perf(minifier/minimize_statements): reduce allocations of Vec

[Dunqing]

Use ctx.ast.vec_from_iter to allocate a Vec for the result of drain and use take_in to take a Vec rather than use vec_from_iter + drain to avoid intermediate allocation.

[Dunqing]

• perf(minifier/minimize_statements): reduce allocations of Vec #10435 : 2 dependent PRs (#9881 , #10436 ) 👈 (View in Graphite)
• perf(transformer/object_rest_spread): use ArenaVec to store values that will be used in constructing AST #10434
• perf(transformer/class-properties): return early if no private fields are found #10418
• main

---

How to use the Graphite Merge Queue

Add either label to this PR to merge it via the merge queue:

• 0-merge - adds this PR to the back of the merge queue
• hotfix - for urgent hot fixes, skip the queue and merge this PR next

You must have a Graphite account in order to use the merge queue. Sign up using this link.

An organization admin has enabled the Graphite Merge Queue in this repository.

Please do not merge from GitHub as this will restart CI on PRs being processed by the merge queue.

This stack of pull requests is managed by Graphite. Learn more about stacking.

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #10435 will not alter performance

_{Comparing 04-16-perf_transformer_minimize_statements_reduce_allocations_of_vec (59e35c3) with main (ebe3496)}

Summary

✅ 36 untouched benchmarks

[overlookmotel]

Merge activity

• Apr 16, 8:41 AM EDT: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Apr 16, 9:28 AM EDT: overlookmotel added this pull request to the Graphite merge queue.

[overlookmotel]

Actually I think this might be even better:

Before:

let drained_stmts = stmts.drain(i + 1..);
let mut body = if let Some(alternate) = if_stmt.alternate.take() {
    ctx.ast.vec_from_iter(iter::once(alternate).chain(drained_stmts))
} else {
    ctx.ast.vec_from_iter(drained_stmts)
};

After:

let mut body = if let Some(alternate) = if_stmt.alternate.take() {
    let drained_stmts = stmts.drain(i + 1..);
    ctx.ast.vec_from_iter(iter::once(alternate).chain(drained_stmts))
} else {
    stmts.split_off(i + 1)
};

split_off avoids using vec_from_iter. It knows the exact required capacity of the new Vec.

---

Similar to my comment on preceding PR #10434 (comment), later on we can make our split_off implementation more efficient, not copying any data or performing any allocations.

Then this simpler version would be equally efficient (or possibly more, as if stmts has spare capacity, it avoids an allocation):

let mut body = stmts.split_off(i + 1);
if let Some(alternate) = if_stmt.alternate.take() {
    body.insert(0, alternate);
}