avoid clones when making an Artifact from a Compilation

[Ekleog-NEAR]

Performance characteristics of uncached compilation (not including
preparation) for the wasm blob from near/nearcore-private-1#2:

       | Non-rayon |   Rayon
-------+-----------+-----------
Before | 28.5-29ms | 15-15.5ms
After  | 25-25.5ms |    12ms

[nagisa]

Seems good to me. Making the fields pub seems okay too, since the Compilation struct doesn't appear to have any invariants per-se.

[Ekleog-NEAR]

I’m under the same impression, especially as Compilation seems used at exactly one place right now, ie. where I removed the spurious clones. Landing, then :)

[matklad]

WDYT about making a release and pulling this work into nearcore, such that we don't accumulate unbatletested stuff in this repo?

[Ekleog-NEAR]

I’d be ok with it, but maybe in 1-2 weeks after I complete the work on these things so we don’t spend too much energy making releases?

[matklad]

SGTM, though in the limit we hsould make release process rather lightweright ideally.

[akhi3030]

@Ekleog-NEAR : I am curious how you determined that this change would result in a performance improvement. Maybe we can discuss it a bit in our next 1-1.

[Ekleog-NEAR]

Might as well write it down here so other people can read it too :)

The steps I followed to identify the opportunity for this PR are:

1. Have a GCP VM with the setup we recommend validators have
2. Run the test from nearcore-private-1#2 (with a small diff to only test wasmer2) in --release inside perf (I needed to add debug = true to profile.release)
3. Load it inside profiler.firefox.com
4. Look at the trace, identify what looked like bottlenecks (IIRC quite a lot of time was being spent in iterators that deep down ended up cloning stuff)
5. Open the code, and see that we were indeed cloning lots of stuff that didn’t need to
6. Make the PR

Then, to measure the exact performance benefits:

1. On the same GCP VM,
2. With the following diff on top of nearcore:

diff --git a/runtime/near-vm-runner/src/cache.rs b/runtime/near-vm-runner/src/cache.rs
index f7bd1a49b..6d1f7df5e 100644
--- a/runtime/near-vm-runner/src/cache.rs
+++ b/runtime/near-vm-runner/src/cache.rs
@@ -259,9 +259,14 @@ pub mod wasmer2_cache {
         config: &VMConfig,
     ) -> Result<wasmer_engine_universal::UniversalExecutable, CompilationError> {
         let _span = tracing::debug_span!(target: "vm", "compile_module_wasmer2").entered();
+        let time = std::time::SystemTime::now();
         let prepared_code =
             prepare::prepare_contract(code, config).map_err(CompilationError::PrepareError)?;
-        vm.compile_uncached(&prepared_code)
+        eprintln!("Preparation: {:?}", time.elapsed());
+        let time = std::time::SystemTime::now();
+        let r = vm.compile_uncached(&prepared_code);
+        eprintln!("Uncached compilation: {:?}", time.elapsed());
+        r
     }

     pub(crate) fn compile_and_serialize_wasmer2(

3. Run a few times before and after the change
4. Run again a few times before and after the change, but with this diff in addition to exclude rayon:

diff --git a/runtime/near-vm-runner/Cargo.toml b/runtime/near-vm-runner/Cargo.toml
index 44e03bfb2..cd8e653e6 100644
--- a/runtime/near-vm-runner/Cargo.toml
+++ b/runtime/near-vm-runner/Cargo.toml
@@ -54,7 +54,7 @@ wasmer-runtime-core = { version = "0.18.2", package = "wasmer-runtime-core-near"
 #wasmer-types = { package = "wasmer-types-near", version = "=2.4.0", optional = true }
 #wasmer-vm = { package = "wasmer-vm-near", version = "=2.4.0", optional = true }
 wasmer-compiler = { package = "wasmer-compiler-near", path = "../../../wasmer/lib/compiler", optional = true }
-wasmer-compiler-singlepass = { package = "wasmer-compiler-singlepass-near", path = "../../../wasmer/lib/compiler-singlepass", optional = true }
+wasmer-compiler-singlepass = { package = "wasmer-compiler-singlepass-near", path = "../../../wasmer/lib/compiler-singlepass", optional = true, default-features = false, features = ["std"] }
 wasmer-engine = { package = "wasmer-engine-near", path = "../../../wasmer/lib/engine", optional = true }
 wasmer-engine-universal = { package = "wasmer-engine-universal-near", path = "../../../wasmer/lib/engine-universal", features = ["compiler"], optional = true }
 wasmer-types = { package = "wasmer-types-near", path = "../../../wasmer/lib/types", optional = true }