Auto merge of #45282 - stjepang:experiment-ordermap, r=<try>

[Experiment] Replace HashMap with OrderMap

Do not merge.

This is just a simple experiment where I modified `FxHashMap` to use `OrderMap` instead of `HashMap`, as explained in #45273. Don't expect the code to look good. :)

cc @Mark-Simulacrum - Can we please run performance tests to see how this PR impacts compile times?
cc @bluss @kennytm

@eddyb said on IRC that we shouldn't blindly swap the implementation just yet - let's investigate a bit further. If changing the hash map implementation affects performance a lot, then we can probably gain even more by using a different data structure.

Author: bors

src/Cargo.lock

@@ -23,6 +23,7 @@ rustc_errors = { path = "../librustc_errors" }
 serialize = { path = "../libserialize" }
 syntax = { path = "../libsyntax" }
 syntax_pos = { path = "../libsyntax_pos" }
+ordermap = "0.3.0"
 
 # Note that these dependencies are a lie, they're just here to get linkage to
 # work.

src/librustc/Cargo.toml

@@ -41,7 +41,7 @@ impl DepGraphQuery {
     }
 
     pub fn contains_node(&self, node: &DepNode) -> bool {
-        self.indices.contains_key(&node)
+        self.indices.contains_key(node)
     }
 
     pub fn nodes(&self) -> Vec<&DepNode> {
@@ -83,7 +83,7 @@ impl DepGraphQuery {
 
     /// Just the outgoing edges from `node`.
     pub fn immediate_successors(&self, node: &DepNode) -> Vec<&DepNode> {
-        if let Some(&index) = self.indices.get(&node) {
+        if let Some(&index) = self.indices.get(node) {
             self.graph.successor_nodes(index)
                       .map(|s| self.graph.node_data(s))
                       .collect()

src/librustc/dep_graph/query.rs

@@ -21,7 +21,7 @@ use session::Session;
 use std::cmp::Ord;
 use std::hash as std_hash;
 use std::cell::RefCell;
-use std::collections::HashMap;
+use ordermap::OrderMap;
 
 use syntax::ast;
 use syntax::attr;
@@ -426,7 +426,7 @@ pub fn hash_stable_trait_impls<'gcx, W, R>(
     hcx: &mut StableHashingContext<'gcx>,
     hasher: &mut StableHasher<W>,
     blanket_impls: &Vec<DefId>,
-    non_blanket_impls: &HashMap<fast_reject::SimplifiedType, Vec<DefId>, R>)
+    non_blanket_impls: &OrderMap<fast_reject::SimplifiedType, Vec<DefId>, R>)
     where W: StableHasherResult,
           R: std_hash::BuildHasher,
 {

src/librustc/ich/hcx.rs

@@ -47,7 +47,7 @@ use ty::subst::Substs;
 use util::nodemap::FxHashMap;
 use hir::def_id::DefId;
 
-use std::collections::hash_map::Entry;
+use ordermap::Entry;
 
 use super::InferCtxt;
 use super::unify_key::ToType;

src/librustc/infer/freshen.rs

@@ -28,7 +28,7 @@ use infer::region_inference::RegionVarBindings;
 use util::nodemap::{FxHashMap, FxHashSet};
 
 use std::borrow::Cow;
-use std::collections::hash_map::Entry::Vacant;
+use ordermap::Entry::Vacant;
 use std::env;
 use std::fs::File;
 use std::io;

src/librustc/infer/region_inference/graphviz.rs

@@ -62,6 +62,7 @@
 
 #![recursion_limit="256"]
 
+extern crate ordermap;
 extern crate arena;
 #[macro_use] extern crate bitflags;
 extern crate core;

src/librustc/lib.rs

@@ -1263,7 +1263,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
         let trait_ref = &cache_fresh_trait_pred.0.trait_ref;
         if self.can_use_global_caches(param_env) {
             let cache = tcx.selection_cache.hashmap.borrow();
-            if let Some(cached) = cache.get(&trait_ref) {
+            if let Some(cached) = cache.get(trait_ref) {
                 return Some(cached.get(tcx));
             }
         }

src/librustc/traits/select.rs

@@ -53,15 +53,16 @@ use rustc_data_structures::accumulate_vec::AccumulateVec;
 use rustc_data_structures::stable_hasher::{HashStable, hash_stable_hashmap,
                                            StableHasher, StableHasherResult,
                                            StableVec};
+use rustc_data_structures;
 use arena::{TypedArena, DroplessArena};
 use rustc_const_math::{ConstInt, ConstUsize};
 use rustc_data_structures::indexed_vec::IndexVec;
 use std::any::Any;
 use std::borrow::Borrow;
 use std::cell::{Cell, RefCell};
 use std::cmp::Ordering;
-use std::collections::hash_map::{self, Entry};
-use std::hash::{Hash, Hasher};
+use ordermap::{self, Entry};
+use std::hash::{BuildHasherDefault, Hash, Hasher};
 use std::mem;
 use std::ops::Deref;
 use std::iter;
@@ -275,7 +276,7 @@ impl<'a, V> LocalTableInContext<'a, V> {
         self.data.get(&id.local_id)
     }
 
-    pub fn iter(&self) -> hash_map::Iter<hir::ItemLocalId, V> {
+    pub fn iter(&self) -> ordermap::Iter<hir::ItemLocalId, V> {
         self.data.iter()
     }
 }
@@ -299,7 +300,10 @@ impl<'a, V> LocalTableInContextMut<'a, V> {
         self.data.get_mut(&id.local_id)
     }
 
-    pub fn entry(&mut self, id: hir::HirId) -> Entry<hir::ItemLocalId, V> {
+    pub fn entry(
+        &mut self,
+        id: hir::HirId
+    ) -> Entry<hir::ItemLocalId, V, BuildHasherDefault<rustc_data_structures::fx::FxHasher>> {
         validate_hir_id_for_typeck_tables(self.local_id_root, id, true);
         self.data.entry(id.local_id)
     }

src/librustc/ty/context.rs

@@ -11,3 +11,4 @@ crate-type = ["dylib"]
 [dependencies]
 log = "0.3"
 serialize = { path = "../libserialize" }
+ordermap = "0.3.0"