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Fix unsizing casts
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RalfJung committed May 24, 2020
1 parent b97ed1a commit b9b1554
Showing 1 changed file with 18 additions and 20 deletions.
38 changes: 18 additions & 20 deletions src/librustc_mir/interpret/cast.rs
Expand Up @@ -25,12 +25,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
// FIXME: In which cases should we trigger UB when the source is uninit?
match cast_kind {
Pointer(PointerCast::Unsize) => {
assert_eq!(
cast_ty, dest.layout.ty,
"mismatch of cast type {} and place type {}",
cast_ty, dest.layout.ty
);
self.unsize_into(src, dest)?;
let cast_ty = self.layout_of(cast_ty)?;
self.unsize_into(src, cast_ty, dest)?;
}

Misc => {
Expand Down Expand Up @@ -266,11 +262,11 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
dest: PlaceTy<'tcx, M::PointerTag>,
// The pointee types
source_ty: Ty<'tcx>,
dest_ty: Ty<'tcx>,
cast_ty: Ty<'tcx>,
) -> InterpResult<'tcx> {
// A<Struct> -> A<Trait> conversion
let (src_pointee_ty, dest_pointee_ty) =
self.tcx.struct_lockstep_tails_erasing_lifetimes(source_ty, dest_ty, self.param_env);
self.tcx.struct_lockstep_tails_erasing_lifetimes(source_ty, cast_ty, self.param_env);

match (&src_pointee_ty.kind, &dest_pointee_ty.kind) {
(&ty::Array(_, length), &ty::Slice(_)) => {
Expand Down Expand Up @@ -298,48 +294,50 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
self.write_immediate(val, dest)
}

_ => bug!("invalid unsizing {:?} -> {:?}", src.layout.ty, dest.layout.ty),
_ => bug!("invalid unsizing {:?} -> {:?}", src.layout.ty, cast_ty),
}
}

fn unsize_into(
&mut self,
src: OpTy<'tcx, M::PointerTag>,
cast_ty: TyAndLayout<'tcx>,
dest: PlaceTy<'tcx, M::PointerTag>,
) -> InterpResult<'tcx> {
trace!("Unsizing {:?} of type {} into {:?}", *src, src.layout.ty, dest.layout.ty);
match (&src.layout.ty.kind, &dest.layout.ty.kind) {
(&ty::Ref(_, s, _), &ty::Ref(_, d, _) | &ty::RawPtr(TypeAndMut { ty: d, .. }))
| (&ty::RawPtr(TypeAndMut { ty: s, .. }), &ty::RawPtr(TypeAndMut { ty: d, .. })) => {
self.unsize_into_ptr(src, dest, s, d)
trace!("Unsizing {:?} of type {} into {:?}", *src, src.layout.ty, cast_ty.ty);
match (&src.layout.ty.kind, &cast_ty.ty.kind) {
(&ty::Ref(_, s, _), &ty::Ref(_, c, _) | &ty::RawPtr(TypeAndMut { ty: c, .. }))
| (&ty::RawPtr(TypeAndMut { ty: s, .. }), &ty::RawPtr(TypeAndMut { ty: c, .. })) => {
self.unsize_into_ptr(src, dest, s, c)
}
(&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => {
assert_eq!(def_a, def_b);
if def_a.is_box() || def_b.is_box() {
if !def_a.is_box() || !def_b.is_box() {
bug!("invalid unsizing between {:?} -> {:?}", src.layout, dest.layout);
bug!("invalid unsizing between {:?} -> {:?}", src.layout.ty, cast_ty.ty);
}
return self.unsize_into_ptr(
src,
dest,
src.layout.ty.boxed_ty(),
dest.layout.ty.boxed_ty(),
cast_ty.ty.boxed_ty(),
);
}

// unsizing of generic struct with pointer fields
// Example: `Arc<T>` -> `Arc<Trait>`
// here we need to increase the size of every &T thin ptr field to a fat ptr
for i in 0..src.layout.fields.count() {
let dst_field = self.place_field(dest, i)?;
if dst_field.layout.is_zst() {
let cast_ty_field = cast_ty.field(self, i)?;
if cast_ty_field.is_zst() {
continue;
}
let src_field = self.operand_field(src, i)?;
if src_field.layout.ty == dst_field.layout.ty {
let dst_field = self.place_field(dest, i)?;
if src_field.layout.ty == cast_ty_field.ty {
self.copy_op(src_field, dst_field)?;
} else {
self.unsize_into(src_field, dst_field)?;
self.unsize_into(src_field, cast_ty_field, dst_field)?;
}
}
Ok(())
Expand Down

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