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Rollup merge of #133702 - RalfJung:single-variant, r=oli-obk

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Variants::Single: do not use invalid VariantIdx for uninhabited enums

~~Stacked on top of https://github.com/rust-lang/rust/pull/133681, only the last commit is new.~~

Currently, `Variants::Single` for an empty enum contains a `VariantIdx` of 0; looking that up in the enum variant list will ICE. That's quite confusing. So let's fix that by adding a new `Variants::Empty` case for types that have 0 variants.

try-job: i686-msvc
This commit is contained in:
许杰友 Jieyou Xu (Joe) 2024-12-19 16:48:07 +08:00 • committed by GitHub
commit 2a43ce03fb
No known key found for this signature in database
GPG key ID: B5690EEEBB952194
33 changed files with 186 additions and 165 deletions
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2
compiler/rustc_abi/src/callconv.rs
View file

@ -206,7 +206,7 @@ impl<'a, Ty> TyAndLayout<'a, Ty> {
let (mut result, mut total) = from_fields_at(*self, Size::ZERO)?;
match &self.variants {
abi::Variants::Single { .. } => {}
abi::Variants::Single { .. } | abi::Variants::Empty => {}
abi::Variants::Multiple { variants, .. } => {
// Treat enum variants like union members.
// HACK(eddyb) pretend the `enum` field (discriminant)

7
compiler/rustc_abi/src/layout.rs
View file

@ -213,8 +213,9 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
&self,
) -> LayoutData<FieldIdx, VariantIdx> {
let dl = self.cx.data_layout();
// This is also used for uninhabited enums, so we use `Variants::Empty`.
LayoutData {
variants: Variants::Single { index: VariantIdx::new(0) },
variants: Variants::Empty,
fields: FieldsShape::Primitive,
backend_repr: BackendRepr::Uninhabited,
largest_niche: None,
@ -1004,8 +1005,8 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
Variants::Multiple { tag, tag_encoding, tag_field, .. } => {
Variants::Multiple { tag, tag_encoding, tag_field, variants: best_layout.variants }
}
Variants::Single { .. } => {
panic!("encountered a single-variant enum during multi-variant layout")
Variants::Single { .. } | Variants::Empty => {
panic!("encountered a single-variant or empty enum during multi-variant layout")
}
};
Ok(best_layout.layout)

6
compiler/rustc_abi/src/lib.rs
View file

@ -1504,10 +1504,12 @@ impl BackendRepr {
#[derive(PartialEq, Eq, Hash, Clone, Debug)]
#[cfg_attr(feature = "nightly", derive(HashStable_Generic))]
pub enum Variants<FieldIdx: Idx, VariantIdx: Idx> {
/// A type with no valid variants. Must be uninhabited.
Empty,
/// Single enum variants, structs/tuples, unions, and all non-ADTs.
Single {
/// Always 0 for non-enums/generators.
/// For enums without a variant, this is an invalid index!
/// Always `0` for types that cannot have multiple variants.
index: VariantIdx,
},

2
compiler/rustc_codegen_cranelift/src/discriminant.rs
View file

@ -18,6 +18,7 @@ pub(crate) fn codegen_set_discriminant<'tcx>(
return;
}
match layout.variants {
Variants::Empty => unreachable!("we already handled uninhabited types"),
Variants::Single { index } => {
assert_eq!(index, variant_index);
}
@ -85,6 +86,7 @@ pub(crate) fn codegen_get_discriminant<'tcx>(
}
let (tag_scalar, tag_field, tag_encoding) = match &layout.variants {
Variants::Empty => unreachable!("we already handled uninhabited types"),
Variants::Single { index } => {
let discr_val = layout
.ty

25
compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/cpp_like.rs
View file

