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compiler/rust/cfg: Use DepthFirstSearch for find_back_edges()

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Reviewed-by: Lorenzo Rossi <git@rossilorenzo.dev>
Reviewed-by: Mary Guillemard <mary@mary.zone>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37536>
This commit is contained in:
Faith Ekstrand 2025-09-23 16:42:38 -04:00 • committed by Marge Bot
parent 030005a772
commit 76bba3ffba
1 changed files with 34 additions and 24 deletions
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58
src/compiler/rust/cfg.rs
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@ -200,27 +200,42 @@ fn calc_dominance<N>(nodes: &mut Vec<CFGNode<N>>) {
debug_assert!(dom_dfs.count == nodes.len() * 2);
}
fn loop_detect_dfs<N>(
nodes: &[CFGNode<N>],
id: usize,
pre: &mut BitSet,
post: &mut BitSet,
back_edges: &mut Vec<(usize, usize)>,
) {
if pre.contains(id) {
return;
struct BackEdgesDFS<'a, N> {
nodes: &'a [CFGNode<N>],
pre: BitSet,
post: BitSet,
back_edges: Vec<(usize, usize)>,
}
impl<'a, N> DepthFirstSearch for BackEdgesDFS<'a, N> {
type ChildIter = Cloned<std::slice::Iter<'a, usize>>;
fn pre(&mut self, id: usize) -> Self::ChildIter {
self.pre.insert(id);
self.nodes[id].succ.iter().cloned()
}
pre.insert(id);
for &s in nodes[id].succ.iter() {
if pre.contains(s) && !post.contains(s) {
back_edges.push((id, s));
fn edge(&mut self, parent: usize, child: usize) {
if self.pre.contains(child) && !self.post.contains(child) {
self.back_edges.push((parent, child));
}
loop_detect_dfs(nodes, s, pre, post, back_edges);
}
post.insert(id);
fn post(&mut self, id: usize) {
self.post.insert(id);
}
}
fn find_back_edges<N>(nodes: &[CFGNode<N>]) -> Vec<(usize, usize)> {
let mut be_dfs = BackEdgesDFS {
nodes,
pre: Default::default(),
post: Default::default(),
back_edges: Default::default(),
};
dfs(&mut be_dfs, 0);
be_dfs.back_edges
}
/// Computes the set of nodes that reach the given node without going through
@ -245,11 +260,7 @@ fn reaches_dfs<N>(
}
fn detect_loops<N>(nodes: &mut Vec<CFGNode<N>>) -> bool {
let mut dfs_pre = BitSet::new();
let mut dfs_post = BitSet::new();
let mut back_edges = Vec::new();
loop_detect_dfs(nodes, 0, &mut dfs_pre, &mut dfs_post, &mut back_edges);
let back_edges = find_back_edges(nodes);
if back_edges.is_empty() {
return false;
}
@ -266,9 +277,8 @@ fn detect_loops<N>(nodes: &mut Vec<CFGNode<N>>) -> bool {
loops.insert(h);
// re-use dfs_pre for our reaches set
dfs_pre.clear();
let reaches = &mut dfs_pre;
reaches_dfs(nodes, c, h, reaches);
let mut reaches = BitSet::new();
reaches_dfs(nodes, c, h, &mut reaches);
for n in reaches.iter() {
node_loops[n].insert(h);