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.

5 files changed, 12 insertions, 123 deletions

diff --git a/src/librustc/infer/higher_ranked/mod.rs b/src/librustc/infer/higher_ranked/mod.rs
index b8437e39ddc..acd5c44c1a4 100644
--- a/src/librustc/infer/higher_ranked/mod.rs
+++ b/src/librustc/infer/higher_ranked/mod.rs
@@ -19,10 +19,10 @@ use super::{CombinedSnapshot,
 use super::combine::CombineFields;
 use super::region_constraints::{TaintDirections};
 
-use rustc_data_structures::lazy_btree_map::LazyBTreeMap;
 use ty::{self, TyCtxt, Binder, TypeFoldable};
 use ty::error::TypeError;
 use ty::relate::{Relate, RelateResult, TypeRelation};
+use std::collections::BTreeMap;
 use syntax_pos::Span;
 use util::nodemap::{FxHashMap, FxHashSet};
 
@@ -247,8 +247,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
                                              snapshot: &CombinedSnapshot<'a, 'tcx>,
                                              debruijn: ty::DebruijnIndex,
                                              new_vars: &[ty::RegionVid],
-                                             a_map: &LazyBTreeMap<ty::BoundRegion,
-                                                                  ty::Region<'tcx>>,
+                                             a_map: &BTreeMap<ty::BoundRegion, ty::Region<'tcx>>,
                                              r0: ty::Region<'tcx>)
                                              -> ty::Region<'tcx> {
             // Regions that pre-dated the LUB computation stay as they are.
@@ -344,8 +343,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
                                              snapshot: &CombinedSnapshot<'a, 'tcx>,
                                              debruijn: ty::DebruijnIndex,
                                              new_vars: &[ty::RegionVid],
-                                             a_map: &LazyBTreeMap<ty::BoundRegion,
-                                                                  ty::Region<'tcx>>,
+                                             a_map: &BTreeMap<ty::BoundRegion, ty::Region<'tcx>>,
                                              a_vars: &[ty::RegionVid],
                                              b_vars: &[ty::RegionVid],
                                              r0: ty::Region<'tcx>)
@@ -414,7 +412,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
 
         fn rev_lookup<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
                                       span: Span,
-                                      a_map: &LazyBTreeMap<ty::BoundRegion, ty::Region<'tcx>>,
+                                      a_map: &BTreeMap<ty::BoundRegion, ty::Region<'tcx>>,
                                       r: ty::Region<'tcx>) -> ty::Region<'tcx>
         {
             for (a_br, a_r) in a_map {
@@ -437,7 +435,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
 }
 
 fn var_ids<'a, 'gcx, 'tcx>(fields: &CombineFields<'a, 'gcx, 'tcx>,
-                           map: &LazyBTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
+                           map: &BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
                            -> Vec<ty::RegionVid> {
     map.iter()
        .map(|(_, &r)| match *r {
diff --git a/src/librustc/infer/mod.rs b/src/librustc/infer/mod.rs
index c62e7f8d9b6..b72a25dec27 100644
--- a/src/librustc/infer/mod.rs
+++ b/src/librustc/infer/mod.rs
@@ -28,9 +28,9 @@ use ty::error::{ExpectedFound, TypeError, UnconstrainedNumeric};
 use ty::fold::TypeFoldable;
 use ty::relate::RelateResult;
 use traits::{self, ObligationCause, PredicateObligations};
-use rustc_data_structures::lazy_btree_map::LazyBTreeMap;
 use rustc_data_structures::unify as ut;
 use std::cell::{Cell, RefCell, Ref, RefMut};
+use std::collections::BTreeMap;
 use std::fmt;
 use syntax::ast;
 use errors::DiagnosticBuilder;
@@ -198,7 +198,7 @@ pub struct InferCtxt<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 
 /// A map returned by `skolemize_late_bound_regions()` indicating the skolemized
 /// region that each late-bound region was replaced with.
-pub type SkolemizationMap<'tcx> = LazyBTreeMap<ty::BoundRegion, ty::Region<'tcx>>;
+pub type SkolemizationMap<'tcx> = BTreeMap<ty::BoundRegion, ty::Region<'tcx>>;
 
 /// See `error_reporting` module for more details
 #[derive(Clone, Debug)]
@@ -1236,7 +1236,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         span: Span,
         lbrct: LateBoundRegionConversionTime,
         value: &ty::Binder<T>)
-        -> (T, LazyBTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
+        -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
         where T : TypeFoldable<'tcx>
     {
         self.tcx.replace_late_bound_regions(
diff --git a/src/librustc/ty/fold.rs b/src/librustc/ty/fold.rs
index 1793b5e1edb..42adc82f48e 100644
--- a/src/librustc/ty/fold.rs
+++ b/src/librustc/ty/fold.rs
@@ -43,7 +43,7 @@ use middle::const_val::ConstVal;
 use hir::def_id::DefId;
 use ty::{self, Binder, Ty, TyCtxt, TypeFlags};
 
-use rustc_data_structures::lazy_btree_map::LazyBTreeMap;
+use std::collections::BTreeMap;
 use std::fmt;
 use util::nodemap::FxHashSet;
 
@@ -328,7 +328,7 @@ struct RegionReplacer<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     tcx: TyCtxt<'a, 'gcx, 'tcx>,
     current_depth: u32,
     fld_r: &'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a),
-    map: LazyBTreeMap<ty::BoundRegion, ty::Region<'tcx>>
+    map: BTreeMap<ty::BoundRegion, ty::Region<'tcx>>
 }
 
 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
@@ -343,7 +343,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     pub fn replace_late_bound_regions<T,F>(self,
         value: &Binder<T>,
         mut f: F)
-        -> (T, LazyBTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
+        -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
         where F : FnMut(ty::BoundRegion) -> ty::Region<'tcx>,
               T : TypeFoldable<'tcx>,
     {
@@ -456,7 +456,7 @@ impl<'a, 'gcx, 'tcx> RegionReplacer<'a, 'gcx, 'tcx> {
             tcx,
             current_depth: 1,
             fld_r,
-            map: LazyBTreeMap::default()
+            map: BTreeMap::default()
         }
     }
 }
diff --git a/src/librustc_data_structures/lazy_btree_map.rs b/src/librustc_data_structures/lazy_btree_map.rs
deleted file mode 100644
index 74f91af10fe..00000000000
--- a/src/librustc_data_structures/lazy_btree_map.rs
+++ /dev/null
@@ -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())
-    }
-}
-
diff --git a/src/librustc_data_structures/lib.rs b/src/librustc_data_structures/lib.rs
index b2e7450e76c..5bac1bd9a7b 100644
--- a/src/librustc_data_structures/lib.rs
+++ b/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;