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Merged
kdy1 merged 2 commits into from
Jul 25, 2025
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perf(es/minifier): Use bitflag for var kind #10940

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d9256ba
perf(es/minifier): bitflag for var kind
bvanjoi Jul 25, 2025
dd41f92
Create odd-toes-return.md
kdy1 Jul 25, 2025
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6 changes: 6 additions & 0 deletions .changeset/odd-toes-return.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@
---
swc_ecma_minifier: patch
swc_core: patch
---

perf(es/minifier): bitflag for var kind
78 changes: 43 additions & 35 deletions crates/swc_ecma_minifier/src/compress/optimize/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -73,7 +73,6 @@ pub(super) fn optimizer<'a>(
in_strict: options.module,
remaining_depth: 6,
},
var_kind: None,
scope: SyntaxContext::default(),
bit_ctx: BitCtx::default(),
};
Expand Down Expand Up @@ -101,8 +100,6 @@ pub(super) fn optimizer<'a>(
struct Ctx {
expr_ctx: ExprCtx,

var_kind: Option<VarDeclKind>,

/// Current scope.
scope: SyntaxContext,

Expand All @@ -120,68 +117,75 @@ bitflags! {
#[derive(Debug, Clone, Copy, Default)]
pub(crate) struct BitCtx: u32 {
/// `true` if the [VarDecl] has const annotation.
const HasConstAnn = 1 << 0;
const IsConst = 1 << 0;
const IsVar = 1 << 1;
const IsLet = 1 << 2;

const DontUsePrependNorAppend = 1 << 1;
const DontUsePrependNorAppend = 1 << 3;

const InBoolCtx = 1 << 2;
const InBoolCtx = 1 << 4;

const InAsm = 1 << 3;
const InAsm = 1 << 5;

/// `true` only for [Callee::Expr].
const IsCallee = 1 << 4;
const IsCallee = 1 << 6;

/// `true` if we are try block. `true` means we cannot be sure about control
/// flow.
const InTryBlock = 1 << 5;
const InTryBlock = 1 << 7;

/// `true` while handling `test` of if / while / for.
const InCond = 1 << 6;
const InCond = 1 << 8;

/// `true` if we are in `arg` of `delete arg`.
const IsDeleteArg = 1 << 7;
const IsDeleteArg = 1 << 9;

/// `true` if we are in `arg` of `++arg` or `--arg`.
const IsUpdateArg = 1 << 8;
const IsLhsOfAssign = 1 << 9;
const IsUpdateArg = 1 << 10;

const IsLhsOfAssign = 1 << 11;

/// `false` for `d` in `d[0] = foo`.
const IsExactLhsOfAssign = 1 << 10;
const IsExactLhsOfAssign = 1 << 12;

/// `true` for loop bodies and conditions of loops.
const ExecutedMultipleTime = 1 << 11;
const ExecutedMultipleTime = 1 << 13;

/// `true` while handling `expr` of `!expr`
const InBangArg = 1 << 12;
const InVarDeclOfForInOrOfLoop = 1 << 13;
const InBangArg = 1 << 14;

const InVarDeclOfForInOrOfLoop = 1 << 15;

const DontUseNegatedIife = 1 << 14;
const DontUseNegatedIife = 1 << 16;

/// `true` while handling top-level export decls.
const IsExported = 1 << 15;
const IsExported = 1 << 17;

/// `true` while handling top level items.
const TopLevel = 1 << 16;
const TopLevel = 1 << 18;

/// `true` while we are in a function or something similar.
const InFnLike = 1 << 17;
const InFnLike = 1 << 19;

const InBlock = 1 << 18;
const InBlock = 1 << 20;

const InObjOfNonComputedMember = 1 << 19;
const InObjOfNonComputedMember = 1 << 21;

const InTplExpr = 1 << 20;
const InTplExpr = 1 << 22;

/// True while handling callee, except an arrow expression in callee.
const IsThisAwareCallee = 1 << 21;
const IsThisAwareCallee = 1 << 23;

const IsNestedIfReturnMerging = 1 << 22;
const IsNestedIfReturnMerging = 1 << 24;

const DontInvokeIife = 1 << 23;
const DontInvokeIife = 1 << 25;

const InWithStmt = 1 << 24;
const InWithStmt = 1 << 26;

const InParam = 1 << 25;
const InParam = 1 << 27;

/// `true` while we are inside a class body.
const InClass = 1 << 26;
const InClass = 1 << 28;
}
}

Expand Down Expand Up @@ -2336,7 +2340,6 @@ impl VisitMut for Optimizer<'_> {
fn visit_mut_param(&mut self, n: &mut Param) {
let ctx = Ctx {
bit_ctx: self.ctx.bit_ctx.with(BitCtx::InParam, true),
var_kind: None,
..self.ctx.clone()
};
let mut o = self.with_ctx(ctx);
Expand Down Expand Up @@ -2769,8 +2772,9 @@ impl VisitMut for Optimizer<'_> {
.ctx
.bit_ctx
.with(BitCtx::IsUpdateArg, false)
.with(BitCtx::HasConstAnn, false),
var_kind: None,
.with(BitCtx::IsConst, false)
.with(BitCtx::IsLet, false)
.with(BitCtx::IsVar, false),
..self.ctx.clone()
};

Expand All @@ -2787,8 +2791,12 @@ impl VisitMut for Optimizer<'_> {
.ctx
.bit_ctx
.with(BitCtx::IsUpdateArg, false)
.with(BitCtx::HasConstAnn, self.has_const_ann(n.ctxt)),
var_kind: Some(n.kind),
.with(
BitCtx::IsConst,
n.kind == VarDeclKind::Const || self.has_const_ann(n.ctxt),
)
.with(BitCtx::IsVar, n.kind == VarDeclKind::Var)
.with(BitCtx::IsLet, n.kind == VarDeclKind::Let),
..self.ctx.clone()
};

Expand Down
24 changes: 18 additions & 6 deletions crates/swc_ecma_minifier/src/compress/optimize/unused.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -71,10 +71,14 @@ impl Optimizer<'_> {

#[cfg(debug_assertions)]
{
if let Some(VarDeclKind::Const | VarDeclKind::Let) = self.ctx.var_kind {
if had_init && var.init.is_none() {
unreachable!("const/let variable without initializer: {:#?}", var);
}
if self
.ctx
.bit_ctx
.intersects(BitCtx::IsConst.union(BitCtx::IsLet))
&& had_init
&& var.init.is_none()
{
unreachable!("const/let variable without initializer: {:#?}", var);
}
}
}
Expand Down Expand Up @@ -202,7 +206,11 @@ impl Optimizer<'_> {

if v.ref_count == 0 && v.usage_count == 0 {
if let Some(e) = init {
if let Some(VarDeclKind::Const | VarDeclKind::Let) = self.ctx.var_kind {
if self
.ctx
.bit_ctx
.intersects(BitCtx::IsConst.union(BitCtx::IsLet))
{
if let Expr::Lit(Lit::Null(..)) = e {
return;
}
Expand All @@ -212,7 +220,11 @@ impl Optimizer<'_> {
if let Some(ret) = ret {
*e = ret;
} else {
if let Some(VarDeclKind::Const | VarDeclKind::Let) = self.ctx.var_kind {
if self
.ctx
.bit_ctx
.intersects(BitCtx::IsConst.union(BitCtx::IsLet))
{
*e = Null { span: DUMMY_SP }.into();
} else {
*e = Invalid { span: DUMMY_SP }.into();
Expand Down
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