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Use Vec::with_capacity(1) in a couple of places. #50762

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Use Vec::with_capacity(1) in a couple of places. #50762

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5 changes: 3 additions & 2 deletions src/librustc/middle/dataflow.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -181,7 +181,7 @@ fn build_local_id_to_index(body: Option<&hir::Body>,

cfg.graph.each_node(|node_idx, node| {
if let cfg::CFGNodeData::AST(id) = node.data {
index.entry(id).or_insert(vec![]).push(node_idx);
index.entry(id).or_insert_with(|| Vec::with_capacity(1)).push(node_idx);
}
true
});
Expand Down Expand Up @@ -209,7 +209,8 @@ fn build_local_id_to_index(body: Option<&hir::Body>,
}

fn visit_pat(&mut self, p: &hir::Pat) {
self.index.entry(p.hir_id.local_id).or_insert(vec![]).push(self.entry);
self.index.entry(p.hir_id.local_id)
.or_insert_with(|| Vec::with_capacity(1)).push(self.entry);
intravisit::walk_pat(self, p)
}
}
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6 changes: 5 additions & 1 deletion src/librustc/traits/project.rs
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Expand Up @@ -597,7 +597,11 @@ fn opt_normalize_projection_type<'a, 'b, 'gcx, 'tcx>(
// can ignore the `obligations` from that point on.
if !infcx.any_unresolved_type_vars(&ty.value) {
infcx.projection_cache.borrow_mut().complete(cache_key);
ty.obligations = vec![];
// Use with_capacity(1) because
// push_paranoid_cache_value_obligation() will push one
// element, and then usually no more elements are pushed.
// (Vec::new() + push() gives a capacity of 4.)
ty.obligations = Vec::with_capacity(1);
}

push_paranoid_cache_value_obligation(infcx,
Expand Down