@ -212,21 +212,17 @@ pub(super) fn build_enum_type_di_node<'ll, 'tcx>(
),
|cx, enum_type_di_node| {
match enum_type_and_layout.variants {
Variants::Single { index: variant_index } => {
if enum_adt_def.variants().is_empty() {
// Uninhabited enums have Variants::Single. We don't generate
// any members for them.
return smallvec![];
}
build_single_variant_union_fields(
cx,
enum_adt_def,
enum_type_and_layout,
enum_type_di_node,
variant_index,
)
Variants::Empty => {
// We don't generate any members for uninhabited types.
return smallvec![];
}
Variants::Single { index: variant_index } => build_single_variant_union_fields(
cx,
enum_adt_def,
enum_type_and_layout,
enum_type_di_node,
variant_index,
),
Variants::Multiple {
tag_encoding: TagEncoding::Direct,
ref variants,
@ -303,6 +299,7 @@ pub(super) fn build_coroutine_di_node<'ll, 'tcx>(
)
}
Variants::Single { .. }
| Variants::Empty
| Variants::Multiple { tag_encoding: TagEncoding::Niche { .. }, .. } => {
bug!(
"Encountered coroutine with non-direct-tag layout: {:?}",

2
compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/mod.rs
View file

@ -392,7 +392,7 @@ fn compute_discriminant_value<'ll, 'tcx>(
variant_index: VariantIdx,
) -> DiscrResult {
match enum_type_and_layout.layout.variants() {
&Variants::Single { .. } => DiscrResult::NoDiscriminant,
&Variants::Single { .. } | &Variants::Empty => DiscrResult::NoDiscriminant,
&Variants::Multiple { tag_encoding: TagEncoding::Direct, .. } => DiscrResult::Value(
enum_type_and_layout.ty.discriminant_for_variant(cx.tcx, variant_index).unwrap().val,
),

4
compiler/rustc_codegen_llvm/src/debuginfo/metadata/enums/native.rs
View file

@ -358,8 +358,8 @@ fn build_discr_member_di_node<'ll, 'tcx>(
let containing_scope = enum_or_coroutine_type_di_node;
match enum_or_coroutine_type_and_layout.layout.variants() {
// A single-variant enum has no discriminant.
&Variants::Single { .. } => None,
// A single-variant or no-variant enum has no discriminant.
&Variants::Single { .. } | &Variants::Empty => None,
&Variants::Multiple { tag_field, .. } => {
let tag_base_type = tag_base_type(cx.tcx, enum_or_coroutine_type_and_layout);

2
compiler/rustc_codegen_llvm/src/type_of.rs
View file

@ -38,7 +38,7 @@ fn uncached_llvm_type<'a, 'tcx>(
if let (&ty::Adt(def, _), &Variants::Single { index }) =
(layout.ty.kind(), &layout.variants)
{
if def.is_enum() && !def.variants().is_empty() {
if def.is_enum() {
write!(&mut name, "::{}", def.variant(index).name).unwrap();
}
}

4
compiler/rustc_codegen_ssa/src/debuginfo/mod.rs
View file

@ -65,8 +65,8 @@ fn tag_base_type_opt<'tcx>(
});
match enum_type_and_layout.layout.variants() {
// A single-variant enum has no discriminant.
Variants::Single { .. } => None,
// A single-variant or no-variant enum has no discriminant.
Variants::Single { .. } | Variants::Empty => None,
Variants::Multiple { tag_encoding: TagEncoding::Niche { .. }, tag, .. } => {
// Niche tags are always normalized to unsized integers of the correct size.

7
compiler/rustc_codegen_ssa/src/mir/place.rs
View file

@ -243,6 +243,7 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
return bx.cx().const_poison(cast_to);
}
let (tag_scalar, tag_encoding, tag_field) = match self.layout.variants {
Variants::Empty => unreachable!("we already handled uninhabited types"),
Variants::Single { index } => {
let discr_val = self
.layout
@ -365,9 +366,9 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
return;
}
match self.layout.variants {
Variants::Single { index } => {
assert_eq!(index, variant_index);
}
Variants::Empty => unreachable!("we already handled uninhabited types"),
Variants::Single { index } => assert_eq!(index, variant_index),
Variants::Multiple { tag_encoding: TagEncoding::Direct, tag_field, .. } => {
let ptr = self.project_field(bx, tag_field);
let to =

