Rollup merge of rust-lang#37229 - nnethercote:FxHasher, r=nikomatsakis

Replace FNV with a faster hash function.

Hash table lookups are very hot in rustc profiles and the time taken within `FnvHash` itself is a big part of that. Although FNV is a simple hash, it processes its input one byte at a time. In contrast, Firefox has a homespun hash function that is also simple but works on multiple bytes at a time. So I tried it out and the results are compelling:

```
futures-rs-test  4.326s vs  4.212s --> 1.027x faster (variance: 1.001x, 1.007x)
helloworld       0.233s vs  0.232s --> 1.004x faster (variance: 1.037x, 1.016x)
html5ever-2016-  5.397s vs  5.210s --> 1.036x faster (variance: 1.009x, 1.006x)
hyper.0.5.0      5.018s vs  4.905s --> 1.023x faster (variance: 1.007x, 1.006x)
inflate-0.1.0    4.889s vs  4.872s --> 1.004x faster (variance: 1.012x, 1.007x)
issue-32062-equ  0.347s vs  0.335s --> 1.035x faster (variance: 1.033x, 1.019x)
issue-32278-big  1.717s vs  1.622s --> 1.059x faster (variance: 1.027x, 1.028x)
jld-day15-parse  1.537s vs  1.459s --> 1.054x faster (variance: 1.005x, 1.003x)
piston-image-0. 11.863s vs 11.482s --> 1.033x faster (variance: 1.060x, 1.002x)
regex.0.1.30     2.517s vs  2.453s --> 1.026x faster (variance: 1.011x, 1.013x)
rust-encoding-0  2.080s vs  2.047s --> 1.016x faster (variance: 1.005x, 1.005x)
syntex-0.42.2   32.268s vs 31.275s --> 1.032x faster (variance: 1.014x, 1.022x)
syntex-0.42.2-i 17.629s vs 16.559s --> 1.065x faster (variance: 1.013x, 1.021x)
```

(That's a stage1 compiler doing debug builds. Results for a stage2 compiler are similar.)

The attached commit is not in a state suitable for landing because I changed the implementation of FnvHasher without changing its name (because that would have required touching many lines in the compiler). Nonetheless, it is a good place to start discussions.

Profiles show very clearly that this new hash function is a lot faster to compute than FNV. The quality of the new hash function is less clear -- it seems to do better in some cases and worse in others (judging by the number of instructions executed in `Hash{Map,Set}::get`).

CC @brson, @arthurprs

src/librustc/dep_graph/dep_tracking_map.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 use hir::def_id::DefId;
-use rustc_data_structures::fnv::FnvHashMap;
+use rustc_data_structures::fx::FxHashMap;
 use std::cell::RefCell;
 use std::ops::Index;
 use std::hash::Hash;
@@ -24,7 +24,7 @@ use super::{DepNode, DepGraph};
 pub struct DepTrackingMap<M: DepTrackingMapConfig> {
     phantom: PhantomData<M>,
     graph: DepGraph,
-    map: FnvHashMap<M::Key, M::Value>,
+    map: FxHashMap<M::Key, M::Value>,
 }
 
 pub trait DepTrackingMapConfig {
@@ -38,7 +38,7 @@ impl<M: DepTrackingMapConfig> DepTrackingMap<M> {
         DepTrackingMap {
             phantom: PhantomData,
             graph: graph,
-            map: FnvHashMap()
+            map: FxHashMap()
         }
     }
 

src/librustc/dep_graph/edges.rs

@@ -8,15 +8,15 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use rustc_data_structures::fnv::{FnvHashMap, FnvHashSet};
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use std::fmt::Debug;
 use std::hash::Hash;
 use super::{DepGraphQuery, DepNode};
 
 pub struct DepGraphEdges<D: Clone + Debug + Eq + Hash> {
     nodes: Vec<DepNode<D>>,
-    indices: FnvHashMap<DepNode<D>, IdIndex>,
-    edges: FnvHashSet<(IdIndex, IdIndex)>,
+    indices: FxHashMap<DepNode<D>, IdIndex>,
+    edges: FxHashSet<(IdIndex, IdIndex)>,
     open_nodes: Vec<OpenNode>,
 }
 
