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perf(minifier): reduce string allocations folding addition#23846

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Jun 29, 2026
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perf(minifier): reduce string allocations folding addition#23846
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@overlookmotel

@overlookmotel overlookmotel commented Jun 26, 2026

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Small perf optimization to minifier.

In constant-folding pass for addition, we were joining 2 strings together as a String, then allocating that string into the arena.

Instead, use Str::from_strs_array_in to build the concatenated string directly in the arena, avoiding allocating a temporary String in the middle.

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@github-actions github-actions Bot added the A-minifier Area - Minifier label Jun 26, 2026
@overlookmotel overlookmotel marked this pull request as ready for review June 26, 2026 19:14
@overlookmotel overlookmotel requested a review from Dunqing as a code owner June 26, 2026 19:14
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codspeed-hq Bot commented Jun 26, 2026

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Merging this PR will not alter performance

✅ 52 untouched benchmarks
⏩ 19 skipped benchmarks1


Comparing om/06-25-perf_minifier_reduce_string_allocations_folding_addition (809b076) with main (eff3eff)

Open in CodSpeed

Footnotes

  1. 19 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports.

@Dunqing Dunqing added the 0-merge Merge with Graphite Merge Queue label Jun 29, 2026

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graphite-app Bot pushed a commit that referenced this pull request Jun 29, 2026
Small perf optimization to minifier.

In constant-folding pass for addition, we were joining 2 strings together as a `String`, then allocating that string into the arena.

Instead, use `Str::from_strs_array_in` to build the concatenated string directly in the arena, avoiding allocating a temporary `String` in the middle.
@graphite-app graphite-app Bot force-pushed the om/06-25-perf_minifier_reduce_string_allocations_folding_addition branch from 809b076 to 537e654 Compare June 29, 2026 01:57
Small perf optimization to minifier.

In constant-folding pass for addition, we were joining 2 strings together as a `String`, then allocating that string into the arena.

Instead, use `Str::from_strs_array_in` to build the concatenated string directly in the arena, avoiding allocating a temporary `String` in the middle.
@graphite-app graphite-app Bot force-pushed the om/06-25-perf_minifier_reduce_string_allocations_folding_addition branch from 537e654 to e1f89ab Compare June 29, 2026 01:59
@graphite-app graphite-app Bot merged commit e1f89ab into main Jun 29, 2026
29 checks passed
@graphite-app graphite-app Bot removed the 0-merge Merge with Graphite Merge Queue label Jun 29, 2026
@graphite-app graphite-app Bot deleted the om/06-25-perf_minifier_reduce_string_allocations_folding_addition branch June 29, 2026 02:03
linyiru added a commit to linyiru/oxc that referenced this pull request Jun 29, 2026
`substitute_template_literal` called `TemplateLiteral::to_js_string`, which builds a
transient `std::String` (system allocation), then copied it into the arena via
`Str::from_cow_in`. Build the folded string directly in the arena instead:

- a single-quasi template (`` `abc` ``) reuses the cooked arena string with no
  allocation at all;
- the general case builds into a pre-sized `ArenaStringBuilder`.

Behaviour is identical — same all-or-nothing fold (bails if any quasi/expression
isn't stringifiable). Same technique as oxc-project#20386 / oxc-project#23846.

`cargo allocs` (system allocations):
  minifier  antd.js           3041 -> 2340
  minifier  kitchen-sink.tsx  2585 -> 684
  minifier  checker.ts         162 -> 53
  minifier  pdf.mjs           2587 -> 2227
linyiru added a commit to linyiru/oxc that referenced this pull request Jun 29, 2026
`substitute_template_literal` called `TemplateLiteral::to_js_string`, which builds a
transient `std::String` (system allocation), then copied it into the arena via
`Str::from_cow_in`. Build the folded string directly in the arena instead:

- a single-quasi template (`` `abc` ``) reuses the cooked arena string with no
  allocation at all;
- the general case builds into a pre-sized `ArenaStringBuilder`.

Behaviour is identical — same all-or-nothing fold (bails if any quasi/expression
isn't stringifiable). Same technique as oxc-project#20386 / oxc-project#23846.

`cargo allocs` (system allocations):
  minifier  antd.js           3041 -> 2340
  minifier  kitchen-sink.tsx  2585 -> 684
  minifier  checker.ts         162 -> 53
  minifier  pdf.mjs           2587 -> 2227
linyiru added a commit to linyiru/oxc that referenced this pull request Jun 29, 2026
`substitute_template_literal` folded a constant template literal into a string literal
by calling `TemplateLiteral::to_js_string`, which builds a transient `std::String`
(system allocation), then copied it into the arena via `Str::from_cow_in`. So every
folded template paid a system allocation for a string that immediately ends up in the
arena anyway.

