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Aug 11, 2025
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refactor(minifier): change AST in-place instead of returning Option<Expression> #12993

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156 changes: 68 additions & 88 deletions crates/oxc_minifier/src/peephole/minimize_conditions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,46 +20,26 @@ impl<'a> PeepholeOptimizations {
expr: &mut Expression<'a>,
ctx: &mut Ctx<'a, '_>,
) {
let mut changed = false;
loop {
let mut local_change = false;
if let Some(folded_expr) = match expr {
Expression::UnaryExpression(e) => self.try_minimize_not(e, ctx),
Expression::BinaryExpression(e) => {
if Self::try_compress_is_loose_boolean(e, ctx) {
local_change = true;
}
Self::try_minimize_binary(e, ctx)
}
Expression::LogicalExpression(e) => self.minimize_logical_expression(e, ctx),
Expression::ConditionalExpression(logical_expr) => {
if self.try_fold_expr_in_boolean_context(&mut logical_expr.test, ctx) {
local_change = true;
}
self.try_minimize_conditional(logical_expr, ctx)
}
Expression::AssignmentExpression(e) => {
if self.try_compress_normal_assignment_to_combined_logical_assignment(e, ctx) {
local_change = true;
}
if Self::try_compress_normal_assignment_to_combined_assignment(e, ctx) {
local_change = true;
}
Self::try_compress_assignment_to_update_expression(e, ctx)
match expr {
Expression::UnaryExpression(_) => self.try_minimize_not(expr, ctx),
Expression::BinaryExpression(e) => {
Self::try_compress_is_loose_boolean(e, ctx);
Self::try_minimize_binary(expr, ctx);
}
Expression::LogicalExpression(_) => self.minimize_logical_expression(expr, ctx),
Expression::ConditionalExpression(logical_expr) => {
self.try_fold_expr_in_boolean_context(&mut logical_expr.test, ctx);
if let Some(changed) = self.try_minimize_conditional(logical_expr, ctx) {
*expr = changed;
ctx.state.changed = true;
}
_ => None,
} {
*expr = folded_expr;
local_change = true;
}
if local_change {
changed = true;
} else {
break;
Expression::AssignmentExpression(e) => {
self.try_compress_normal_assignment_to_combined_logical_assignment(e, ctx);
Self::try_compress_normal_assignment_to_combined_assignment(e, ctx);
Self::try_compress_assignment_to_update_expression(expr, ctx);
}
}
if changed {
ctx.state.changed = true;
_ => {}
}
}

Expand Down Expand Up @@ -103,9 +83,9 @@ impl<'a> PeepholeOptimizations {
}
// "a op b" => "a op b"
// "(a op b) op c" => "(a op b) op c"
let mut logic_expr = ctx.ast.logical_expression(span, a, op, b);
self.minimize_logical_expression(&mut logic_expr, ctx)
.unwrap_or_else(|| Expression::LogicalExpression(ctx.ast.alloc(logic_expr)))
let mut logic_expr = ctx.ast.expression_logical(span, a, op, b);
self.minimize_logical_expression(&mut logic_expr, ctx);
logic_expr
}

// `typeof foo === 'number'` -> `typeof foo == 'number'`
Expand All @@ -115,17 +95,15 @@ impl<'a> PeepholeOptimizations {
// ^^^^^^^^^^^^^^ `ctx.expression_value_type(&e.left).is_boolean()` is `true`.
// `x >> +y !== 0` -> `x >> +y`
// ^^^^^^^ ctx.expression_value_type(&e.left).is_number()` is `true`.
fn try_minimize_binary(
e: &mut BinaryExpression<'a>,
ctx: &mut Ctx<'a, '_>,
) -> Option<Expression<'a>> {
fn try_minimize_binary(expr: &mut Expression<'a>, ctx: &mut Ctx<'a, '_>) {
let Expression::BinaryExpression(e) = expr else { return };
if !e.operator.is_equality() {
return None;
return;
}
let left = e.left.value_type(ctx);
let right = e.right.value_type(ctx);
if left.is_undetermined() || right.is_undetermined() {
return None;
return;
}
if left == right {
match e.operator {
Expand All @@ -139,12 +117,14 @@ impl<'a> PeepholeOptimizations {
}
}
if !left.is_boolean() {
return None;
return;
}
if e.right.may_have_side_effects(ctx) {
return None;
return;
}
let mut b = e.right.evaluate_value(ctx).and_then(ConstantValue::into_boolean)?;
let Some(mut b) = e.right.evaluate_value(ctx).and_then(ConstantValue::into_boolean) else {
return;
};
match e.operator {
BinaryOperator::Inequality | BinaryOperator::StrictInequality => {
e.operator = BinaryOperator::Equality;
Expand All @@ -154,14 +134,15 @@ impl<'a> PeepholeOptimizations {
e.operator = BinaryOperator::Equality;
}
BinaryOperator::Equality => {}
_ => return None,
_ => return,
}
Some(if b {
*expr = if b {
e.left.take_in(ctx.ast)
} else {
let argument = e.left.take_in(ctx.ast);
ctx.ast.expression_unary(e.span, UnaryOperator::LogicalNot, argument)
})
};
ctx.state.changed = true;
}

