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
v4:
- create some helpers as suggested by Jason.
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.h | 22 +++++++
src/compiler/nir/nir_opt_if.c | 113 ++++++++++++++++++++++++++++++++++
2 files changed, 135 insertions(+)
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index 009a6d60371..0caacd30173 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -2331,6 +2331,28 @@ nir_after_block_before_jump(nir_block *block)
}
}
+static inline nir_cursor
+nir_before_src(nir_src *src, bool is_if_condition)
+{
+ if (is_if_condition) {
+ nir_block *prev_block =
+ nir_cf_node_as_block(nir_cf_node_prev(&src->parent_if->cf_node));
+ assert(!nir_block_ends_in_jump(prev_block));
+ return nir_after_block(prev_block);
+ } else if (src->parent_instr->type == nir_instr_type_phi) {
+ nir_phi_instr *cond_phi = nir_instr_as_phi(src->parent_instr);
+ nir_foreach_phi_src(phi_src, cond_phi) {
+ if (phi_src->src.ssa == src->ssa) {
+ return nir_after_block_before_jump(phi_src->pred);
+ }
+ }
+
+ unreachable("failed to find phi src");
+ } else {
+ return nir_before_instr(src->parent_instr);
+ }
+}
+
static inline nir_cursor
nir_before_cf_node(nir_cf_node *node)
{
diff --git a/src/compiler/nir/nir_opt_if.c b/src/compiler/nir/nir_opt_if.c
index dacf2d6c667..11c6693d302 100644
--- a/src/compiler/nir/nir_opt_if.c
+++ b/src/compiler/nir/nir_opt_if.c
@@ -369,6 +369,76 @@ opt_if_loop_terminator(nir_if *nif)
return true;
}
+static void
+replace_if_condition_use_with_const(nir_src *use, void *mem_ctx,
+ nir_cursor cursor, unsigned nir_boolean,
+ 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;
+ nir_instr_insert(cursor, &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_if_condition(nir_if *nif, nir_cursor cursor, uint32_t *value)
+{
+ nir_block *use_block = nir_cursor_current_block(cursor);
+ if (nir_block_dominates(nir_if_first_then_block(nif), use_block)) {
+ *value = NIR_TRUE;
+ return true;
+ } else if (nir_block_dominates(nir_if_first_else_block(nif), use_block)) {
+ *value = NIR_FALSE;
+ return true;
+ } else {
+ return false;
+ }
+}
+
+static bool
+evaluate_condition_use(nir_if *nif, nir_src *use_src, void *mem_ctx,
+ bool is_if_condition)
+{
+ bool progress = false;
+
+ uint32_t value;
+ nir_cursor cursor = nir_before_src(use_src, is_if_condition);
+ if (evaluate_if_condition(nif, cursor, &value)) {
+ replace_if_condition_use_with_const(use_src, mem_ctx, cursor, value,
+ is_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 +472,41 @@ 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 +519,14 @@ nir_opt_if(nir_shader *shader)
nir_builder b;
nir_builder_init(&b, function->impl);
+ void *mem_ctx = ralloc_parent(function->impl);
