Try using AHash as the default hasher (again)

This still uses std::collections::HashMap since there were a lot of
issues with AHashMap.

This also enables the `specialize` feature in hopes of getting better
performance.

Author: jyn514

Cargo.lock

@@ -22,6 +22,16 @@ dependencies = [
  "rustc-std-workspace-core",
 ]
 
+[[package]]
+name = "ahash"
+version = "0.5.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4eb6ec8807cd25b59e6b8100815afc73f54e294f1a425a2e555971969889a8f8"
+dependencies = [
+ "getrandom 0.2.0",
+ "lazy_static",
+]
+
 [[package]]
 name = "aho-corasick"
 version = "0.7.13"
@@ -3572,6 +3582,7 @@ dependencies = [
 name = "rustc_data_structures"
 version = "0.0.0"
 dependencies = [
+ "ahash",
  "arrayvec",
  "bitflags",
  "cfg-if 0.1.10",
@@ -3582,7 +3593,6 @@ dependencies = [
  "libc",
  "measureme",
  "parking_lot 0.11.0",
- "rustc-hash",
  "rustc-rayon",
  "rustc-rayon-core",
  "rustc_graphviz",

compiler/rustc_data_structures/Cargo.toml

@@ -21,7 +21,8 @@ crossbeam-utils = { version = "0.7", features = ["nightly"] }
 stable_deref_trait = "1.0.0"
 rayon = { version = "0.3.0", package = "rustc-rayon" }
 rayon-core = { version = "0.3.0", package = "rustc-rayon-core" }
-rustc-hash = "1.1.0"
+#rustc-hash = "1.1.0"
+ahash = { version = "0.5.6", features = ["specialize"] }
 smallvec = { version = "1.0", features = ["union", "may_dangle"] }
 rustc_index = { path = "../rustc_index", package = "rustc_index" }
 bitflags = "1.2.1"

compiler/rustc_data_structures/src/fx.rs

@@ -1,6 +1,12 @@
+pub use ahash::AHasher as FxHasher;
+use ahash::RandomState;
+use std::collections::{HashMap, HashSet};
 use std::hash::BuildHasherDefault;
 
-pub use rustc_hash::{FxHashMap, FxHashSet, FxHasher};
+//pub use rustc_hash::{FxHashMap, FxHashSet, FxHasher};
+
+pub type FxHashMap<K, V> = HashMap<K, V, RandomState>;
+pub type FxHashSet<T> = HashSet<T, RandomState>;
 
 pub type FxIndexMap<K, V> = indexmap::IndexMap<K, V, BuildHasherDefault<FxHasher>>;
 pub type FxIndexSet<V> = indexmap::IndexSet<V, BuildHasherDefault<FxHasher>>;

compiler/rustc_data_structures/src/stable_map.rs

@@ -1,4 +1,4 @@
-pub use rustc_hash::FxHashMap;
+pub use crate::fx::FxHashMap;
 use std::borrow::Borrow;
 use std::collections::hash_map::Entry;
 use std::fmt;

compiler/rustc_data_structures/src/stable_set.rs

@@ -1,4 +1,4 @@
-pub use rustc_hash::FxHashSet;
+pub use crate::fx::FxHashSet;
 use std::borrow::Borrow;
 use std::fmt;
 use std::hash::Hash;

src/tools/clippy/clippy_lints/src/utils/mod.rs

@@ -34,7 +34,7 @@ use std::mem;
 use if_chain::if_chain;
 use rustc_ast::ast::{self, Attribute, LitKind};
 use rustc_attr as attr;
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::FxHasher;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
@@ -1500,8 +1500,9 @@ where
 
     let mut match_expr_list: Vec<(&T, &T)> = Vec::new();
 
-    let mut map: FxHashMap<_, Vec<&_>> =
-        FxHashMap::with_capacity_and_hasher(exprs.len(), BuildHasherDefault::default());
+    use std::collections::HashMap;
+    let mut map: HashMap<_, Vec<&_>, BuildHasherDefault<FxHasher>> =
+        HashMap::with_capacity_and_hasher(exprs.len(), BuildHasherDefault::default());
 
     for expr in exprs {
         match map.entry(hash(expr)) {