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Remove redundant union check in `KnownPanicsLint const prop 

because we are already marking unions `NoPropagation` in
`CanConstProp::check()`. That is enough to prevent any attempts
at const propagating unions and this second check is not needed.

Also improve a comment in `CanConstProp::check()`
This commit is contained in:
Gurinder Singh 2024-04-30 15:17:47 +05:30
parent f9dca46218
commit 741d40f327
1 changed files with 18 additions and 29 deletions
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23
compiler/rustc_mir_transform/src/known_panics_lint.rs
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@ -583,21 +583,10 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
val.into()
}
Aggregate(ref kind, ref fields) => {
// Do not const prop union fields as they can be
// made to produce values that don't match their
// underlying layout's type (see ICE #121534).
// If the last element of the `Adt` tuple
// is `Some` it indicates the ADT is a union
if let AggregateKind::Adt(_, _, _, _, Some(_)) = **kind {
return None;
};
Value::Aggregate {
Aggregate(ref kind, ref fields) => Value::Aggregate {
fields: fields
.iter()
.map(|field| {
self.eval_operand(field).map_or(Value::Uninit, Value::Immediate)
})
.map(|field| self.eval_operand(field).map_or(Value::Uninit, Value::Immediate))
.collect(),
variant: match **kind {
AggregateKind::Adt(_, variant, _, _, _) => variant,
@ -608,8 +597,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
| AggregateKind::Coroutine(_, _)
| AggregateKind::CoroutineClosure(_, _) => VariantIdx::ZERO,
},
}
}
},
Repeat(ref op, n) => {
trace!(?op, ?n);
@ -897,8 +885,9 @@ impl CanConstProp {
for (local, val) in cpv.can_const_prop.iter_enumerated_mut() {
let ty = body.local_decls[local].ty;
if ty.is_union() {
// Do not const prop unions as they can
// ICE during layout calc
// Unions are incompatible with the current implementation of
// const prop because Rust has no concept of an active
// variant of a union
*val = ConstPropMode::NoPropagation;
} else {
match tcx.layout_of(param_env.and(ty)) {