Minor optimizations to the codegen of TaskFnInputFunction

[bgw]

What?

I noticed a number of small optimizations that could be applied to these hot and heavily-monomorphized functions:

• Using with_context() instead of .context(), to avoid evaluating the error message in the common case that it's unused. I also tried concat!() since this can be a static string, but the resulting binary is slightly larger, and we don't need to optimize for the unlikely error case.
• Extracted the parts of the monomorphized functions that didn't require the type parameters into separate non-generic functions. While the goal here is mostly to reduce binary size and compilation time, this optimization on it's own seems to help with the runtime benchmarks too (though I didn't test it rigorously in isolation).

Here's a section from Rust for Rustaceans explaining this "non-generic function" trick:

Binary Size?

Slightly negative, at least for stripped debug builds:

time pnpm pack-next

-rw-r--r-- 1 bgw bgw 167895040 Jun  4 17:20 next-swc.after.tar
-rw-r--r-- 1 bgw bgw 168622080 Jun  4 15:37 next-swc.before.tar

Runtime Performance?

Using https://github.com/bgw/benchmark-scripts/

Microbenchmark (turbo_tasks_memory_stress/fibonacci/200)

$ TURBOPACK_BENCH_STRESS=yes cargo bench -p turbo-tasks-memory -- fibonacci/200
   Compiling turbo-tasks v0.1.0 (/home/bgw/turbo/crates/turbo-tasks)
   Compiling turbo-tasks-memory v0.1.0 (/home/bgw/turbo/crates/turbo-tasks-memory)
   Compiling turbo-tasks-testing v0.1.0 (/home/bgw/turbo/crates/turbo-tasks-testing)
    Finished `bench` profile [optimized] target(s) in 10.79s
     Running benches/mod.rs (target/release/deps/mod-8c0f970371f8713d)
turbo_tasks_memory_stress/fibonacci/200
                        time:   [64.420 ms 64.683 ms 64.941 ms]
                        thrpt:  [309.53 Kelem/s 310.76 Kelem/s 312.03 Kelem/s]
                 change:
                        time:   [-2.2828% -1.7587% -1.2206%] (p = 0.00 < 0.05)
                        thrpt:  [+1.2357% +1.7902% +2.3361%]
                        Performance has improved.
Found 1 outliers among 20 measurements (5.00%)
  1 (5.00%) low mild

"Realistic" Benchmark (bench_startup/Turbopack CSR/1000 modules)

The difference is small. I patched the benchmark to increase the number of iterations so I could get something statistically significant.

diff --git a/crates/turbopack-bench/src/lib.rs b/crates/turbopack-bench/src/lib.rs
index 4e3df12db0..d950d76071 100644
--- a/crates/turbopack-bench/src/lib.rs
+++ b/crates/turbopack-bench/src/lib.rs
@@ -35,8 +35,8 @@ pub mod util;

 pub fn bench_startup(c: &mut Criterion, bundlers: &[Box<dyn Bundler>]) {
     let mut g = c.benchmark_group("bench_startup");
-    g.sample_size(10);
-    g.measurement_time(Duration::from_secs(60));
+    g.sample_size(100);
+    g.measurement_time(Duration::from_secs(600));

     bench_startup_internal(g, false, bundlers);
 }

cargo bench -p turbopack-cli -- bench_startup

    Finished `bench` profile [optimized] target(s) in 1.30s
     Running benches/mod.rs (target/release/deps/mod-2681e324dfd90da1)
bench_startup/Turbopack CSR/1000 modules
                        time:   [2.2684 s 2.2717 s 2.2750 s]
                        change: [-1.9365% -1.7387% -1.5602%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 3 outliers among 100 measurements (3.00%)
  1 (1.00%) low mild
  2 (2.00%) high mild

Build Speed?

Not enough of a difference to measure.

rm -rf target/ && time cargo build -p turbopack-cli

Before:

real    10m42.174s

After:

real    10m40.735s

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[bgw]

• Minor optimizations to the codegen of TaskFnInputFunction #8304 👈
• main

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[github-actions]

🟢 Turbopack Benchmark CI successful 🟢

Thanks

[github-actions]

✅ This change can build next-swc

[github-actions]

⚠️ CI failed ⚠️

The following steps have failed in CI:

• Turbopack Rust tests (mac/win, non-blocking)

See workflow summary for details