This builds the folded string directly in the arena instead:
- a single-quasi template with no interpolations (`` `abc` ``) reuses the cooked arena
  string directly — no allocation at all;
- the general case builds into a pre-sized `ArenaStringBuilder`.

Behaviour is identical: the same all-or-nothing fold, byte-identical output. Same
technique as oxc-project#20386 / oxc-project#23846, applied to a spot that still went through std::String.

`cargo allocs` (minifier system allocations):
  kitchen-sink.tsx  2576 -> 675   (-74%)
  antd.js           1040 -> 339   (-701)
  pdf.mjs           2569 -> 2209
  checker.ts         162 -> 53

Arena allocations rise slightly (the intended std::String -> arena trade-off).
camc314 added a commit that referenced this pull request Jun 29, 2026
### 💥 BREAKING CHANGES

- 94fbacb ast: [**BREAKING**] Only export `AstBuilder` and `NONE` in
`builder` module (#23876) (overlookmotel)
- 8de5122 ecmascript: [**BREAKING**] Switch to new `AstBuilder` (#23834)
(overlookmotel)
- dc0ef38 transformer: [**BREAKING**] Switch to new `AstBuilder`
(#23831) (overlookmotel)
- 88f4455 str: [**BREAKING**] `Str` and `Ident` methods take
`&GetAllocator` (#23781) (overlookmotel)
- 36009dd allocator: [**BREAKING**] `GetAllocator::allocator` take
`&self` (#23676) (overlookmotel)
- bd74f9d allocator: [**BREAKING**] Rename `AllocatorAccessor` trait to
`GetAllocator` (#23675) (overlookmotel)

### 🚀 Features

- 326fe25 transformer_plugins: Support `typeof` `define` keys (#23605)
(Alexander Lichter)
- f2091b3 ast: Unify old and new `AstBuilder`s (#23875) (overlookmotel)
- cd1fd12 codegen: Expose `Codegen::print_string` API (#23785) (camc314)
- 785461b ast: Add custom builder methods to AST types (#23651)
(overlookmotel)
- 05d1357 ast: Add AST creation methods to AST types (#23650)
(overlookmotel)
- 2580eda str: Add `Str::from_str_in` and `Ident::from_str_in` methods
(#23767) (overlookmotel)
- 6883fcf minifier: Fold write-once falsy var to false in boolean
context (#23540) (Dunqing)
- fcbf993 allocator: Add `Vec::from_value_in` method (#23718)
(overlookmotel)
- 989ddb7 allocator: Add `Vec::from_box_in` method (#23717)
(overlookmotel)
- 9d1aa7f allocator: Improve `PartialEq` for `Vec` (#23716)
(overlookmotel)

### 🐛 Bug Fixes

- da0e5bf minifier: Don't reorder a closed-over TDZ read when inlining a
var (#23771) (Dunqing)
- 0b3021f allocator: Remove `Vec::from_box_in` (#23873) (overlookmotel)
- 0ab64ec ast: Silence deprecation warnings within files defining
deprecated `AstBuilder` methods (#23889) (overlookmotel)
- 8c07cad all: Enable `disable_old_builder` Cargo feature for `oxc_ast`
crate in tests (#23888) (overlookmotel)
- 3800f01 ast: Legacy `AstBuilder` methods take `self` not `&self`
(#23891) (overlookmotel)
- 869ac20 semantic/cfg: Connect for update exit to loop test (#23791)
(camc314)
- d3e92d5 semantic/cfg: Connect while branches from condition exit
(#23790) (camc314)
- 025045d ast: `ExportNamedDeclaration` plain builder methods return
boxed nodes (#23783) (overlookmotel)
- 7537c58 ast: Fix name of `AstBuilder` method for
`Expression::V8IntrinsicExpression` (#23766) (overlookmotel)
- 3f574f5 traverse: Fix unsoundness in `Traverse` walk functions
(#23745) (overlookmotel)
- 585760f parser: String in AST reference arena (#23721) (overlookmotel)
- 7231d55 allocator: Fix unsound lifetime extension in `Box::new_in`
(#23685) (overlookmotel)

