Compare string search performance of phf::Map and FxHashMap

Author: petrochenkov

compiler/rustc_span/src/lib.rs

@@ -22,6 +22,7 @@
 #![feature(nll)]
 #![feature(min_specialization)]
 #![feature(option_expect_none)]
+#![feature(zzz)]
 
 #[macro_use]
 extern crate rustc_macros;

compiler/rustc_span/src/symbol.rs

@@ -1,3 +1,5 @@
+// ignore-tidy-filelength
+
 //! An "interner" is a data structure that associates values with usize tags and
 //! allows bidirectional lookup; i.e., given a value, one can easily find the
 //! type, and vice versa.
@@ -5056,7 +5058,7 @@ impl Symbol {
 
     /// Maps a string to its interned representation.
     pub fn intern(string: &str) -> Self {
-        if let Some(symbol) = STATIC_SYMBOLS_PHF.get(string) {
+        if let Some(symbol) = unsafe { STATIC_SYMBOLS.get(string) } {
             *symbol
         } else {
             with_interner(|interner| interner.intern(string))
@@ -5141,13 +5143,23 @@ pub struct Interner {
     strings: Vec<&'static str>,
 }
 
+use std::hash::BuildHasherDefault;
+use std::marker::PhantomData;
+
+#[allow(unused)]
+static mut STATIC_SYMBOLS: FxHashMap<&'static str, Symbol> =
+    FxHashMap::with_hasher(BuildHasherDefault(PhantomData));
+
 impl Interner {
     fn prefill(init: &[&'static str]) -> Self {
-        Interner {
-            strings: init.into(),
-            names: init.iter().copied().zip((0..).map(Symbol::new)).collect(),
-            ..Default::default()
+        let names: FxHashMap<_, _> = init.iter().copied().zip((0..).map(Symbol::new)).collect();
+        unsafe {
+            STATIC_SYMBOLS = names.clone();
+            // Some memory fence must go here,
+            // and all accesses to `Symbol::intern` must go after it.
         }
+
+        Interner { strings: init.into(), names, ..Default::default() }
     }
 
     #[inline]

library/core/src/hash/mod.rs

@@ -496,7 +496,9 @@ pub trait BuildHasher {
 /// [`HashSet`]: ../../std/collections/struct.HashSet.html
 /// [zero-sized]: https://doc.rust-lang.org/nomicon/exotic-sizes.html#zero-sized-types-zsts
 #[stable(since = "1.7.0", feature = "build_hasher")]
-pub struct BuildHasherDefault<H>(marker::PhantomData<H>);
+pub struct BuildHasherDefault<H>(
+    #[stable(since = "1.7.0", feature = "build_hasher")] pub marker::PhantomData<H>,
+);
 
 #[stable(since = "1.9.0", feature = "core_impl_debug")]
 impl<H> fmt::Debug for BuildHasherDefault<H> {

library/std/src/collections/hash/map.rs

@@ -263,7 +263,8 @@ impl<K, V, S> HashMap<K, V, S> {
     /// ```
     #[inline]
     #[stable(feature = "hashmap_build_hasher", since = "1.7.0")]
-    pub fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
+    #[rustc_const_unstable(feature = "zzz", issue = "123456")]
+    pub const fn with_hasher(hash_builder: S) -> HashMap<K, V, S> {
         HashMap { base: base::HashMap::with_hasher(hash_builder) }
     }