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Remove NodeState::OnDfsStack.

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It's not necessary; cycles (which are rare) can be detected by looking
at the node stack.

This change speeds things up slightly, as well as simplifying the code a
little.
This commit is contained in:
Nicholas Nethercote 2019-09-24 13:25:29 +10:00
parent 06c68947ad
commit 3b506d9694
1 changed files with 19 additions and 19 deletions
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38
src/librustc_data_structures/obligation_forest/mod.rs
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@ -235,10 +235,6 @@ enum NodeState {
/// This obligation was resolved to an error. Error nodes are
/// removed from the vector by the compression step.
Error,
/// This is a temporary state used in DFS loops to detect cycles,
/// it should not exist outside of these DFSes.
OnDfsStack,
}
#[derive(Debug)]
@ -491,7 +487,6 @@ impl<O: ForestObligation> ObligationForest<O> {
NodeState::Pending => {},
NodeState::Success => self.find_cycles_from_node(&mut stack, processor, index),
NodeState::Waiting | NodeState::Done | NodeState::Error => {},
NodeState::OnDfsStack => self.find_cycles_from_node(&mut stack, processor, index),
}
}
@ -506,20 +501,25 @@ impl<O: ForestObligation> ObligationForest<O> {
{
let node = &self.nodes[index];
match node.state.get() {
NodeState::OnDfsStack => {
let rpos = stack.iter().rposition(|&n| n == index).unwrap();
processor.process_backedge(stack[rpos..].iter().map(GetObligation(&self.nodes)),
PhantomData);
}
NodeState::Success => {
node.state.set(NodeState::OnDfsStack);
stack.push(index);
for &index in node.dependents.iter() {
self.find_cycles_from_node(stack, processor, index);
match stack.iter().rposition(|&n| n == index) {
None => {
stack.push(index);
for &index in node.dependents.iter() {
self.find_cycles_from_node(stack, processor, index);
}
stack.pop();
node.state.set(NodeState::Done);
}
Some(rpos) => {
// Cycle detected.
processor.process_backedge(
stack[rpos..].iter().map(GetObligation(&self.nodes)),
PhantomData
);
}
}
stack.pop();
node.state.set(NodeState::Done);
},
}
NodeState::Waiting | NodeState::Pending => {
// This node is still reachable from some pending node. We
// will get to it when they are all processed.
@ -598,7 +598,7 @@ impl<O: ForestObligation> ObligationForest<O> {
fn mark_as_waiting_from(&self, node: &Node<O>) {
match node.state.get() {
NodeState::Waiting | NodeState::Error | NodeState::OnDfsStack => return,
NodeState::Waiting | NodeState::Error => return,
NodeState::Success => node.state.set(NodeState::Waiting),
NodeState::Pending | NodeState::Done => {},
}
@ -659,7 +659,7 @@ impl<O: ForestObligation> ObligationForest<O> {
dead_nodes += 1;
self.insert_into_error_cache(index);
}
NodeState::OnDfsStack | NodeState::Success => unreachable!()
NodeState::Success => unreachable!()
}
}