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>

1 files changed, 3 insertions, 2 deletions

diff --git a/tvix/eval/src/vm/mod.rs b/tvix/eval/src/vm/mod.rs
index 65117b79a0bc..a6d0941e8d7a 100644
--- a/tvix/eval/src/vm/mod.rs
+++ b/tvix/eval/src/vm/mod.rs
@@ -14,8 +14,9 @@ mod macros;
 
 use bstr::{BString, ByteSlice, ByteVec};
 use codemap::Span;
+use rustc_hash::FxHashMap;
 use serde_json::json;
-use std::{cmp::Ordering, collections::HashMap, ops::DerefMut, path::PathBuf, rc::Rc};
+use std::{cmp::Ordering, ops::DerefMut, path::PathBuf, rc::Rc};
 
 use crate::{
     arithmetic_op,
@@ -211,7 +212,7 @@ impl Frame {
 }
 
 #[derive(Default)]
-struct ImportCache(HashMap<PathBuf, Value>);
+struct ImportCache(FxHashMap<PathBuf, Value>);
 
 /// The `ImportCache` holds the `Value` resulting from `import`ing a certain
 /// file, so that the same file doesn't need to be re-evaluated multiple times.