/// Compress `foo == true` into `foo == 1`.
Expand All @@ -171,19 +152,19 @@ impl<'a> PeepholeOptimizations {
///
/// In `IsLooselyEqual`, `true` and `false` are converted to `1` and `0` first.
/// <https://tc39.es/ecma262/multipage/abstract-operations.html#sec-islooselyequal>
fn try_compress_is_loose_boolean(e: &mut BinaryExpression<'a>, ctx: &mut Ctx<'a, '_>) -> bool {
fn try_compress_is_loose_boolean(e: &mut BinaryExpression<'a>, ctx: &mut Ctx<'a, '_>) {
if !matches!(e.operator, BinaryOperator::Equality | BinaryOperator::Inequality) {
return false;
return;
}

if let Some(ConstantValue::Boolean(left_bool)) = e.left.evaluate_value(ctx) {
e.left = ctx.ast.expression_numeric_literal(
e.left.span(),
if left_bool { 1.0 } else { 0.0 },
None,
NumberBase::Decimal,
);
return true;
ctx.state.changed = true;
return;
}
if let Some(ConstantValue::Boolean(right_bool)) = e.right.evaluate_value(ctx) {
e.right = ctx.ast.expression_numeric_literal(
Expand All @@ -192,9 +173,8 @@ impl<'a> PeepholeOptimizations {
None,
NumberBase::Decimal,
);
return true;
ctx.state.changed = true;
}
false
}

/// Returns the identifier or the assignment target's identifier of the given expression.
Expand Down Expand Up @@ -222,15 +202,15 @@ impl<'a> PeepholeOptimizations {
&self,
expr: &mut AssignmentExpression<'a>,
ctx: &mut Ctx<'a, '_>,
) -> bool {
) {
if ctx.options().target < ESTarget::ES2020 {
return false;
return;
}
if !matches!(expr.operator, AssignmentOperator::Assign) {
return false;
return;
}

let Expression::LogicalExpression(logical_expr) = &mut expr.right else { return false };
let Expression::LogicalExpression(logical_expr) = &mut expr.right else { return };
// NOTE: if the right hand side is an anonymous function, applying this compression will
// set the `name` property of that function.
// Since codes relying on the fact that function's name is undefined should be rare,
Expand All @@ -241,64 +221,64 @@ impl<'a> PeepholeOptimizations {
Expression::Identifier(read_id_ref),
) = (&expr.left, &logical_expr.left)
else {
return false;
return;
};
// It should also early return when the reference might refer to a reference value created by a with statement
// when the minifier supports with statements
if write_id_ref.name != read_id_ref.name || ctx.is_global_reference(write_id_ref) {
return false;
return;
}

let new_op = logical_expr.operator.to_assignment_operator();
expr.operator = new_op;
expr.right = logical_expr.right.take_in(ctx.ast);
true
ctx.state.changed = true;
}

/// Compress `a = a + b` to `a += b`
fn try_compress_normal_assignment_to_combined_assignment(
expr: &mut AssignmentExpression<'a>,
ctx: &mut Ctx<'a, '_>,
) -> bool {
) {
if !matches!(expr.operator, AssignmentOperator::Assign) {
return false;
return;
}

let Expression::BinaryExpression(binary_expr) = &mut expr.right else { return false };
let Some(new_op) = binary_expr.operator.to_assignment_operator() else { return false };

let Expression::BinaryExpression(binary_expr) = &mut expr.right else { return };
let Some(new_op) = binary_expr.operator.to_assignment_operator() else { return };
if !Self::has_no_side_effect_for_evaluation_same_target(&expr.left, &binary_expr.left, ctx)
{
return false;
return;
}

expr.operator = new_op;
expr.right = binary_expr.right.take_in(ctx.ast);
true
ctx.state.changed = true;
}