25
compiler/rustc_const_eval/src/interpret/discriminant.rs
View file

@ -44,7 +44,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
}
}
/// Read discriminant, return the runtime value as well as the variant index.
/// Read discriminant, return the variant index.
/// Can also legally be called on non-enums (e.g. through the discriminant_value intrinsic)!
///
/// Will never return an uninhabited variant.
@ -65,21 +65,17 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
// We use "tag" to refer to how the discriminant is encoded in memory, which can be either
// straight-forward (`TagEncoding::Direct`) or with a niche (`TagEncoding::Niche`).
let (tag_scalar_layout, tag_encoding, tag_field) = match op.layout().variants {
Variants::Empty => {
throw_ub!(UninhabitedEnumVariantRead(None));
}
Variants::Single { index } => {
// Do some extra checks on enums.
if ty.is_enum() {
// Hilariously, `Single` is used even for 0-variant enums.
// (See https://github.com/rust-lang/rust/issues/89765).
if ty.ty_adt_def().unwrap().variants().is_empty() {
throw_ub!(UninhabitedEnumVariantRead(index))
}
if op.layout().is_uninhabited() {
// For consistency with `write_discriminant`, and to make sure that
// `project_downcast` cannot fail due to strange layouts, we declare immediate UB
// for uninhabited variants.
if op.layout().for_variant(self, index).is_uninhabited() {
throw_ub!(UninhabitedEnumVariantRead(index))
}
// for uninhabited enums.
throw_ub!(UninhabitedEnumVariantRead(Some(index)));
}
// Since the type is inhabited, there must be an index.
return interp_ok(index);
}
Variants::Multiple { tag, ref tag_encoding, tag_field, .. } => {
@ -199,11 +195,13 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
// `uninhabited_enum_branching` MIR pass. It also ensures consistency with
// `write_discriminant`.
if op.layout().for_variant(self, index).is_uninhabited() {
throw_ub!(UninhabitedEnumVariantRead(index))
throw_ub!(UninhabitedEnumVariantRead(Some(index)))
}
interp_ok(index)
}
/// Read discriminant, return the user-visible discriminant.
/// Can also legally be called on non-enums (e.g. through the discriminant_value intrinsic)!
pub fn discriminant_for_variant(
&self,
ty: Ty<'tcx>,
@ -243,6 +241,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
}
match layout.variants {
abi::Variants::Empty => unreachable!("we already handled uninhabited types"),
abi::Variants::Single { .. } => {
// The tag of a `Single` enum is like the tag of the niched
// variant: there's no tag as the discriminant is encoded

5
compiler/rustc_const_eval/src/interpret/validity.rs
View file

@ -302,7 +302,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
};
}
}
Variants::Single { .. } => {}
Variants::Single { .. } | Variants::Empty => {}
}
// Now we know we are projecting to a field, so figure out which one.
@ -344,6 +344,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
// Inside a variant
PathElem::Field(def.variant(index).fields[FieldIdx::from_usize(field)].name)
}
Variants::Empty => panic!("there is no field in Variants::Empty types"),
Variants::Multiple { .. } => bug!("we handled variants above"),
}
}
@ -1010,7 +1011,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
}
// Don't forget potential other variants.
match &layout.variants {
Variants::Single { .. } => {
Variants::Single { .. } | Variants::Empty => {
// Fully handled above.
}
Variants::Multiple { variants, .. } => {

4
compiler/rustc_const_eval/src/interpret/visitor.rs
View file

@ -218,8 +218,8 @@ pub trait ValueVisitor<'tcx, M: Machine<'tcx>>: Sized {
// recurse with the inner type
self.visit_variant(v, idx, &inner)?;
}
// For single-variant layouts, we already did anything there is to do.
Variants::Single { .. } => {}
// For single-variant layouts, we already did everything there is to do.
Variants::Single { .. } | Variants::Empty => {}
}
interp_ok(())

1
compiler/rustc_const_eval/src/util/check_validity_requirement.rs
View file

@ -155,6 +155,7 @@ fn check_validity_requirement_lax<'tcx>(
}
match &this.variants {
Variants::Empty => return Ok(false),
Variants::Single { .. } => {
// All fields of this single variant have already been checked above, there is nothing
// else to do.

