feat(tvix/eval): Forbid Hash{Map,Set}, use Fx instead r/8453

Per https://nnethercote.github.io/perf-book/hashing.html, we have
basically no reason to use the default hasher over a faster,
non-DoS-resistant hasher. This gives a nice perf boost basically for
free:

hello outpath           time:   [704.76 ms 714.91 ms 725.63 ms]
                        change: [-7.2391% -6.1018% -4.9189%] (p = 0.00 < 0.05)
                        Performance has improved.

Change-Id: If5587f444ed3af69f8af4eead6af3ea303b4ae68
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12046
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
Reviewed-by: Ilan Joselevich <personal@ilanjoselevich.com>
Autosubmit: aspen <root@gws.fyi>

3 files changed, 11 insertions, 12 deletions

diff --git a/tvix/eval/src/compiler/bindings.rs b/tvix/eval/src/compiler/bindings.rs
index 60203ba5d94b..f5c6376eb1b3 100644
--- a/tvix/eval/src/compiler/bindings.rs
+++ b/tvix/eval/src/compiler/bindings.rs
@@ -560,7 +560,7 @@ impl Compiler<'_, '_> {
 
     /// Emit definitions for all variables in the top-level global env passed to the evaluation (eg
     /// local variables in the REPL)
-    pub(super) fn compile_env(&mut self, env: &HashMap<SmolStr, Value>) {
+    pub(super) fn compile_env(&mut self, env: &FxHashMap<SmolStr, Value>) {
         for (name, value) in env {
             self.scope_mut().declare_constant(name.to_string());
             self.emit_constant(value.clone(), &EntireFile);
diff --git a/tvix/eval/src/compiler/mod.rs b/tvix/eval/src/compiler/mod.rs
index 3a25052aabb2..4878db1f1a84 100644
--- a/tvix/eval/src/compiler/mod.rs
+++ b/tvix/eval/src/compiler/mod.rs
@@ -20,8 +20,9 @@ mod scope;
 
 use codemap::Span;
 use rnix::ast::{self, AstToken};
+use rustc_hash::FxHashMap;
 use smol_str::SmolStr;
-use std::collections::{BTreeMap, HashMap};
+use std::collections::BTreeMap;
 use std::path::{Path, PathBuf};
 use std::rc::{Rc, Weak};
 
@@ -117,7 +118,7 @@ impl TrackedFormal {
 
 /// The map of globally available functions and other values that
 /// should implicitly be resolvable in the global scope.
-pub type GlobalsMap = HashMap<&'static str, Value>;
+pub type GlobalsMap = FxHashMap<&'static str, Value>;
 
 /// Set of builtins that (if they exist) should be made available in
 /// the global scope, meaning that they can be accessed not just
@@ -187,7 +188,7 @@ impl<'source, 'observer> Compiler<'source, 'observer> {
     pub(crate) fn new(
         location: Option<PathBuf>,
         globals: Rc<GlobalsMap>,
-        env: Option<&HashMap<SmolStr, Value>>,
+        env: Option<&FxHashMap<SmolStr, Value>>,
         source: &'source SourceCode,
         file: &'source codemap::File,
         observer: &'observer mut dyn CompilerObserver,
@@ -1588,7 +1589,7 @@ pub fn prepare_globals(
     Rc::new_cyclic(Box::new(move |weak: &Weak<GlobalsMap>| {
         // First step is to construct the builtins themselves as
         // `NixAttrs`.
-        let mut builtins: GlobalsMap = HashMap::from_iter(builtins);
+        let mut builtins: GlobalsMap = FxHashMap::from_iter(builtins);
 
         // At this point, optionally insert `import` if enabled. To
         // "tie the knot" of `import` needing the full set of globals
@@ -1601,7 +1602,7 @@ pub fn prepare_globals(
 
         // Next, the actual map of globals which the compiler will use
         // to resolve identifiers is constructed.
-        let mut globals: GlobalsMap = HashMap::new();
+        let mut globals: GlobalsMap = FxHashMap::default();
 
         // builtins contain themselves (`builtins.builtins`), which we
         // can resolve by manually constructing a suspended thunk that
@@ -1654,7 +1655,7 @@ pub fn compile(
     expr: &ast::Expr,
     location: Option<PathBuf>,
     globals: Rc<GlobalsMap>,
-    env: Option<&HashMap<SmolStr, Value>>,
+    env: Option<&FxHashMap<SmolStr, Value>>,
     source: &SourceCode,
     file: &codemap::File,
     observer: &mut dyn CompilerObserver,
diff --git a/tvix/eval/src/compiler/scope.rs b/tvix/eval/src/compiler/scope.rs
index 7b0a66004a7f..1087e0153e42 100644
--- a/tvix/eval/src/compiler/scope.rs
+++ b/tvix/eval/src/compiler/scope.rs
@@ -10,10 +10,8 @@
 //! stack indices. To do this, the compiler simulates where locals
 //! will be at runtime using the data structures implemented here.
 
-use std::{
-    collections::{hash_map, HashMap},
-    ops::Index,
-};
+use rustc_hash::FxHashMap;
+use std::{collections::hash_map, ops::Index};
 
 use smol_str::SmolStr;
 
@@ -168,7 +166,7 @@ pub struct Scope {
     pub upvalues: Vec<Upvalue>,
 
     /// Secondary by-name index over locals.
-    by_name: HashMap<String, ByName>,
+    by_name: FxHashMap<String, ByName>,
 
     /// How many scopes "deep" are these locals?
     scope_depth: usize,