bjoernager/rust
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Fix unsound optimization with explicit variant discriminants

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This commit is contained in:
Fabian Wolff 2021-10-03 15:29:56 +02:00
parent edebf77e00
commit 529c35331b
2 changed files with 32 additions and 4 deletions
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18
compiler/rustc_mir_transform/src/simplify_try.rs
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@ -706,12 +706,22 @@ impl<'a, 'tcx> SimplifyBranchSameOptimizationFinder<'a, 'tcx> {
let helper = |rhs: &Rvalue<'tcx>,
place: &Place<'tcx>,
variant_index: &VariantIdx,
switch_value: u128,
side_to_choose| {
let place_type = place.ty(self.body, self.tcx).ty;
let adt = match *place_type.kind() {
ty::Adt(adt, _) if adt.is_enum() => adt,
_ => return StatementEquality::NotEqual,
};
let variant_discr = adt.discriminant_for_variant(self.tcx, *variant_index).val;
if variant_discr != switch_value {
trace!(
"NO: variant discriminant {} does not equal switch value {}",
variant_discr,
switch_value
);
return StatementEquality::NotEqual;
}
let variant_is_fieldless = adt.variants[*variant_index].fields.is_empty();
if !variant_is_fieldless {
trace!("NO: variant {:?} was not fieldless", variant_index);
@ -742,18 +752,18 @@ impl<'a, 'tcx> SimplifyBranchSameOptimizationFinder<'a, 'tcx> {
StatementKind::SetDiscriminant { place, variant_index },
)
// we need to make sure that the switch value that targets the bb with SetDiscriminant (y), is the same as the variant index
if Some(variant_index.index() as u128) == y_target_and_value.value => {
if y_target_and_value.value.is_some() => {
// choose basic block of x, as that has the assign
helper(rhs, place, variant_index, x_target_and_value.target)
helper(rhs, place, variant_index, y_target_and_value.value.unwrap(), x_target_and_value.target)
}
(
StatementKind::SetDiscriminant { place, variant_index },
StatementKind::Assign(box (_, rhs)),
)
// we need to make sure that the switch value that targets the bb with SetDiscriminant (x), is the same as the variant index
if Some(variant_index.index() as u128) == x_target_and_value.value => {
if x_target_and_value.value.is_some() => {
// choose basic block of y, as that has the assign
helper(rhs, place, variant_index, y_target_and_value.target)
helper(rhs, place, variant_index, x_target_and_value.value.unwrap(), y_target_and_value.target)
}
_ => {
trace!("NO: statements `{:?}` and `{:?}` not considered equal", x, y);