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, 2 insertions, 2 deletions

diff --git a/tvix/eval/src/value/thunk.rs b/tvix/eval/src/value/thunk.rs
index 6d1fe1b8a7cc..2019e8ab3239 100644
--- a/tvix/eval/src/value/thunk.rs
+++ b/tvix/eval/src/value/thunk.rs
@@ -18,9 +18,9 @@
 //! object, but when forcing a thunk, the runtime *must* mutate the
 //! memoisable slot.
 
+use rustc_hash::FxHashSet;
 use std::{
     cell::{Ref, RefCell, RefMut},
-    collections::HashSet,
     fmt::Debug,
     rc::Rc,
 };
@@ -413,7 +413,7 @@ impl TotalDisplay for Thunk {
 /// The inner `HashSet` is not available on the outside, as it would be
 /// potentially unsafe to interact with the pointers in the set.
 #[derive(Default)]
-pub struct ThunkSet(HashSet<*const ThunkRepr>);
+pub struct ThunkSet(FxHashSet<*const ThunkRepr>);
 
 impl ThunkSet {
     /// Check whether the given thunk has already been seen. Will mark the thunk