@@ -46,8 +46,8 @@ impl<D: Clone + Debug + Eq + Hash> DepGraphEdges<D> {
     pub fn new() -> DepGraphEdges<D> {
         DepGraphEdges {
             nodes: vec![],
-            indices: FnvHashMap(),
-            edges: FnvHashSet(),
+            indices: FxHashMap(),
+            edges: FxHashSet(),
             open_nodes: Vec::new()
         }
     }

src/librustc/dep_graph/graph.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 use hir::def_id::DefId;
-use rustc_data_structures::fnv::FnvHashMap;
+use rustc_data_structures::fx::FxHashMap;
 use session::config::OutputType;
 use std::cell::{Ref, RefCell};
 use std::rc::Rc;
@@ -34,19 +34,19 @@ struct DepGraphData {
     /// things available to us. If we find that they are not dirty, we
     /// load the path to the file storing those work-products here into
     /// this map. We can later look for and extract that data.
-    previous_work_products: RefCell<FnvHashMap<Arc<WorkProductId>, WorkProduct>>,
+    previous_work_products: RefCell<FxHashMap<Arc<WorkProductId>, WorkProduct>>,
 
     /// Work-products that we generate in this run.
-    work_products: RefCell<FnvHashMap<Arc<WorkProductId>, WorkProduct>>,
+    work_products: RefCell<FxHashMap<Arc<WorkProductId>, WorkProduct>>,
 }
 
 impl DepGraph {
     pub fn new(enabled: bool) -> DepGraph {
         DepGraph {
             data: Rc::new(DepGraphData {
                 thread: DepGraphThreadData::new(enabled),
-                previous_work_products: RefCell::new(FnvHashMap()),
-                work_products: RefCell::new(FnvHashMap()),
+                previous_work_products: RefCell::new(FxHashMap()),
+                work_products: RefCell::new(FxHashMap()),
             })
         }
     }
@@ -117,7 +117,7 @@ impl DepGraph {
 
     /// Access the map of work-products created during this run. Only
     /// used during saving of the dep-graph.
-    pub fn work_products(&self) -> Ref<FnvHashMap<Arc<WorkProductId>, WorkProduct>> {
+    pub fn work_products(&self) -> Ref<FxHashMap<Arc<WorkProductId>, WorkProduct>> {
         self.data.work_products.borrow()
     }
 }

src/librustc/dep_graph/query.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use rustc_data_structures::fnv::FnvHashMap;
+use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::graph::{Direction, INCOMING, Graph, NodeIndex, OUTGOING};
 use std::fmt::Debug;
 use std::hash::Hash;
@@ -17,15 +17,15 @@ use super::DepNode;
 
 pub struct DepGraphQuery<D: Clone + Debug + Hash + Eq> {
     pub graph: Graph<DepNode<D>, ()>,
-    pub indices: FnvHashMap<DepNode<D>, NodeIndex>,
+    pub indices: FxHashMap<DepNode<D>, NodeIndex>,
 }
 
 impl<D: Clone + Debug + Hash + Eq> DepGraphQuery<D> {
     pub fn new(nodes: &[DepNode<D>],
                edges: &[(DepNode<D>, DepNode<D>)])
                -> DepGraphQuery<D> {
         let mut graph = Graph::new();
-        let mut indices = FnvHashMap();
+        let mut indices = FxHashMap();
         for node in nodes {
             indices.insert(node.clone(), graph.next_node_index());
             graph.add_node(node.clone());

src/librustc/hir/map/definitions.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 use hir::def_id::{CrateNum, DefId, DefIndex, LOCAL_CRATE};
-use rustc_data_structures::fnv::FnvHashMap;
+use rustc_data_structures::fx::FxHashMap;
 use std::fmt::Write;
 use std::hash::{Hash, Hasher};
 use std::collections::hash_map::DefaultHasher;
@@ -22,7 +22,7 @@ use util::nodemap::NodeMap;
 #[derive(Clone)]
 pub struct Definitions {
     data: Vec<DefData>,
-    key_map: FnvHashMap<DefKey, DefIndex>,
+    key_map: FxHashMap<DefKey, DefIndex>,
     node_map: NodeMap<DefIndex>,
 }
 
