Since we know what side of the branch we ended up on we can just
replace the use with a constant.
All helped shaders are from Unreal Engine 4 besides one shader from
Dirt Showdown.
V2: make sure we do evaluation when condition is used in else with
a single block (we were checking for blocks < the last else
block rather than <=)
shader-db results SKL:
total instructions in shared programs: 13219725 -> 13219643 (<.01%)
instructions in affected programs: 28917 -> 28835 (-0.28%)
helped: 45
HURT: 0
total cycles in shared programs: 529335971 -> 529334604 (<.01%)
cycles in affected programs: 216209 -> 214842 (-0.63%)
helped: 45
HURT: 4
Cc: Ian Romanick <i...@freedesktop.org>
fix if condition eval for else with a single block
---
src/compiler/nir/nir_opt_if.c | 121 ++++++++++++++++++++++++++++++++++
1 file changed, 121 insertions(+)
diff --git a/src/compiler/nir/nir_opt_if.c b/src/compiler/nir/nir_opt_if.c
index a52de120ad6..4ed919887ce 100644
--- a/src/compiler/nir/nir_opt_if.c
+++ b/src/compiler/nir/nir_opt_if.c
@@ -348,6 +348,86 @@ 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_before_block(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 *first_then = nir_if_first_then_block(nif);
+ if (use_src->parent_instr->block->index > first_then->index) {
+ nir_block *first_else = nir_if_first_else_block(nif);
+ if (use_src->parent_instr->block->index < first_else->index) {
+ replace_if_condition_use_with_const(use_src, NIR_TRUE, mem_ctx,
+ if_condition);
+
+ progress = true;
+ } else if (use_src->parent_instr->block->index <=
+ nir_if_last_else_block(nif)->index) {
+ 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)
{
@@ -381,6 +461,41 @@ 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)
{
@@ -393,6 +508,12 @@ 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);
+ progress = opt_if_safe_cf_list(&b, &function->impl->body, mem_ctx);
+ nir_metadata_preserve(function->impl, nir_metadata_block_index);
+
if (opt_if_cf_list(&b, &function->impl->body)) {
nir_metadata_preserve(function->impl, nir_metadata_none);
--
2.17.1
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