2
compiler/rustc_middle/src/mir/interpret/error.rs
View file

@ -392,7 +392,7 @@ pub enum UndefinedBehaviorInfo<'tcx> {
/// A discriminant of an uninhabited enum variant is written.
UninhabitedEnumVariantWritten(VariantIdx),
/// An uninhabited enum variant is projected.
UninhabitedEnumVariantRead(VariantIdx),
UninhabitedEnumVariantRead(Option<VariantIdx>),
/// Trying to set discriminant to the niched variant, but the value does not match.
InvalidNichedEnumVariantWritten { enum_ty: Ty<'tcx> },
/// ABI-incompatible argument types.

15
compiler/rustc_middle/src/ty/layout.rs
View file

@ -734,21 +734,22 @@ where
let layout = match this.variants {
Variants::Single { index }
// If all variants but one are uninhabited, the variant layout is the enum layout.
if index == variant_index &&
// Don't confuse variants of uninhabited enums with the enum itself.
// For more details see https://github.com/rust-lang/rust/issues/69763.
this.fields != FieldsShape::Primitive =>
if index == variant_index =>
{
this.layout
}
Variants::Single { index } => {
Variants::Single { .. } | Variants::Empty => {
// Single-variant and no-variant enums *can* have other variants, but those are
// uninhabited. Produce a layout that has the right fields for that variant, so that
// the rest of the compiler can project fields etc as usual.
let tcx = cx.tcx();
let typing_env = cx.typing_env();
// Deny calling for_variant more than once for non-Single enums.
if let Ok(original_layout) = tcx.layout_of(typing_env.as_query_input(this.ty)) {
assert_eq!(original_layout.variants, Variants::Single { index });
assert_eq!(original_layout.variants, this.variants);
}
let fields = match this.ty.kind() {
@ -902,6 +903,7 @@ where
),
ty::Coroutine(def_id, args) => match this.variants {
Variants::Empty => unreachable!(),
Variants::Single { index } => TyMaybeWithLayout::Ty(
args.as_coroutine()
.state_tys(def_id, tcx)
@ -927,6 +929,7 @@ where
let field = &def.variant(index).fields[FieldIdx::from_usize(i)];
TyMaybeWithLayout::Ty(field.ty(tcx, args))
}
Variants::Empty => panic!("there is no field in Variants::Empty types"),
// Discriminant field for enums (where applicable).
Variants::Multiple { tag, .. } => {

31
compiler/rustc_mir_transform/src/jump_threading.rs
View file

@ -35,7 +35,6 @@
//! Likewise, applying the optimisation can create a lot of new MIR, so we bound the instruction
//! cost by `MAX_COST`.
use rustc_abi::{TagEncoding, Variants};
use rustc_arena::DroplessArena;
use rustc_const_eval::const_eval::DummyMachine;
use rustc_const_eval::interpret::{ImmTy, Immediate, InterpCx, OpTy, Projectable};
@ -565,31 +564,15 @@ impl<'a, 'tcx> TOFinder<'a, 'tcx> {
StatementKind::SetDiscriminant { box place, variant_index } => {
let Some(discr_target) = self.map.find_discr(place.as_ref()) else { return };
let enum_ty = place.ty(self.body, self.tcx).ty;
// `SetDiscriminant` may be a no-op if the assigned variant is the untagged variant
// of a niche encoding. If we cannot ensure that we write to the discriminant, do
// nothing.
let Ok(enum_layout) = self.ecx.layout_of(enum_ty) else {
// `SetDiscriminant` guarantees that the discriminant is now `variant_index`.
// Even if the discriminant write does nothing due to niches, it is UB to set the
// discriminant when the data does not encode the desired discriminant.
let Some(discr) =
self.ecx.discriminant_for_variant(enum_ty, *variant_index).discard_err()
else {
return;
};
let writes_discriminant = match enum_layout.variants {
Variants::Single { index } => {
assert_eq!(index, *variant_index);
true
}
Variants::Multiple { tag_encoding: TagEncoding::Direct, .. } => true,
Variants::Multiple {
tag_encoding: TagEncoding::Niche { untagged_variant, .. },
..
} => *variant_index != untagged_variant,
};
if writes_discriminant {
let Some(discr) =
self.ecx.discriminant_for_variant(enum_ty, *variant_index).discard_err()
else {
return;
};
self.process_immediate(bb, discr_target, discr, state);
}
self.process_immediate(bb, discr_target, discr, state);
}
// If we expect `lhs ?= true`, we have an opportunity if we assume `lhs == true`.
StatementKind::Intrinsic(box NonDivergingIntrinsic::Assume(

