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util: Replace recursive DFS with iterative implementation

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Doesn't fix, but improves the situation in issue #5163. The
VK.spirv_assembly.instruction.graphics.spirv_ids_abuse.lots_ids_* tests
emit about 160k instructions. ir3_sched blows out the stack after
dag_traverse_bottom_up_node reaches a depth of about 130k frames.

This patch replaces the recursively-implemented post-order traversal
with an iterative implementation using a stack, allowing us to process
DAGs as large as memory can hold.

Definitely makes you appreciate the elegance of recursion...

Reviewed-by: Emma Anholt <emma@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12232>
This commit is contained in:
Matt Turner 2021-08-04 18:47:02 -07:00 • committed by Marge Bot
parent 9261a02028
commit dcf1d8d7a4
1 changed files with 43 additions and 5 deletions
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48
src/util/dag.c
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@ -111,12 +111,50 @@ dag_traverse_bottom_up_node(struct dag_node *node,
if (_mesa_set_search(state->seen, node))
return;
util_dynarray_foreach(&node->edges, struct dag_edge, edge) {
dag_traverse_bottom_up_node(edge->child, cb, state);
}
struct util_dynarray stack;
util_dynarray_init(&stack, NULL);
cb(node, state->data);
_mesa_set_add(state->seen, node);
do {
assert(node);
while (node->edges.size != 0) {
util_dynarray_append(&stack, struct dag_node *, node);
/* Push unprocessed children onto stack in reverse order. Note that
* it's possible for any of the children nodes to already be on the
* stack.
*/
util_dynarray_foreach_reverse(&node->edges, struct dag_edge, edge) {
if (!_mesa_set_search(state->seen, edge->child)) {
util_dynarray_append(&stack, struct dag_node *, edge->child);
}
}
/* Get last element pushed: either left-most child or current node.
* If it's the current node, that means that we've processed all its
* children already.
*/
struct dag_node *top = util_dynarray_pop(&stack, struct dag_node *);
if (top == node)
break;
node = top;
}
/* Process the node */
cb(node, state->data);
_mesa_set_add(state->seen, node);
/* Find the next unprocessed node in the stack */
do {
node = NULL;
if (stack.size == 0)
break;
node = util_dynarray_pop(&stack, struct dag_node *);
} while (_mesa_set_search(state->seen, node));
} while (node);
util_dynarray_fini(&stack);
}
/**