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Create dummy_{source,sink} lazily. #110520

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Create dummy_{source,sink} lazily. #110520

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12 changes: 8 additions & 4 deletions compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -692,8 +692,10 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
// (dummy_sink). In `dummy -> a -> b -> dummy`, using one
// dummy node leads one to think (erroneously) there exists a
// path from `b` to `a`. Two dummy nodes sidesteps the issue.
let dummy_source = graph.add_node(());
let dummy_sink = graph.add_node(());
// Construct them lazily because they're rarely needed and this
// code is hot enough for that to matter.
let mut dummy_source = None;
let mut dummy_sink = None;

for constraint in self.data.constraints.keys() {
match *constraint {
Expand All @@ -705,10 +707,12 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
);
}
Constraint::RegSubVar(_, b_id) => {
graph.add_edge(dummy_source, NodeIndex(b_id.index() as usize), *constraint);
let d = dummy_source.get_or_insert_with(|| graph.add_node(()));
graph.add_edge(*d, NodeIndex(b_id.index() as usize), *constraint);
}
Constraint::VarSubReg(a_id, _) => {
graph.add_edge(NodeIndex(a_id.index() as usize), dummy_sink, *constraint);
let d = dummy_sink.get_or_insert_with(|| graph.add_node(()));
graph.add_edge(NodeIndex(a_id.index() as usize), *d, *constraint);
}
Constraint::RegSubReg(..) => {
// this would be an edge from `dummy_source` to
Expand Down