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feat(minifier): support ForStatements for single use variable inlining #13755

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Merged
merged 1 commit into from
Sep 14, 2025
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feat(minifier): support ForStatements for single use variable inlining #13755

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48 changes: 48 additions & 0 deletions crates/oxc_minifier/src/peephole/minimize_statements.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -824,6 +824,33 @@ impl<'a> PeepholeOptimizations {

ctx: &mut Ctx<'a, '_>,
) {
if let Some(init) = &mut for_stmt.init {
match init {
ForStatementInit::VariableDeclaration(var_decl) => {
if let Some(first_decl) = var_decl.declarations.first_mut()
&& let Some(first_decl_init) = first_decl.init.as_mut()
{
let changed = Self::substitute_single_use_symbol_in_statement(
first_decl_init,
result,
ctx,
);
if changed {
ctx.state.changed = true;
}
}
}
match_expression!(ForStatementInit) => {
let init = init.to_expression_mut();
let changed =
Self::substitute_single_use_symbol_in_statement(init, result, ctx);
if changed {
ctx.state.changed = true;
}
}
}
}

if let Some(ForStatementInit::VariableDeclaration(var_decl)) = &mut for_stmt.init {
let old_len = var_decl.declarations.len();
var_decl.declarations.retain(|decl| {
Expand Down Expand Up @@ -890,6 +917,21 @@ impl<'a> PeepholeOptimizations {

ctx: &mut Ctx<'a, '_>,
) {
// Annex B.3.5 allows initializers in non-strict mode
// <https://tc39.es/ecma262/multipage/additional-ecmascript-features-for-web-browsers.html#sec-initializers-in-forin-statement-heads>
// That is evaluated before the right hand side is evaluated. So, in that case, skip the single use substitution.
if !matches!(&for_in_stmt.left, ForStatementLeft::VariableDeclaration(var_decl) if var_decl.has_init())
{
let changed = Self::substitute_single_use_symbol_in_statement(
&mut for_in_stmt.right,
result,
ctx,
);
if changed {
ctx.state.changed = true;
}
}

if ctx.options().sequences {
match result.last_mut() {
// "a; for (var b in c) d" => "for (var b in a, c) d"
Expand Down Expand Up @@ -963,6 +1005,12 @@ impl<'a> PeepholeOptimizations {
result: &mut Vec<'a, Statement<'a>>,
ctx: &mut Ctx<'a, '_>,
) {
let changed =
Self::substitute_single_use_symbol_in_statement(&mut for_of_stmt.right, result, ctx);
if changed {
ctx.state.changed = true;
}

// "var a; for (a of b) c" => "for (var a of b) c"
if let Some(Statement::VariableDeclaration(prev_var_decl)) = result.last_mut() {
if let ForStatementLeft::AssignmentTargetIdentifier(id) = &for_of_stmt.left {
Expand Down
21 changes: 21 additions & 0 deletions crates/oxc_minifier/tests/peephole/inline_single_use_variable.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -154,6 +154,27 @@ fn test_inline_single_use_variable() {
"function wrapper() { let x = function () { console.log() }; foo(x) }",
"function wrapper() { foo(function() { console.log() }) }",
);

test(
"function wrapper() { var x = foo; for (var i = x; i < 10; i++) console.log(i) }",
"function wrapper() { for (var i = foo; i < 10; i++) console.log(i) }",
);
test(
"function wrapper() { var i, x = foo; for (i = x; i < 10; i++) console.log(i) }",
"function wrapper() { var i; for (i = foo; i < 10; i++) console.log(i) }",
);
test(
"function wrapper() { var x = {}; for (var a in x) console.log(a) }",
"function wrapper() { for (var a in {}) console.log(a) }",
);
test(
"function wrapper() { var x = {}; for (var a = 0 in x) console.log(a) }",
"function wrapper() { var x = {}; for (var a = 0 in x) console.log(a) }",
);
test(
"function wrapper() { var x = []; for (var a of x) console.log(a) }",
"function wrapper() { for (var a of []) console.log(a) }",
);
}

#[test]
Expand Down
8 changes: 4 additions & 4 deletions tasks/minsize/minsize.snap
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Original file line number Diff line number Diff line change
Expand Up @@ -7,19 +7,19 @@ Original | minified | minified | gzip | gzip | Iterations | Fi

287.63 kB | 89.28 kB | 90.07 kB | 30.94 kB | 31.95 kB | 2 | jquery.js

342.15 kB | 117.01 kB | 118.14 kB | 43.19 kB | 44.37 kB | 2 | vue.js
342.15 kB | 117 kB | 118.14 kB | 43.19 kB | 44.37 kB | 2 | vue.js

544.10 kB | 71.18 kB | 72.48 kB | 25.85 kB | 26.20 kB | 2 | lodash.js

555.77 kB | 270.78 kB | 270.13 kB | 88.19 kB | 90.80 kB | 2 | d3.js

1.01 MB | 439.58 kB | 458.89 kB | 122.15 kB | 126.71 kB | 2 | bundle.min.js
1.01 MB | 439.56 kB | 458.89 kB | 122.14 kB | 126.71 kB | 2 | bundle.min.js

1.25 MB | 645.63 kB | 646.76 kB | 159.54 kB | 163.73 kB | 2 | three.js

2.14 MB | 713.54 kB | 724.14 kB | 161.00 kB | 181.07 kB | 2 | victory.js
2.14 MB | 713.53 kB | 724.14 kB | 160.99 kB | 181.07 kB | 2 | victory.js

3.20 MB | 1.00 MB | 1.01 MB | 323.12 kB | 331.56 kB | 3 | echarts.js
3.20 MB | 1.00 MB | 1.01 MB | 323.10 kB | 331.56 kB | 3 | echarts.js

6.69 MB | 2.22 MB | 2.31 MB | 459.28 kB | 488.28 kB | 4 | antd.js

Expand Down
4 changes: 2 additions & 2 deletions tasks/track_memory_allocations/allocs_minifier.snap
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Original file line number Diff line number Diff line change
@@ -1,12 +1,12 @@
File | File size || Sys allocs | Sys reallocs || Arena allocs | Arena reallocs | Arena bytes
-------------------------------------------------------------------------------------------------------------------------------------------
checker.ts | 2.92 MB || 84073 | 14190 || 153691 | 29463 | 5.625 MB
checker.ts | 2.92 MB || 84058 | 14190 || 153533 | 29395 | 5.615 MB

cal.com.tsx | 1.06 MB || 40525 | 3033 || 37074 | 4733 | 1.654 MB

RadixUIAdoptionSection.jsx | 2.52 kB || 82 | 8 || 30 | 6 | 992 B

pdf.mjs | 567.30 kB || 19577 | 2900 || 47405 | 7784 | 1.625 MB
pdf.mjs | 567.30 kB || 19572 | 2900 || 47384 | 7770 | 1.623 MB

antd.js | 6.69 MB || 99854 | 13518 || 331725 | 70117 | 17.407 MB

Expand Down
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