2
compiler/rustc_mir_transform/src/large_enums.rs
View file

@ -216,7 +216,7 @@ impl EnumSizeOpt {
};
let layout = tcx.layout_of(typing_env.as_query_input(ty)).ok()?;
let variants = match &layout.variants {
Variants::Single { .. } => return None,
Variants::Single { .. } | Variants::Empty => return None,
Variants::Multiple { tag_encoding: TagEncoding::Niche { .. }, .. } => return None,
Variants::Multiple { variants, .. } if variants.len() <= 1 => return None,

4
compiler/rustc_mir_transform/src/unreachable_enum_branching.rs
View file

@ -54,6 +54,10 @@ fn variant_discriminants<'tcx>(
tcx: TyCtxt<'tcx>,
) -> FxHashSet<u128> {
match &layout.variants {
Variants::Empty => {
// Uninhabited, no valid discriminant.
FxHashSet::default()
}
Variants::Single { index } => {
let mut res = FxHashSet::default();
res.insert(

1
compiler/rustc_smir/src/rustc_smir/convert/abi.rs
View file

@ -167,6 +167,7 @@ impl<'tcx> Stable<'tcx> for rustc_abi::Variants<rustc_abi::FieldIdx, rustc_abi::
rustc_abi::Variants::Single { index } => {
VariantsShape::Single { index: index.stable(tables) }
}
rustc_abi::Variants::Empty => VariantsShape::Empty,
rustc_abi::Variants::Multiple { tag, tag_encoding, tag_field, variants } => {
VariantsShape::Multiple {
tag: tag.stable(tables),

2
compiler/rustc_target/src/callconv/loongarch.rs
View file

@ -116,7 +116,7 @@ where
FieldsShape::Arbitrary { .. } => {
match arg_layout.variants {
abi::Variants::Multiple { .. } => return Err(CannotUseFpConv),
abi::Variants::Single { .. } => (),
abi::Variants::Single { .. } | abi::Variants::Empty => (),
}
for i in arg_layout.fields.index_by_increasing_offset() {
let field = arg_layout.field(cx, i);

2
compiler/rustc_target/src/callconv/riscv.rs
View file

@ -122,7 +122,7 @@ where
FieldsShape::Arbitrary { .. } => {
match arg_layout.variants {
abi::Variants::Multiple { .. } => return Err(CannotUseFpConv),
abi::Variants::Single { .. } => (),
abi::Variants::Single { .. } | abi::Variants::Empty => (),
}
for i in arg_layout.fields.index_by_increasing_offset() {
let field = arg_layout.field(cx, i);

2
compiler/rustc_target/src/callconv/x86_64.rs
View file

@ -65,7 +65,7 @@ where
}
match &layout.variants {
abi::Variants::Single { .. } => {}
abi::Variants::Single { .. } | abi::Variants::Empty => {}
abi::Variants::Multiple { variants, .. } => {
// Treat enum variants like union members.
for variant_idx in variants.indices() {

