feat(minifier): support ForStatements for single use variable inlining

[sapphi-red]

Inline single use variables in for statements:

function wrapper1() { var x = foo; for (var i = x; i < 10; i++) console.log(i) }
function wrapper2() { var i, x = foo; for (i = x; i < 10; i++) console.log(i) }
// to
function wrapper1() { for (var i = foo; i < 10; i++) console.log(i) }
function wrapper2() { var i; for (i = foo; i < 10; i++) console.log(i) }

function wrapper() { var x = {}; for (var a in x) console.log(a) }
// to
function wrapper() { for (var a in {}) console.log(a) }

function wrapper() { var x = []; for (var a of x) console.log(a) }
// to
function wrapper() { for (var a of []) console.log(a) }

refs #13277

[sapphi-red]

• feat(minifier): support ForStatements for single use variable inlining #13755 👈 (View in Graphite)
• main

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[Copilot]

Pull Request Overview

This PR extends the single use variable inlining optimization to support for-in and for-of statements. The minifier can now inline variables that are used only once in the right-hand side expression of these loop constructs.

• Adds single use variable substitution for for-in and for-of statement right-hand side expressions
• Includes proper handling of variable declaration initializers in for-in statements (Annex B.3.5)
• Updates test coverage with new test cases for both for-in and for-of scenarios

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
crates/oxc_minifier/src/peephole/minimize_statements.rs	Implements single use variable substitution for for-in and for-of statements
crates/oxc_minifier/tests/peephole/inline_single_use_variable.rs	Adds test cases for the new optimization
tasks/track_memory_allocations/allocs_minifier.snap	Updates memory allocation benchmarks
tasks/minsize/minsize.snap	Updates minification size benchmarks

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[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #13755 will not alter performance

_{Comparing 09-14-feat_minifier_support_for-in_and_for-of_statements_for_single_use_variable_inlining (c364ad1) with main (c868796)¹}

Summary

✅ 37 untouched

Footnotes

1. No successful run was found on main (c364ad1) during the generation of this report, so c868796 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[Boshen]

Merge activity

• Sep 14, 12:54 PM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Sep 14, 12:54 PM UTC: Boshen added this pull request to the Graphite merge queue.
• Sep 14, 1:01 PM UTC: Merged by the Graphite merge queue.