@@ -219,7 +219,7 @@ impl Definitions {
     pub fn new() -> Definitions {
         Definitions {
             data: vec![],
-            key_map: FnvHashMap(),
+            key_map: FxHashMap(),
             node_map: NodeMap(),
         }
     }

src/librustc/hir/mod.rs

@@ -33,7 +33,7 @@ pub use self::PathParameters::*;
 
 use hir::def::Def;
 use hir::def_id::DefId;
-use util::nodemap::{NodeMap, FnvHashSet};
+use util::nodemap::{NodeMap, FxHashSet};
 
 use syntax_pos::{mk_sp, Span, ExpnId, DUMMY_SP};
 use syntax::codemap::{self, respan, Spanned};
@@ -1605,4 +1605,4 @@ pub type TraitMap = NodeMap<Vec<TraitCandidate>>;
 
 // Map from the NodeId of a glob import to a list of items which are actually
 // imported.
-pub type GlobMap = NodeMap<FnvHashSet<Name>>;
+pub type GlobMap = NodeMap<FxHashSet<Name>>;

src/librustc/infer/freshen.rs

@@ -32,7 +32,7 @@
 
 use ty::{self, Ty, TyCtxt, TypeFoldable};
 use ty::fold::TypeFolder;
-use util::nodemap::FnvHashMap;
+use util::nodemap::FxHashMap;
 use std::collections::hash_map::Entry;
 
 use super::InferCtxt;
@@ -41,7 +41,7 @@ use super::unify_key::ToType;
 pub struct TypeFreshener<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
     freshen_count: u32,
-    freshen_map: FnvHashMap<ty::InferTy, Ty<'tcx>>,
+    freshen_map: FxHashMap<ty::InferTy, Ty<'tcx>>,
 }
 
 impl<'a, 'gcx, 'tcx> TypeFreshener<'a, 'gcx, 'tcx> {
@@ -50,7 +50,7 @@ impl<'a, 'gcx, 'tcx> TypeFreshener<'a, 'gcx, 'tcx> {
         TypeFreshener {
             infcx: infcx,
             freshen_count: 0,
-            freshen_map: FnvHashMap(),
+            freshen_map: FxHashMap(),
         }
     }
 

src/librustc/infer/higher_ranked/mod.rs

@@ -24,7 +24,7 @@ use ty::{self, TyCtxt, Binder, TypeFoldable};
 use ty::error::TypeError;
 use ty::relate::{Relate, RelateResult, TypeRelation};
 use syntax_pos::Span;
-use util::nodemap::{FnvHashMap, FnvHashSet};
+use util::nodemap::{FxHashMap, FxHashSet};
 
 pub struct HrMatchResult<U> {
     pub value: U,
@@ -135,7 +135,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
             // Map each skolemized region to a vector of other regions that it
             // must be equated with. (Note that this vector may include other
             // skolemized regions from `skol_map`.)
-            let skol_resolution_map: FnvHashMap<_, _> =
+            let skol_resolution_map: FxHashMap<_, _> =
                 skol_map
                 .iter()
                 .map(|(&br, &skol)| {
@@ -158,7 +158,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
             // `skol_map`. There should always be a representative if things
             // are properly well-formed.
             let mut unconstrained_regions = vec![];
-            let skol_representatives: FnvHashMap<_, _> =
+            let skol_representatives: FxHashMap<_, _> =
                 skol_resolution_map
                 .iter()
                 .map(|(&skol, &(br, ref regions))| {
@@ -268,7 +268,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
                                              snapshot: &CombinedSnapshot,
                                              debruijn: ty::DebruijnIndex,
                                              new_vars: &[ty::RegionVid],
-                                             a_map: &FnvHashMap<ty::BoundRegion, &'tcx ty::Region>,
+                                             a_map: &FxHashMap<ty::BoundRegion, &'tcx ty::Region>,
                                              r0: &'tcx ty::Region)
                                              -> &'tcx ty::Region {
             // Regions that pre-dated the LUB computation stay as they are.
@@ -364,8 +364,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
                                              snapshot: &CombinedSnapshot,
                                              debruijn: ty::DebruijnIndex,
                                              new_vars: &[ty::RegionVid],
-                                             a_map: &FnvHashMap<ty::BoundRegion,
-                                                                &'tcx ty::Region>,
+                                             a_map: &FxHashMap<ty::BoundRegion, &'tcx ty::Region>,
                                              a_vars: &[ty::RegionVid],
                                              b_vars: &[ty::RegionVid],
                                              r0: &'tcx ty::Region)
@@ -434,7 +433,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
 