18
compiler/rustc_transmute/src/layout/tree.rs
View file

@ -338,16 +338,11 @@ pub(crate) mod rustc {
};
match layout.variants() {
Variants::Empty => Ok(Self::uninhabited()),
Variants::Single { index } => {
// 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::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
@ -500,6 +495,10 @@ pub(crate) mod rustc {
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
i: FieldIdx,
) -> Ty<'tcx> {
// We cannot use `ty_and_layout_field` to retrieve the field type, since
// `ty_and_layout_field` erases regions in the returned type. We must
// not erase regions here, since we may need to ultimately emit outlives
// obligations as a consequence of the transmutability analysis.
match ty.kind() {
ty::Adt(def, args) => {
match layout.variants {
@ -507,6 +506,7 @@ pub(crate) mod rustc {
let field = &def.variant(index).fields[i];
field.ty(cx.tcx(), args)
}
Variants::Empty => panic!("there is no field in Variants::Empty types"),
// Discriminant field for enums (where applicable).
Variants::Multiple { tag, .. } => {
assert_eq!(i.as_usize(), 0);

14
compiler/rustc_ty_utils/src/layout.rs
View file

@ -1104,15 +1104,13 @@ fn variant_info_for_adt<'tcx>(
};
match layout.variants {
Variants::Empty => (vec![], None),
Variants::Single { index } => {
if !adt_def.variants().is_empty() && layout.fields != FieldsShape::Primitive {
debug!("print-type-size `{:#?}` variant {}", layout, adt_def.variant(index).name);
let variant_def = &adt_def.variant(index);
let fields: Vec<_> = variant_def.fields.iter().map(|f| f.name).collect();
(vec![build_variant_info(Some(variant_def.name), &fields, layout)], None)
} else {
(vec![], None)
}
debug!("print-type-size `{:#?}` variant {}", layout, adt_def.variant(index).name);
let variant_def = &adt_def.variant(index);
let fields: Vec<_> = variant_def.fields.iter().map(|f| f.name).collect();
(vec![build_variant_info(Some(variant_def.name), &fields, layout)], None)
}
Variants::Multiple { tag, ref tag_encoding, .. } => {