### ⚡ Performance

- d5c916a semantic: Flatten hoisting_variables to avoid per-scope map
allocation (#23927) (Lawrence Lin)
- e71609d minifier: Bail member-expr folding before the side-effect walk
(#23924) (Lawrence Lin)
- e1f89ab minifier: Reduce string allocations folding addition (#23846)
(overlookmotel)
- 9f6ee3b isolated-declarations: Pool scope maps to avoid per-scope
alloc/rehash (#23761) (Boshen)
- 0b07c4c semantic: Avoid heap alloc for catch-clause binding ids
(#23911) (Lawrence Lin)
- c5eef8b regular_expression: Skip capturing-group pre-parse when
pattern has no `(` (#23908) (Lawrence Lin)
- b4f5b4b isolated_declarations: Remove redundant clone of formal
parameter pattern (#23912) (Lawrence Lin)
- 53d083f isolated_declarations: Use `TakeIn` not `CloneIn` (#23847)
(overlookmotel)
- 3ea9304 react_compiler: Use faster API to arena allocate strings
(#23849) (overlookmotel)
- a6d8e45 parser: Avoid span lookup for arrow expression body (#23788)
(camc314)
- e1886a0 transformer, minifier: Use `static_ident!` macro to create
static `Ident`s (#23727) (overlookmotel)
- 5527bef transformer/object-rest-spread: Reduce iteration (#23720)
(overlookmotel)
- 680ffbc transformer: Allocate AST nodes in arena directly (#23711)
(overlookmotel)
- 1c63c66 parser: Allocate AST nodes in arena directly (#23712)
(overlookmotel)
- 3855f0c minifier: Allocate AST nodes in arena directly (#23710)
(overlookmotel)
- d025887 isolated_declarations: Allocate AST nodes in arena directly
(#23709) (overlookmotel)
- 10b96c6 parser: Remove string search from parsing JSX element name
(#23713) (overlookmotel)

### 📚 Documentation

- 3d61dea all: Correct capitalization in comments (#23887)
(overlookmotel)
- aa1ad74 ast: Add `#[deprecated]` to legacy `AstBuilder` methods
(#23877) (overlookmotel)
- a4676db ast: Correct doc comment for `NONE` (#23765) (overlookmotel)
- 419ec80 syntax: Fix typo in doc comment (#23674) (overlookmotel)

### 🛡️ Security

- 3cdd18f deps: Update npm packages (#23690) (renovate[bot])

Co-authored-by: Boshen <1430279+Boshen@users.noreply.github.com>
Co-authored-by: Cameron <cameron.clark@hey.com>
camc314 pushed a commit that referenced this pull request Jul 3, 2026
Small perf optimization to minifier.

In constant-folding pass for addition, we were joining 2 strings together as a `String`, then allocating that string into the arena.

Instead, use `Str::from_strs_array_in` to build the concatenated string directly in the arena, avoiding allocating a temporary `String` in the middle.
camc314 added a commit that referenced this pull request Jul 3, 2026
### 💥 BREAKING CHANGES

- 94fbacb ast: [**BREAKING**] Only export `AstBuilder` and `NONE` in
`builder` module (#23876) (overlookmotel)
- 8de5122 ecmascript: [**BREAKING**] Switch to new `AstBuilder` (#23834)
(overlookmotel)
- dc0ef38 transformer: [**BREAKING**] Switch to new `AstBuilder`
(#23831) (overlookmotel)
- 88f4455 str: [**BREAKING**] `Str` and `Ident` methods take
`&GetAllocator` (#23781) (overlookmotel)
- 36009dd allocator: [**BREAKING**] `GetAllocator::allocator` take
`&self` (#23676) (overlookmotel)
- bd74f9d allocator: [**BREAKING**] Rename `AllocatorAccessor` trait to
`GetAllocator` (#23675) (overlookmotel)

### 🚀 Features

- 326fe25 transformer_plugins: Support `typeof` `define` keys (#23605)
(Alexander Lichter)
- f2091b3 ast: Unify old and new `AstBuilder`s (#23875) (overlookmotel)
- cd1fd12 codegen: Expose `Codegen::print_string` API (#23785) (camc314)
- 785461b ast: Add custom builder methods to AST types (#23651)
(overlookmotel)
- 05d1357 ast: Add AST creation methods to AST types (#23650)
(overlookmotel)
- 2580eda str: Add `Str::from_str_in` and `Ident::from_str_in` methods
(#23767) (overlookmotel)
- 6883fcf minifier: Fold write-once falsy var to false in boolean
context (#23540) (Dunqing)
- fcbf993 allocator: Add `Vec::from_value_in` method (#23718)
(overlookmotel)
- 989ddb7 allocator: Add `Vec::from_box_in` method (#23717)
(overlookmotel)
- 9d1aa7f allocator: Improve `PartialEq` for `Vec` (#23716)
(overlookmotel)

