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fix: 🐛 Don't fold operand before a unary consumer #173

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Merged
chikuwait merged 1 commit into from
Jun 10, 2026
Merged

fix: 🐛 Don't fold operand before a unary consumer #173

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43 changes: 39 additions & 4 deletions src/parser.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -153,6 +153,41 @@ fn take_f64_operand(
}
}

/// Check if `op` is a *unary* foldable consumer (consumes exactly one operand).
///
/// The two-ahead fold in `can_fold_*` assumes the consumer is binary and takes
/// both preceding values. A unary consumer (e.g. `i64.eqz`) takes only one, so
/// folding the other leaves a phantom register later reads as garbage. Exclude
/// them so that value stays materialized.
#[inline]
fn is_unary_foldable_consumer(op: &wasmparser::Operator) -> bool {
matches!(
op,
wasmparser::Operator::I32Clz
| wasmparser::Operator::I32Ctz
| wasmparser::Operator::I32Popcnt
| wasmparser::Operator::I32Eqz
| wasmparser::Operator::I64Clz
| wasmparser::Operator::I64Ctz
| wasmparser::Operator::I64Popcnt
| wasmparser::Operator::I64Eqz
| wasmparser::Operator::F32Abs
| wasmparser::Operator::F32Neg
| wasmparser::Operator::F32Ceil
| wasmparser::Operator::F32Floor
| wasmparser::Operator::F32Trunc
| wasmparser::Operator::F32Nearest
| wasmparser::Operator::F32Sqrt
| wasmparser::Operator::F64Abs
| wasmparser::Operator::F64Neg
| wasmparser::Operator::F64Ceil
| wasmparser::Operator::F64Floor
| wasmparser::Operator::F64Trunc
| wasmparser::Operator::F64Nearest
| wasmparser::Operator::F64Sqrt
)
}

/// Check if the next instruction(s) can fold an I32 operand.
#[inline]
fn can_fold_i32<'a>(
Expand All @@ -168,7 +203,7 @@ fn can_fold_i32<'a>(
wasmparser::Operator::I32Const { .. } | wasmparser::Operator::LocalGet { .. }
) {
if let Some(Ok((next_next_op, _))) = ops.peek() {
is_i32_foldable_consumer(next_next_op)
is_i32_foldable_consumer(next_next_op) && !is_unary_foldable_consumer(next_next_op)
} else {
false
}
Expand Down Expand Up @@ -197,7 +232,7 @@ fn can_fold_i64<'a>(
wasmparser::Operator::I64Const { .. } | wasmparser::Operator::LocalGet { .. }
) {
if let Some(Ok((next_next_op, _))) = ops.peek() {
is_i64_foldable_consumer(next_next_op)
is_i64_foldable_consumer(next_next_op) && !is_unary_foldable_consumer(next_next_op)
} else {
false
}
Expand Down Expand Up @@ -226,7 +261,7 @@ fn can_fold_f32<'a>(
wasmparser::Operator::F32Const { .. } | wasmparser::Operator::LocalGet { .. }
) {
if let Some(Ok((next_next_op, _))) = ops.peek() {
is_f32_foldable_consumer(next_next_op)
is_f32_foldable_consumer(next_next_op) && !is_unary_foldable_consumer(next_next_op)
} else {
false
}
Expand Down Expand Up @@ -255,7 +290,7 @@ fn can_fold_f64<'a>(
wasmparser::Operator::F64Const { .. } | wasmparser::Operator::LocalGet { .. }
) {
if let Some(Ok((next_next_op, _))) = ops.peek() {
is_f64_foldable_consumer(next_next_op)
is_f64_foldable_consumer(next_next_op) && !is_unary_foldable_consumer(next_next_op)
} else {
false
}
Expand Down
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