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Auto merge of #78607 - HeroicKatora:post-order-walk-iter, r=davidtwco

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Transform post order walk to an iterative approach

The previous recursive approach might overflow the stack when walking a
particularly deep, list-like, graph. In particular, dominator
calculation for borrow checking does such a traversal and very long
functions might lead to a region dependency graph with in this
problematic structure.

This addresses what appears to be the cause of #78567 (`@SunHao-0` thanks for the stack trace).
This commit is contained in:
bors 2020-11-02 16:01:10 +00:00
commit 338f939a8d
1 changed files with 20 additions and 5 deletions
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25
compiler/rustc_data_structures/src/graph/iterate/mod.rs
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@ -33,16 +33,31 @@ fn post_order_walk<G: DirectedGraph + WithSuccessors + WithNumNodes>(
result: &mut Vec<G::Node>,
visited: &mut IndexVec<G::Node, bool>,
) {
struct PostOrderFrame<Node, Iter> {
node: Node,
iter: Iter,
}
if visited[node] {
return;
}
visited[node] = true;
for successor in graph.successors(node) {
post_order_walk(graph, successor, result, visited);
let mut stack = vec![PostOrderFrame { node, iter: graph.successors(node) }];
'recurse: while let Some(frame) = stack.last_mut() {
let node = frame.node;
visited[node] = true;
while let Some(successor) = frame.iter.next() {
if !visited[successor] {
stack.push(PostOrderFrame { node: successor, iter: graph.successors(successor) });
continue 'recurse;
}
}
let _ = stack.pop();
result.push(node);
}
result.push(node);
}
pub fn reverse_post_order<G: DirectedGraph + WithSuccessors + WithNumNodes>(