         fn rev_lookup<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>,
                                       span: Span,
-                                      a_map: &FnvHashMap<ty::BoundRegion, &'tcx ty::Region>,
+                                      a_map: &FxHashMap<ty::BoundRegion, &'tcx ty::Region>,
                                       r: &'tcx ty::Region) -> &'tcx ty::Region
         {
             for (a_br, a_r) in a_map {
@@ -457,7 +456,7 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
 }
 
 fn var_ids<'a, 'gcx, 'tcx>(fields: &CombineFields<'a, 'gcx, 'tcx>,
-                           map: &FnvHashMap<ty::BoundRegion, &'tcx ty::Region>)
+                           map: &FxHashMap<ty::BoundRegion, &'tcx ty::Region>)
                            -> Vec<ty::RegionVid> {
     map.iter()
        .map(|(_, &r)| match *r {
@@ -504,7 +503,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                        snapshot: &CombinedSnapshot,
                        r: &'tcx ty::Region,
                        directions: TaintDirections)
-                       -> FnvHashSet<&'tcx ty::Region> {
+                       -> FxHashSet<&'tcx ty::Region> {
         self.region_vars.tainted(&snapshot.region_vars_snapshot, r, directions)
     }
 
@@ -568,7 +567,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         let escaping_types =
             self.type_variables.borrow_mut().types_escaping_snapshot(&snapshot.type_snapshot);
 
-        let mut escaping_region_vars = FnvHashSet();
+        let mut escaping_region_vars = FxHashSet();
         for ty in &escaping_types {
             self.tcx.collect_regions(ty, &mut escaping_region_vars);
         }
@@ -764,7 +763,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         // region back to the `ty::BoundRegion` that it originally
         // represented. Because `leak_check` passed, we know that
         // these taint sets are mutually disjoint.
-        let inv_skol_map: FnvHashMap<&'tcx ty::Region, ty::BoundRegion> =
+        let inv_skol_map: FxHashMap<&'tcx ty::Region, ty::BoundRegion> =
             skol_map
             .iter()
             .flat_map(|(&skol_br, &skol)| {
@@ -837,7 +836,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                           snapshot: &CombinedSnapshot)
     {
         debug!("pop_skolemized({:?})", skol_map);
-        let skol_regions: FnvHashSet<_> = skol_map.values().cloned().collect();
+        let skol_regions: FxHashSet<_> = skol_map.values().cloned().collect();
         self.region_vars.pop_skolemized(&skol_regions, &snapshot.region_vars_snapshot);
         if !skol_map.is_empty() {
             self.projection_cache.borrow_mut().rollback_skolemized(

src/librustc/infer/mod.rs

@@ -39,7 +39,7 @@ use std::fmt;
 use syntax::ast;
 use errors::DiagnosticBuilder;
 use syntax_pos::{self, Span, DUMMY_SP};
-use util::nodemap::{FnvHashMap, FnvHashSet, NodeMap};
+use util::nodemap::{FxHashMap, FxHashSet, NodeMap};
 
 use self::combine::CombineFields;
 use self::higher_ranked::HrMatchResult;
@@ -134,7 +134,7 @@ pub struct InferCtxt<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 
     // the set of predicates on which errors have been reported, to
     // avoid reporting the same error twice.
-    pub reported_trait_errors: RefCell<FnvHashSet<traits::TraitErrorKey<'tcx>>>,
+    pub reported_trait_errors: RefCell<FxHashSet<traits::TraitErrorKey<'tcx>>>,
 
     // Sadly, the behavior of projection varies a bit depending on the
     // stage of compilation. The specifics are given in the
@@ -170,7 +170,7 @@ 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> = FnvHashMap<ty::BoundRegion, &'tcx ty::Region>;
+pub type SkolemizationMap<'tcx> = FxHashMap<ty::BoundRegion, &'tcx ty::Region>;
 
