From 259ae181391933040389e7e4206e792ad66b1487 Mon Sep 17 00:00:00 2001 From: Nicholas Nethercote Date: Tue, 24 Apr 2018 13:22:41 +1000 Subject: [PATCH] Implement LazyBTreeMap and use it in a few places. This is a thin wrapper around BTreeMap that avoids allocating upon creation. It speeds up some rustc-perf benchmarks by up to 3.6%. --- src/librustc/infer/higher_ranked/mod.rs | 12 +- src/librustc/infer/mod.rs | 6 +- src/librustc/ty/fold.rs | 8 +- .../lazy_btree_map.rs | 108 ++++++++++++++++++ src/librustc_data_structures/lib.rs | 1 + 5 files changed, 123 insertions(+), 12 deletions(-) create mode 100644 src/librustc_data_structures/lazy_btree_map.rs diff --git a/src/librustc/infer/higher_ranked/mod.rs b/src/librustc/infer/higher_ranked/mod.rs index d44f2ec95492f..a8555a3458f6b 100644 --- a/src/librustc/infer/higher_ranked/mod.rs +++ b/src/librustc/infer/higher_ranked/mod.rs @@ -19,7 +19,7 @@ use super::{CombinedSnapshot, use super::combine::CombineFields; use super::region_constraints::{TaintDirections}; -use std::collections::BTreeMap; +use rustc_data_structures::lazy_btree_map::LazyBTreeMap; use ty::{self, TyCtxt, Binder, TypeFoldable}; use ty::error::TypeError; use ty::relate::{Relate, RelateResult, TypeRelation}; @@ -247,7 +247,8 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> { snapshot: &CombinedSnapshot<'a, 'tcx>, debruijn: ty::DebruijnIndex, new_vars: &[ty::RegionVid], - a_map: &BTreeMap>, + a_map: &LazyBTreeMap>, r0: ty::Region<'tcx>) -> ty::Region<'tcx> { // Regions that pre-dated the LUB computation stay as they are. @@ -343,7 +344,8 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> { snapshot: &CombinedSnapshot<'a, 'tcx>, debruijn: ty::DebruijnIndex, new_vars: &[ty::RegionVid], - a_map: &BTreeMap>, + a_map: &LazyBTreeMap>, a_vars: &[ty::RegionVid], b_vars: &[ty::RegionVid], r0: ty::Region<'tcx>) @@ -412,7 +414,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> { fn rev_lookup<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>, span: Span, - a_map: &BTreeMap>, + a_map: &LazyBTreeMap>, r: ty::Region<'tcx>) -> ty::Region<'tcx> { for (a_br, a_r) in a_map { @@ -435,7 +437,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> { } fn var_ids<'a, 'gcx, 'tcx>(fields: &CombineFields<'a, 'gcx, 'tcx>, - map: &BTreeMap>) + map: &LazyBTreeMap>) -> Vec { map.iter() .map(|(_, &r)| match *r { diff --git a/src/librustc/infer/mod.rs b/src/librustc/infer/mod.rs index 40cc43c3ca670..553926dba8f98 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; @@ -187,7 +187,7 @@ 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> = BTreeMap>; +pub type SkolemizationMap<'tcx> = LazyBTreeMap>; /// See `error_reporting` module for more details #[derive(Clone, Debug)] @@ -1216,7 +1216,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> { span: Span, lbrct: LateBoundRegionConversionTime, value: &ty::Binder) - -> (T, BTreeMap>) + -> (T, LazyBTreeMap>) 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 8071cd0c639da..80bdc4f89df85 100644 --- a/src/librustc/ty/fold.rs +++ b/src/librustc/ty/fold.rs @@ -43,8 +43,8 @@ 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::fmt; -use std::collections::BTreeMap; use util::nodemap::FxHashSet; /// The TypeFoldable trait is implemented for every type that can be folded. @@ -334,7 +334,7 @@ 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: BTreeMap> + map: LazyBTreeMap> } impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> { @@ -349,7 +349,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> { pub fn replace_late_bound_regions(self, value: &Binder, mut f: F) - -> (T, BTreeMap>) + -> (T, LazyBTreeMap>) where F : FnMut(ty::BoundRegion) -> ty::Region<'tcx>, T : TypeFoldable<'tcx>, { @@ -462,7 +462,7 @@ impl<'a, 'gcx, 'tcx> RegionReplacer<'a, 'gcx, 'tcx> { tcx, current_depth: 1, fld_r, - map: BTreeMap::default() + map: LazyBTreeMap::default() } } } diff --git a/src/librustc_data_structures/lazy_btree_map.rs b/src/librustc_data_structures/lazy_btree_map.rs new file mode 100644 index 0000000000000..74f91af10fe63 --- /dev/null +++ b/src/librustc_data_structures/lazy_btree_map.rs @@ -0,0 +1,108 @@ +// 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 or the MIT license +// , 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(Option>); + +impl LazyBTreeMap { + pub fn new() -> LazyBTreeMap { + LazyBTreeMap(None) + } + + pub fn iter(&self) -> Iter { + 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 LazyBTreeMap { + fn instantiate(&mut self) -> &mut BTreeMap { + 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 { + self.instantiate().insert(key, value) + } + + pub fn entry(&mut self, key: K) -> btree_map::Entry { + self.instantiate().entry(key) + } + + pub fn values<'a>(&'a self) -> Values<'a, K, V> { + Values(self.0.as_ref().map(|btm| btm.values())) + } +} + +impl Default for LazyBTreeMap { + fn default() -> LazyBTreeMap { + LazyBTreeMap::new() + } +} + +impl<'a, K: 'a, V: 'a> IntoIterator for &'a LazyBTreeMap { + 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>); + +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) { + self.0.as_ref().map_or_else(|| (0, Some(0)), |iter| iter.size_hint()) + } +} + +pub struct Values<'a, K: 'a, V: 'a>(Option>); + +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) { + 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 ba1d73dc268df..154c086614ca5 100644 --- a/src/librustc_data_structures/lib.rs +++ b/src/librustc_data_structures/lib.rs @@ -56,6 +56,7 @@ 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;