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const_eval and codegen: audit uses of is_zst

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This commit is contained in:
Ralf Jung 2023-08-27 18:12:34 +02:00
parent bf91321e0f
commit b2ebf1c23f
12 changed files with 42 additions and 29 deletions
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20
compiler/rustc_const_eval/src/interpret/cast.rs
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@ -410,21 +410,25 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
self.unsize_into_ptr(src, dest, *s, *c)
}
(&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => {
assert_eq!(def_a, def_b);
assert_eq!(def_a, def_b); // implies same number of fields
// 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
// Unsizing of generic struct with pointer fields, like `Arc<T>` -> `Arc<Trait>`.
// There can be extra fields as long as they don't change their type or are 1-ZST.
// There might also be no field that actually needs unsizing.
let mut found_cast_field = false;
for i in 0..src.layout.fields.count() {
let cast_ty_field = cast_ty.field(self, i);
if cast_ty_field.is_zst() {
continue;
}
let src_field = self.project_field(src, i)?;
let dst_field = self.project_field(dest, i)?;
if src_field.layout.ty == cast_ty_field.ty {
if src_field.layout.is_1zst() && cast_ty_field.is_1zst() {
// Skip 1-ZST fields.
} else if src_field.layout.ty == cast_ty_field.ty {
self.copy_op(&src_field, &dst_field, /*allow_transmute*/ false)?;
} else {
if found_cast_field {
span_bug!(self.cur_span(), "unsize_into: more than one field to cast");
}
found_cast_field = true;
self.unsize_into(&src_field, cast_ty_field, &dst_field)?;
}
}