From: Connor Abbott <cwabbo...@gmail.com>
v2: use nir_cf_node_remove_after().
v2: use foreach_list_typed() instead of hardcoding a list walk.
v3: update to new control flow modification helpers.
Signed-off-by: Connor Abbott <connor.w.abb...@intel.com>
---
src/glsl/nir/nir_opt_dead_cf.c | 123 ++++++++++++++++++++++++++++++++++++++---
1 file changed, 115 insertions(+), 8 deletions(-)
diff --git a/src/glsl/nir/nir_opt_dead_cf.c b/src/glsl/nir/nir_opt_dead_cf.c
index fca842c..66961ce 100644
--- a/src/glsl/nir/nir_opt_dead_cf.c
+++ b/src/glsl/nir/nir_opt_dead_cf.c
@@ -40,6 +40,26 @@
* We delete the if statement and paste the contents of the always-executed
* branch into the surrounding control flow, possibly removing more code if
* the branch had a jump at the end.
+ *
+ * The other way is that control flow can end in a jump so that code after it
+ * never gets executed. In particular, this can happen after optimizing
+ * something like:
+ *
+ * if (true) {
+ * ...
+ * break;
+ * }
+ * ...
+ *
+ * We also consider the case where both branches of an if end in a jump, e.g.:
+ *
+ * if (...) {
+ * break;
+ * } else {
+ * continue;
+ * }
+ * ...
+ *
*/
static void
@@ -111,30 +131,117 @@ opt_constant_if(nir_if *if_stmt, bool condition)
}
static bool
-dead_cf_cb(nir_block *block, void *state)
+dead_cf_block(nir_block *block)
{
- bool *progress = state;
-
nir_if *following_if = nir_block_get_following_if(block);
if (!following_if)
- return true;
+ return false;
nir_const_value *const_value =
nir_src_as_const_value(following_if->condition);
if (!const_value)
- return true;
+ return false;
opt_constant_if(following_if, const_value->u[0] != 0);
- *progress = true;
return true;
}
static bool
-opt_dead_cf_impl(nir_function_impl *impl)
+ends_in_jump(nir_block *block)
+{
+ if (exec_list_is_empty(&block->instr_list))
+ return false;
+
+ nir_instr *instr = nir_block_last_instr(block);
+ return instr->type == nir_instr_type_jump;
+}
+
+static bool
+dead_cf_list(struct exec_list *list, bool *list_ends_in_jump)
{
bool progress = false;
- nir_foreach_block(impl, dead_cf_cb, &progress);
+ *list_ends_in_jump = false;
+
+ nir_cf_node *prev = NULL;
+
+ foreach_list_typed(nir_cf_node, cur, node, list) {
+ switch (cur->type) {
+ case nir_cf_node_block: {
+ nir_block *block = nir_cf_node_as_block(cur);
+ if (dead_cf_block(block)) {
+ /* We just deleted the if after this block, so we may have
+ * deleted the block before or after it -- which one is an
+ * implementation detail. Therefore, to recover the place we were
+ * at, we have to use the previous cf_node.
+ */
+
+ if (prev) {
+ cur = nir_cf_node_next(prev);
+ } else {
+ cur = exec_node_data(nir_cf_node, exec_list_get_head(list),
+ node);
+ }
+
+ block = nir_cf_node_as_block(cur);
+
+ progress = true;
+ }
+
+ if (ends_in_jump(block)) {
+ *list_ends_in_jump = true;
+
+ if (!exec_node_is_tail_sentinel(cur->node.next)) {
+ remove_after_cf_node(cur);
+ return true;
+ }
+ }
+
+ break;
+ }
+
+ case nir_cf_node_if: {
+ nir_if *if_stmt = nir_cf_node_as_if(cur);
+ bool then_ends_in_jump, else_ends_in_jump;
+ progress |= dead_cf_list(&if_stmt->then_list, &then_ends_in_jump);
+ progress |= dead_cf_list(&if_stmt->else_list, &else_ends_in_jump);
+
+ if (then_ends_in_jump && else_ends_in_jump) {
+ *list_ends_in_jump = true;
+ nir_block *next = nir_cf_node_as_block(nir_cf_node_next(cur));
+ if (!exec_list_is_empty(&next->instr_list) ||
+ !exec_node_is_tail_sentinel(next->cf_node.node.next)) {
+ remove_after_cf_node(cur);
+ return true;
+ }
+ }
+
+ break;
+ }
+
+ case nir_cf_node_loop: {
+ nir_loop *loop = nir_cf_node_as_loop(cur);
+ bool dummy;
+ progress |= dead_cf_list(&loop->body, &dummy);
+
+ break;
+ }
+
+ default:
+ unreachable("unknown cf node type");
+ }
+
+ prev = cur;
+ }
+
+ return progress;
+}
+
+static bool
+opt_dead_cf_impl(nir_function_impl *impl)
+{
+ bool dummy;
+ bool progress = dead_cf_list(&impl->body, &dummy);
if (progress)
nir_metadata_preserve(impl, nir_metadata_none);
--
2.4.3
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