/// Compress `a -= 1` to `--a` and `a -= -1` to `++a`
#[expect(clippy::float_cmp)]
fn try_compress_assignment_to_update_expression(
expr: &mut AssignmentExpression<'a>,
expr: &mut Expression<'a>,
ctx: &mut Ctx<'a, '_>,
) -> Option<Expression<'a>> {
if !matches!(expr.operator, AssignmentOperator::Subtraction) {
return None;
) {
let Expression::AssignmentExpression(e) = expr else { return };
if !matches!(e.operator, AssignmentOperator::Subtraction) {
return;
}
let Expression::NumericLiteral(num) = &expr.right else {
return None;
};
let target = expr.left.as_simple_assignment_target_mut()?;
let operator = if num.value == 1.0 {
UpdateOperator::Decrement
} else if num.value == -1.0 {
UpdateOperator::Increment
let operator = if let Expression::NumericLiteral(num) = &e.right {
if num.value == 1.0 {
UpdateOperator::Decrement
} else if num.value == -1.0 {
UpdateOperator::Increment
} else {
return;
}
} else {
return None;
return;
};
let Some(target) = e.left.as_simple_assignment_target_mut() else { return };
let target = target.take_in(ctx.ast);
Some(ctx.ast.expression_update(expr.span, operator, true, target))
*expr = ctx.ast.expression_update(e.span, operator, true, target);
ctx.state.changed = true;
}
}

Expand Down
18 changes: 9 additions & 9 deletions crates/oxc_minifier/src/peephole/minimize_expression_in_boolean_context.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,7 @@ impl<'a> PeepholeOptimizations {
&self,
expr: &mut Expression<'a>,
ctx: &mut Ctx<'a, '_>,
) -> bool {
) {
match expr {
// "!!a" => "a"
Expression::UnaryExpression(u1) if u1.operator.is_not() => {
Expand All @@ -42,7 +42,7 @@ impl<'a> PeepholeOptimizations {
let mut e = u2.argument.take_in(ctx.ast);
self.try_fold_expr_in_boolean_context(&mut e, ctx);
*expr = e;
return true;
ctx.state.changed = true;
}
}
}
Expand All @@ -62,7 +62,7 @@ impl<'a> PeepholeOptimizations {
// `if ((a | b) === 0);", "if (!(a | b));")`
ctx.ast.expression_unary(e.span, UnaryOperator::LogicalNot, argument)
};
return true;
ctx.state.changed = true;
}
// "if (!!a && !!b)" => "if (a && b)"
Expression::LogicalExpression(e) if e.operator.is_and() => {
Expand All @@ -71,7 +71,7 @@ impl<'a> PeepholeOptimizations {
// "if (anything && truthyNoSideEffects)" => "if (anything)"
if e.right.get_side_free_boolean_value(ctx) == Some(true) {
*expr = e.left.take_in(ctx.ast);
return true;
ctx.state.changed = true;
}
}
// "if (!!a ||!!b)" => "if (a || b)"
Expand All @@ -81,7 +81,7 @@ impl<'a> PeepholeOptimizations {
// "if (anything || falsyNoSideEffects)" => "if (anything)"
if e.right.get_side_free_boolean_value(ctx) == Some(false) {
*expr = e.left.take_in(ctx.ast);
return true;
ctx.state.changed = true;
}
}
Expression::ConditionalExpression(e) => {
Expand All @@ -100,7 +100,8 @@ impl<'a> PeepholeOptimizations {
(LogicalOperator::And, self.minimize_not(left.span(), left, ctx))
};
*expr = self.join_with_left_associative_op(span, op, left, right, ctx);
return true;
ctx.state.changed = true;
return;
}
if let Some(boolean) = e.alternate.get_side_free_boolean_value(ctx) {
let left = e.test.take_in(ctx.ast);
Expand All @@ -114,17 +115,16 @@ impl<'a> PeepholeOptimizations {
(LogicalOperator::And, left)
};
*expr = self.join_with_left_associative_op(span, op, left, right, ctx);
return true;
ctx.state.changed = true;
}
}
Expression::SequenceExpression(seq_expr) => {
if let Some(last) = seq_expr.expressions.last_mut() {
return self.try_fold_expr_in_boolean_context(last, ctx);
self.try_fold_expr_in_boolean_context(last, ctx);
}
}
_ => {}
}
false
}
}

Expand Down
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