Remove LazyBTreeMap.

It was introduced in #50240 to avoid an allocation when creating a new
BTreeMap, which gave some speed-ups. But then #50352 made that the
default behaviour for BTreeMap, so LazyBTreeMap is no longer necessary.

src/librustc_data_structures/lazy_btree_map.rs

@@ -1,108 +0,0 @@
-// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-use std::collections::btree_map;
-use std::collections::BTreeMap;
-
-/// A thin wrapper around BTreeMap that avoids allocating upon creation.
-///
-/// Vec, HashSet and HashMap all have the nice feature that they don't do any
-/// heap allocation when creating a new structure of the default size. In
-/// contrast, BTreeMap *does* allocate in that situation. The compiler uses
-/// B-Tree maps in some places such that many maps are created but few are
-/// inserted into, so having a BTreeMap alternative that avoids allocating on
-/// creation is a performance win.
-///
-/// Only a fraction of BTreeMap's functionality is currently supported.
-/// Additional functionality should be added on demand.
-#[derive(Debug)]
-pub struct LazyBTreeMap<K, V>(Option<BTreeMap<K, V>>);
-
-impl<K, V> LazyBTreeMap<K, V> {
-    pub fn new() -> LazyBTreeMap<K, V> {
-        LazyBTreeMap(None)
-    }
-
-    pub fn iter(&self) -> Iter<K, V> {
-        Iter(self.0.as_ref().map(|btm| btm.iter()))
-    }
-
-    pub fn is_empty(&self) -> bool {
-        self.0.as_ref().map_or(true, |btm| btm.is_empty())
-    }
-}
-
-impl<K: Ord, V> LazyBTreeMap<K, V> {
-    fn instantiate(&mut self) -> &mut BTreeMap<K, V> {
-        if let Some(ref mut btm) = self.0 {
-            btm
-        } else {
-            let btm = BTreeMap::new();
-            self.0 = Some(btm);
-            self.0.as_mut().unwrap()
-        }
-    }
-
-    pub fn insert(&mut self, key: K, value: V) -> Option<V> {
-        self.instantiate().insert(key, value)
-    }
-
-    pub fn entry(&mut self, key: K) -> btree_map::Entry<K, V> {
-        self.instantiate().entry(key)
-    }
-
-    pub fn values<'a>(&'a self) -> Values<'a, K, V> {
-        Values(self.0.as_ref().map(|btm| btm.values()))
-    }
-}
-
-impl<K: Ord, V> Default for LazyBTreeMap<K, V> {
-    fn default() -> LazyBTreeMap<K, V> {
-        LazyBTreeMap::new()
-    }
-}
-
-impl<'a, K: 'a, V: 'a> IntoIterator for &'a LazyBTreeMap<K, V> {
-    type Item = (&'a K, &'a V);
-    type IntoIter = Iter<'a, K, V>;
-
-    fn into_iter(self) -> Iter<'a, K, V> {
-        self.iter()
-    }
-}
-
-pub struct Iter<'a, K: 'a, V: 'a>(Option<btree_map::Iter<'a, K, V>>);
-
-impl<'a, K: 'a, V: 'a> Iterator for Iter<'a, K, V> {
-    type Item = (&'a K, &'a V);
-
-    fn next(&mut self) -> Option<(&'a K, &'a V)> {
-        self.0.as_mut().and_then(|iter| iter.next())
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        self.0.as_ref().map_or_else(|| (0, Some(0)), |iter| iter.size_hint())
-    }
-}
-
-pub struct Values<'a, K: 'a, V: 'a>(Option<btree_map::Values<'a, K, V>>);
-
-impl<'a, K, V> Iterator for Values<'a, K, V> {
-    type Item = &'a V;
-
-    fn next(&mut self) -> Option<&'a V> {
-        self.0.as_mut().and_then(|values| values.next())
-    }
-
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        self.0.as_ref().map_or_else(|| (0, Some(0)), |values| values.size_hint())
-    }
-}
-

src/librustc_data_structures/lib.rs

@@ -61,7 +61,6 @@ pub mod bitvec;
 pub mod graph;
 pub mod indexed_set;
 pub mod indexed_vec;
-pub mod lazy_btree_map;
 pub mod obligation_forest;
 pub mod sip128;
 pub mod snapshot_map;