This is mostly thanks to Connor. The idea is to do a depth-first search
that computes pre and post indices for all the blocks. We can then figure
out if one block dominates another in constant time by two simple
comparison operations.
---
src/glsl/nir/nir.h | 9 +++++++++
src/glsl/nir/nir_dominance.c | 27 +++++++++++++++++++++++++++
2 files changed, 36 insertions(+)
diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
index 886dcd2..5d84343 100644
--- a/src/glsl/nir/nir.h
+++ b/src/glsl/nir/nir.h
@@ -1135,6 +1135,14 @@ typedef struct nir_block {
/* Set of nir_block's on the dominance frontier of this block */
struct set *dom_frontier;
+ /*
+ * These two indices have the property that dom_{pre,post}_index for each
+ * child of this block in the dominance tree will always be between
+ * dom_pre_index and dom_post_index for this block, which makes testing if
+ * a given block is dominated by another block an O(1) operation.
+ */
+ unsigned dom_pre_index, dom_post_index;
+
/* live in and out for this block; used for liveness analysis */
BITSET_WORD *live_in;
BITSET_WORD *live_out;
@@ -1501,6 +1509,7 @@ void nir_calc_dominance_impl(nir_function_impl *impl);
void nir_calc_dominance(nir_shader *shader);
nir_block *nir_dominance_lca(nir_block *b1, nir_block *b2);
+bool nir_block_dominates(nir_block *parent, nir_block *child);
void nir_dump_dom_tree_impl(nir_function_impl *impl, FILE *fp);
void nir_dump_dom_tree(nir_shader *shader, FILE *fp);
diff --git a/src/glsl/nir/nir_dominance.c b/src/glsl/nir/nir_dominance.c
index 1022692..76508f5 100644
--- a/src/glsl/nir/nir_dominance.c
+++ b/src/glsl/nir/nir_dominance.c
@@ -177,6 +177,17 @@ calc_dom_children(nir_function_impl* impl)
nir_foreach_block(impl, block_add_child, NULL);
}
+static void
+calc_dfs_indicies(nir_block *block, unsigned *index)
+{
+ block->dom_pre_index = (*index)++;
+
+ for (unsigned i = 0; i < block->num_dom_children; i++)
+ calc_dfs_indicies(block->dom_children[i], index);
+
+ block->dom_post_index = (*index)++;
+}
+
void
nir_calc_dominance_impl(nir_function_impl *impl)
{
@@ -201,6 +212,9 @@ nir_calc_dominance_impl(nir_function_impl *impl)
impl->start_block->imm_dom = NULL;
calc_dom_children(impl);
+
+ unsigned dfs_index = 0;
+ calc_dfs_indicies(impl->start_block, &dfs_index);
}
void
@@ -224,6 +238,19 @@ nir_dominance_lca(nir_block *b1, nir_block *b2)
return intersect(b1, b2);
}
+bool
+nir_block_dominates(nir_block *parent, nir_block *child)
+{
+ assert(nir_cf_node_get_function(&parent->cf_node) ==
+ nir_cf_node_get_function(&child->cf_node));
+
+ assert(nir_cf_node_get_function(&parent->cf_node)->valid_metadata &
+ nir_metadata_dominance);
+
+ return child->dom_pre_index >= parent->dom_pre_index &&
+ child->dom_pre_index <= parent->dom_post_index;
+}
+
static bool
dump_block_dom(nir_block *block, void *state)
{
--
2.2.2
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