feat(tvix/eval): nonrecursive nix_cmp_ordering(), fixes b/339 r/7167

This commit rewrites Value::nix_cmp_ordering() into an equivalent
nonrecursive form.  Except for calls to Thunk::force(), the new form
no longer uses generators, and is async only because of the fact
that it calls Thunk::force().

I originally believed that this commit would make evaluation faster.
In fact it is slightly slower.  I believe this is due to the added
vec![] allocation.  I am investigating.

Prev-Nixpkgs-Benchmark: {"attrpath":"pkgsCross.aarch64-multiplatform.hello.outPath","peak-kbytes":"460048","system-seconds":"0.68","user-seconds":"5.73"}
This-Nixpkgs-Benchmark: {"attrpath":"pkgsCross.aarch64-multiplatform.hello.outPath","peak-kbytes":"460224","system-seconds":"0.67","user-seconds":"5.84"}
Change-Id: Ic627bc220d9c5aa3c5e68b9b8bf199837cd55af5
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10212
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
Autosubmit: Adam Joseph <adam@westernsemico.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/tvix/eval/src/vm/macros.rs b/tvix/eval/src/vm/macros.rs
index 8a536ee4664d..34e94bb5fa74 100644
--- a/tvix/eval/src/vm/macros.rs
+++ b/tvix/eval/src/vm/macros.rs
@@ -42,7 +42,8 @@ macro_rules! cmp_op {
         async fn compare(a: Value, b: Value, co: GenCo) -> Result<Value, ErrorKind> {
             let a = generators::request_force(&co, a).await;
             let b = generators::request_force(&co, b).await;
-            let ordering = a.nix_cmp_ordering(b, co).await?;
+            let span = generators::request_span(&co).await;
+            let ordering = a.nix_cmp_ordering(b, co, span).await?;
             Ok(Value::Bool(cmp_op!(@order $op ordering)))
         }