### 🐛 Bug Fixes

- da0e5bf minifier: Don't reorder a closed-over TDZ read when inlining a
var (#23771) (Dunqing)
- 0b3021f allocator: Remove `Vec::from_box_in` (#23873) (overlookmotel)
- 0ab64ec ast: Silence deprecation warnings within files defining
deprecated `AstBuilder` methods (#23889) (overlookmotel)
- 8c07cad all: Enable `disable_old_builder` Cargo feature for `oxc_ast`
crate in tests (#23888) (overlookmotel)
- 3800f01 ast: Legacy `AstBuilder` methods take `self` not `&self`
(#23891) (overlookmotel)
- 869ac20 semantic/cfg: Connect for update exit to loop test (#23791)
(camc314)
- d3e92d5 semantic/cfg: Connect while branches from condition exit
(#23790) (camc314)
- 025045d ast: `ExportNamedDeclaration` plain builder methods return
boxed nodes (#23783) (overlookmotel)
- 7537c58 ast: Fix name of `AstBuilder` method for
`Expression::V8IntrinsicExpression` (#23766) (overlookmotel)
- 3f574f5 traverse: Fix unsoundness in `Traverse` walk functions
(#23745) (overlookmotel)
- 585760f parser: String in AST reference arena (#23721) (overlookmotel)
- 7231d55 allocator: Fix unsound lifetime extension in `Box::new_in`
(#23685) (overlookmotel)

### ⚡ Performance

- d5c916a semantic: Flatten hoisting_variables to avoid per-scope map
allocation (#23927) (Lawrence Lin)
- e71609d minifier: Bail member-expr folding before the side-effect walk
(#23924) (Lawrence Lin)
- e1f89ab minifier: Reduce string allocations folding addition (#23846)
(overlookmotel)
- 9f6ee3b isolated-declarations: Pool scope maps to avoid per-scope
alloc/rehash (#23761) (Boshen)
- 0b07c4c semantic: Avoid heap alloc for catch-clause binding ids
(#23911) (Lawrence Lin)
- c5eef8b regular_expression: Skip capturing-group pre-parse when
pattern has no `(` (#23908) (Lawrence Lin)
- b4f5b4b isolated_declarations: Remove redundant clone of formal
parameter pattern (#23912) (Lawrence Lin)
- 53d083f isolated_declarations: Use `TakeIn` not `CloneIn` (#23847)
(overlookmotel)
- 3ea9304 react_compiler: Use faster API to arena allocate strings
(#23849) (overlookmotel)
- a6d8e45 parser: Avoid span lookup for arrow expression body (#23788)
(camc314)
- e1886a0 transformer, minifier: Use `static_ident!` macro to create
static `Ident`s (#23727) (overlookmotel)
- 5527bef transformer/object-rest-spread: Reduce iteration (#23720)
(overlookmotel)
- 680ffbc transformer: Allocate AST nodes in arena directly (#23711)
(overlookmotel)
- 1c63c66 parser: Allocate AST nodes in arena directly (#23712)
(overlookmotel)
- 3855f0c minifier: Allocate AST nodes in arena directly (#23710)
(overlookmotel)
- d025887 isolated_declarations: Allocate AST nodes in arena directly
(#23709) (overlookmotel)
- 10b96c6 parser: Remove string search from parsing JSX element name
(#23713) (overlookmotel)

### 📚 Documentation

- 3d61dea all: Correct capitalization in comments (#23887)
(overlookmotel)
- aa1ad74 ast: Add `#[deprecated]` to legacy `AstBuilder` methods
(#23877) (overlookmotel)
- a4676db ast: Correct doc comment for `NONE` (#23765) (overlookmotel)
- 419ec80 syntax: Fix typo in doc comment (#23674) (overlookmotel)

### 🛡️ Security

- 3cdd18f deps: Update npm packages (#23690) (renovate[bot])

Co-authored-by: Boshen <1430279+Boshen@users.noreply.github.com>
Co-authored-by: Cameron <cameron.clark@hey.com>
linyiru added a commit to linyiru/oxc that referenced this pull request Jul 4, 2026
`substitute_template_literal` folded a constant template literal into a string literal
by calling `TemplateLiteral::to_js_string`, which builds a transient `std::String`
(system allocation), then copied it into the arena via `Str::from_cow_in`. So every
folded template paid a system allocation for a string that immediately ends up in the
arena anyway.

This builds the folded string directly in the arena instead:
- a single-quasi template with no interpolations (`` `abc` ``) reuses the cooked arena
  string directly — no allocation at all;
- the general case builds into a pre-sized `ArenaStringBuilder`.

Behaviour is identical: the same all-or-nothing fold, byte-identical output. Same
technique as oxc-project#20386 / oxc-project#23846, applied to a spot that still went through std::String.

`cargo allocs` (minifier system allocations):
  kitchen-sink.tsx  2576 -> 675   (-74%)
  antd.js           1040 -> 339   (-701)
  pdf.mjs           2569 -> 2209
  checker.ts         162 -> 53

Arena allocations rise slightly (the intended std::String -> arena trade-off).
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