--
2.17.1
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