124
compiler/rustc_ty_utils/src/layout/invariant.rs
View file

@ -241,63 +241,81 @@ pub(super) fn layout_sanity_check<'tcx>(cx: &LayoutCx<'tcx>, layout: &TyAndLayou
check_layout_abi(cx, layout);
if let Variants::Multiple { variants, tag, tag_encoding, .. } = &layout.variants {
if let TagEncoding::Niche { niche_start, untagged_variant, niche_variants } = tag_encoding {
let niche_size = tag.size(cx);
assert!(*niche_start <= niche_size.unsigned_int_max());
for (idx, variant) in variants.iter_enumerated() {
// Ensure all inhabited variants are accounted for.
if !variant.is_uninhabited() {
assert!(idx == *untagged_variant || niche_variants.contains(&idx));
}
match &layout.variants {
Variants::Empty => {
assert!(layout.is_uninhabited());
}
Variants::Single { index } => {
if let Some(variants) = layout.ty.variant_range(tcx) {
assert!(variants.contains(index));
} else {
// Types without variants use `0` as dummy variant index.
assert!(index.as_u32() == 0);
}
}
for variant in variants.iter() {
// No nested "multiple".
assert_matches!(variant.variants, Variants::Single { .. });
// Variants should have the same or a smaller size as the full thing,
// and same for alignment.
if variant.size > layout.size {
bug!(
"Type with size {} bytes has variant with size {} bytes: {layout:#?}",
layout.size.bytes(),
variant.size.bytes(),
)
}
if variant.align.abi > layout.align.abi {
bug!(
"Type with alignment {} bytes has variant with alignment {} bytes: {layout:#?}",
layout.align.abi.bytes(),
variant.align.abi.bytes(),
)
}
// Skip empty variants.
if variant.size == Size::ZERO || variant.fields.count() == 0 || variant.is_uninhabited()
Variants::Multiple { variants, tag, tag_encoding, .. } => {
if let TagEncoding::Niche { niche_start, untagged_variant, niche_variants } =
tag_encoding
{
// These are never actually accessed anyway, so we can skip the coherence check
// for them. They also fail that check, since they have
// `Aggregate`/`Uninhabited` ABI even when the main type is
// `Scalar`/`ScalarPair`. (Note that sometimes, variants with fields have size
// 0, and sometimes, variants without fields have non-0 size.)
continue;
}
// The top-level ABI and the ABI of the variants should be coherent.
let scalar_coherent =
|s1: Scalar, s2: Scalar| s1.size(cx) == s2.size(cx) && s1.align(cx) == s2.align(cx);
let abi_coherent = match (layout.backend_repr, variant.backend_repr) {
(BackendRepr::Scalar(s1), BackendRepr::Scalar(s2)) => scalar_coherent(s1, s2),
(BackendRepr::ScalarPair(a1, b1), BackendRepr::ScalarPair(a2, b2)) => {
scalar_coherent(a1, a2) && scalar_coherent(b1, b2)
let niche_size = tag.size(cx);
assert!(*niche_start <= niche_size.unsigned_int_max());
for (idx, variant) in variants.iter_enumerated() {
// Ensure all inhabited variants are accounted for.
if !variant.is_uninhabited() {
assert!(idx == *untagged_variant || niche_variants.contains(&idx));
}
}
}
for variant in variants.iter() {
// No nested "multiple".
assert_matches!(variant.variants, Variants::Single { .. });
// Variants should have the same or a smaller size as the full thing,
// and same for alignment.
if variant.size > layout.size {
bug!(
"Type with size {} bytes has variant with size {} bytes: {layout:#?}",
layout.size.bytes(),
variant.size.bytes(),
)
}
if variant.align.abi > layout.align.abi {
bug!(
"Type with alignment {} bytes has variant with alignment {} bytes: {layout:#?}",
layout.align.abi.bytes(),
variant.align.abi.bytes(),
)
}
// Skip empty variants.
if variant.size == Size::ZERO
|| variant.fields.count() == 0
|| variant.is_uninhabited()
{
// These are never actually accessed anyway, so we can skip the coherence check
// for them. They also fail that check, since they have
// `Aggregate`/`Uninhabited` ABI even when the main type is
// `Scalar`/`ScalarPair`. (Note that sometimes, variants with fields have size
// 0, and sometimes, variants without fields have non-0 size.)
continue;
}
// The top-level ABI and the ABI of the variants should be coherent.
let scalar_coherent = |s1: Scalar, s2: Scalar| {
s1.size(cx) == s2.size(cx) && s1.align(cx) == s2.align(cx)
};
let abi_coherent = match (layout.backend_repr, variant.backend_repr) {
(BackendRepr::Scalar(s1), BackendRepr::Scalar(s2)) => scalar_coherent(s1, s2),
(BackendRepr::ScalarPair(a1, b1), BackendRepr::ScalarPair(a2, b2)) => {
scalar_coherent(a1, a2) && scalar_coherent(b1, b2)
}
(BackendRepr::Uninhabited, _) => true,
(BackendRepr::Memory { .. }, _) => true,
_ => false,
};
if !abi_coherent {
bug!(
"Variant ABI is incompatible with top-level ABI:\nvariant={:#?}\nTop-level: {layout:#?}",
variant
);
}
(BackendRepr::Uninhabited, _) => true,
(BackendRepr::Memory { .. }, _) => true,
_ => false,
};
if !abi_coherent {
bug!(
"Variant ABI is incompatible with top-level ABI:\nvariant={:#?}\nTop-level: {layout:#?}",
variant
);
}
}
}

3
compiler/stable_mir/src/abi.rs
View file

@ -180,6 +180,9 @@ impl FieldsShape {
#[derive(Clone, Debug, PartialEq, Eq, Hash, Serialize)]
pub enum VariantsShape {
/// A type with no valid variants. Must be uninhabited.
Empty,
/// Single enum variants, structs/tuples, unions, and all non-ADTs.
Single { index: VariantIdx },

2
src/tools/miri/src/helpers.rs
View file

@ -605,7 +605,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
// `UnsafeCell` action.
(self.unsafe_cell_action)(v)
}
Variants::Single { .. } => {
Variants::Single { .. } | Variants::Empty => {
// Proceed further, try to find where exactly that `UnsafeCell`
// is hiding.
self.walk_value(v)

