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use super::{DropRangesBuilder, PostOrderId};
use rustc_index::{bit_set::BitSet, vec::IndexVec};
use std::collections::BTreeMap;
impl DropRangesBuilder {
pub fn propagate_to_fixpoint(&mut self) {
trace!("before fixpoint: {:#?}", self);
let preds = self.compute_predecessors();
trace!("predecessors: {:#?}", preds.iter_enumerated().collect::<BTreeMap<_, _>>());
let mut new_state = BitSet::new_empty(self.num_values());
let mut changed_nodes = BitSet::new_empty(self.nodes.len());
let mut unchanged_mask = BitSet::new_filled(self.nodes.len());
changed_nodes.insert(0u32.into());
let mut propagate = || {
let mut changed = false;
unchanged_mask.insert_all();
for id in self.nodes.indices() {
trace!("processing {:?}, changed_nodes: {:?}", id, changed_nodes);
// Check if any predecessor has changed, and if not then short-circuit.
//
// We handle the start node specially, since it doesn't have any predecessors,
// but we need to start somewhere.
if match id.index() {
0 => !changed_nodes.contains(id),
_ => !preds[id].iter().any(|pred| changed_nodes.contains(*pred)),
} {
trace!("short-circuiting because none of {:?} have changed", preds[id]);
unchanged_mask.remove(id);
continue;
}
if id.index() == 0 {
new_state.clear();
} else {
// If we are not the start node and we have no predecessors, treat
// everything as dropped because there's no way to get here anyway.
new_state.insert_all();
};
for pred in &preds[id] {
new_state.intersect(&self.nodes[*pred].drop_state);
}
for drop in &self.nodes[id].drops {
new_state.insert(*drop);
}
for reinit in &self.nodes[id].reinits {
new_state.remove(*reinit);
}
if self.nodes[id].drop_state.intersect(&new_state) {
changed_nodes.insert(id);
changed = true;
} else {
unchanged_mask.remove(id);
}
}
changed_nodes.intersect(&unchanged_mask);
changed
};
while propagate() {
trace!("drop_state changed, re-running propagation");
}
trace!("after fixpoint: {:#?}", self);
}
fn compute_predecessors(&self) -> IndexVec<PostOrderId, Vec<PostOrderId>> {
let mut preds = IndexVec::from_fn_n(|_| vec![], self.nodes.len());
for (id, node) in self.nodes.iter_enumerated() {
// If the node has no explicit successors, we assume that control
// will from this node into the next one.
//
// If there are successors listed, then we assume that all
// possible successors are given and we do not include the default.
if node.successors.len() == 0 && id.index() != self.nodes.len() - 1 {
preds[id + 1].push(id);
} else {
for succ in &node.successors {
preds[*succ].push(id);
}
}
}
preds
}
}
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