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fix safe-transmute handling of enums

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This commit is contained in:
Ralf Jung 2024-11-30 19:33:23 +01:00
parent a36652c274
commit 611a99188e
7 changed files with 74 additions and 63 deletions
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57
compiler/rustc_transmute/src/layout/tree.rs
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@ -319,38 +319,35 @@ pub(crate) mod rustc {
) -> Result<Self, Err> {
assert!(def.is_enum());
// Computes the variant of a given index.
let layout_of_variant = |index, encoding: Option<TagEncoding<VariantIdx>>| {
let tag = cx.tcx().tag_for_variant((cx.tcx().erase_regions(ty), index));
let variant_def = Def::Variant(def.variant(index));
let variant_layout = ty_variant(cx, (ty, layout), index);
Self::from_variant(
variant_def,
tag.map(|tag| (tag, index, encoding.unwrap())),
(ty, variant_layout),
layout.size,
cx,
)
};
// Computes the layout of a variant.
let layout_of_variant =
|index, encoding: Option<TagEncoding<VariantIdx>>| -> Result<Self, Err> {
let variant_layout = ty_variant(cx, (ty, layout), index);
if variant_layout.is_uninhabited() {
return Ok(Self::uninhabited());
}
let tag = cx.tcx().tag_for_variant((cx.tcx().erase_regions(ty), index));
let variant_def = Def::Variant(def.variant(index));
Self::from_variant(
variant_def,
tag.map(|tag| (tag, index, encoding.unwrap())),
(ty, variant_layout),
layout.size,
cx,
)
};
// We consider three kinds of enums, each demanding a different
// treatment of their layout computation:
// 1. enums that are uninhabited ZSTs
// 2. enums that delegate their layout to a variant
// 3. enums with multiple variants
match layout.variants() {
Variants::Single { .. } if layout.is_uninhabited() && layout.size == Size::ZERO => {
// The layout representation of uninhabited, ZST enums is
// defined to be like that of the `!` type, as opposed of a
// typical enum. Consequently, they cannot be descended into
// as if they typical enums. We therefore special-case this
// scenario and simply return an uninhabited `Tree`.
Ok(Self::uninhabited())
}
Variants::Single { index } => {
// `Variants::Single` on enums with variants denotes that
// the enum delegates its layout to the variant at `index`.
layout_of_variant(*index, None)
// Hilariously, `Single` is used even for 0-variant enums;
// `index` is just junk in that case.
if ty.ty_adt_def().unwrap().variants().is_empty() {
Ok(Self::uninhabited())
} else {
// `Variants::Single` on enums with variants denotes that
// the enum delegates its layout to the variant at `index`.
layout_of_variant(*index, None)
}
}
Variants::Multiple { tag, tag_encoding, tag_field, .. } => {
// `Variants::Multiple` denotes an enum with multiple
@ -369,7 +366,7 @@ pub(crate) mod rustc {
},
)?;
return Ok(Self::def(Def::Adt(def)).then(variants));
Ok(Self::def(Def::Adt(def)).then(variants))
}
}
}