 /// Why did we require that the two types be related?
 ///
@@ -492,7 +492,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'gcx> {
             selection_cache: traits::SelectionCache::new(),
             evaluation_cache: traits::EvaluationCache::new(),
             projection_cache: RefCell::new(traits::ProjectionCache::new()),
-            reported_trait_errors: RefCell::new(FnvHashSet()),
+            reported_trait_errors: RefCell::new(FxHashSet()),
             projection_mode: Reveal::NotSpecializable,
             tainted_by_errors_flag: Cell::new(false),
             err_count_on_creation: self.sess.err_count(),
@@ -531,7 +531,7 @@ impl<'a, 'gcx, 'tcx> InferCtxtBuilder<'a, 'gcx, 'tcx> {
             parameter_environment: param_env,
             selection_cache: traits::SelectionCache::new(),
             evaluation_cache: traits::EvaluationCache::new(),
-            reported_trait_errors: RefCell::new(FnvHashSet()),
+            reported_trait_errors: RefCell::new(FxHashSet()),
             projection_mode: projection_mode,
             tainted_by_errors_flag: Cell::new(false),
             err_count_on_creation: tcx.sess.err_count(),
@@ -1530,7 +1530,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         span: Span,
         lbrct: LateBoundRegionConversionTime,
         value: &ty::Binder<T>)
-        -> (T, FnvHashMap<ty::BoundRegion, &'tcx ty::Region>)
+        -> (T, FxHashMap<ty::BoundRegion, &'tcx ty::Region>)
         where T : TypeFoldable<'tcx>
     {
         self.tcx.replace_late_bound_regions(

src/librustc/infer/region_inference/graphviz.rs

@@ -23,7 +23,7 @@ use middle::region::CodeExtent;
 use super::Constraint;
 use infer::SubregionOrigin;
 use infer::region_inference::RegionVarBindings;
-use util::nodemap::{FnvHashMap, FnvHashSet};
+use util::nodemap::{FxHashMap, FxHashSet};
 
 use std::borrow::Cow;
 use std::collections::hash_map::Entry::Vacant;
@@ -122,8 +122,8 @@ pub fn maybe_print_constraints_for<'a, 'gcx, 'tcx>(
 struct ConstraintGraph<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     tcx: TyCtxt<'a, 'gcx, 'tcx>,
     graph_name: String,
-    map: &'a FnvHashMap<Constraint<'tcx>, SubregionOrigin<'tcx>>,
-    node_ids: FnvHashMap<Node, usize>,
+    map: &'a FxHashMap<Constraint<'tcx>, SubregionOrigin<'tcx>>,
+    node_ids: FxHashMap<Node, usize>,
 }
 
 #[derive(Clone, Hash, PartialEq, Eq, Debug, Copy)]
@@ -145,7 +145,7 @@ impl<'a, 'gcx, 'tcx> ConstraintGraph<'a, 'gcx, 'tcx> {
            map: &'a ConstraintMap<'tcx>)
            -> ConstraintGraph<'a, 'gcx, 'tcx> {
         let mut i = 0;
-        let mut node_ids = FnvHashMap();
+        let mut node_ids = FxHashMap();
         {
             let mut add_node = |node| {
                 if let Vacant(e) = node_ids.entry(node) {
@@ -235,7 +235,7 @@ impl<'a, 'gcx, 'tcx> dot::GraphWalk<'a> for ConstraintGraph<'a, 'gcx, 'tcx> {
     type Node = Node;
     type Edge = Edge<'tcx>;
     fn nodes(&self) -> dot::Nodes<Node> {
-        let mut set = FnvHashSet();
+        let mut set = FxHashSet();
         for node in self.node_ids.keys() {
             set.insert(*node);
         }
@@ -261,7 +261,7 @@ impl<'a, 'gcx, 'tcx> dot::GraphWalk<'a> for ConstraintGraph<'a, 'gcx, 'tcx> {
     }
 }
 
-pub type ConstraintMap<'tcx> = FnvHashMap<Constraint<'tcx>, SubregionOrigin<'tcx>>;
+pub type ConstraintMap<'tcx> = FxHashMap<Constraint<'tcx>, SubregionOrigin<'tcx>>;
 
 fn dump_region_constraints_to<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
                                               map: &ConstraintMap<'tcx>,