5
src/tools/rust-analyzer/crates/hir-ty/src/mir/eval.rs
View file

@ -813,7 +813,7 @@ impl Evaluator<'_> {
ProjectionElem::Field(Either::Left(f)) => {
let layout = self.layout(&prev_ty)?;
let variant_layout = match &layout.variants {
Variants::Single { .. } => &layout,
Variants::Single { .. } | Variants::Empty => &layout,
Variants::Multiple { variants, .. } => {
&variants[match f.parent {
hir_def::VariantId::EnumVariantId(it) => {
@ -1638,6 +1638,7 @@ impl Evaluator<'_> {
return Ok(0);
};
match &layout.variants {
Variants::Empty => unreachable!(),
Variants::Single { index } => {
let r = self.const_eval_discriminant(self.db.enum_data(e).variants[index.0].0)?;
Ok(r)
@ -1800,7 +1801,7 @@ impl Evaluator<'_> {
}
let layout = self.layout_adt(adt, subst)?;
Ok(match &layout.variants {
Variants::Single { .. } => (layout.size.bytes_usize(), layout, None),
Variants::Single { .. } | Variants::Empty => (layout.size.bytes_usize(), layout, None),
Variants::Multiple { variants, tag, tag_encoding, .. } => {
let enum_variant_id = match it {
VariantId::EnumVariantId(it) => it,

1
src/tools/rust-analyzer/crates/hir-ty/src/utils.rs
View file

@ -334,6 +334,7 @@ pub(crate) fn detect_variant_from_bytes<'a>(
e: EnumId,
) -> Option<(EnumVariantId, &'a Layout)> {
let (var_id, var_layout) = match &layout.variants {
hir_def::layout::Variants::Empty => unreachable!(),
hir_def::layout::Variants::Single { index } => {
(db.enum_data(e).variants[index.0].0, layout)
}

3
tests/mir-opt/set_no_discriminant.f.JumpThreading.diff
View file

@ -10,7 +10,8 @@
_2 = E::<char>::A;
discriminant(_2) = 1;
_1 = discriminant(_2);
switchInt(copy _1) -> [0: bb1, otherwise: bb2];
- switchInt(copy _1) -> [0: bb1, otherwise: bb2];
+ goto -> bb2;
}
bb1: {

3
tests/mir-opt/set_no_discriminant.generic.JumpThreading.diff
View file

@ -10,7 +10,8 @@
_2 = E::<T>::A;
discriminant(_2) = 1;
_1 = discriminant(_2);
switchInt(copy _1) -> [0: bb1, otherwise: bb2];
- switchInt(copy _1) -> [0: bb1, otherwise: bb2];
+ goto -> bb2;
}
bb1: {

21
tests/mir-opt/set_no_discriminant.rs
View file

@ -1,5 +1,6 @@
// `SetDiscriminant` does not actually write anything if the chosen variant is the untagged variant
// of a niche encoding. Verify that we do not thread over this case.
// of a niche encoding. However, it is UB to call `SetDiscriminant` with the untagged variant if the
// value currently encodes a different variant. Verify that we do correctly thread in this case.
//@ test-mir-pass: JumpThreading
#![feature(custom_mir)]
@ -16,20 +17,21 @@ enum E<T> {
#[custom_mir(dialect = "runtime")]
pub fn f() -> usize {
// CHECK-LABEL: fn f(
// CHECK-NOT: goto
// CHECK: switchInt(
// CHECK-NOT: goto
// CHECK-NOT: switchInt
// CHECK: goto
// CHECK-NOT: switchInt
mir! {
let a: isize;
let e: E<char>;
{
e = E::A;
SetDiscriminant(e, 1);
SetDiscriminant(e, 1); // UB!
a = Discriminant(e);
match a {
0 => bb0,
_ => bb1,
}
}
bb0 = {
RET = 0;
@ -46,15 +48,15 @@ pub fn f() -> usize {
#[custom_mir(dialect = "runtime")]
pub fn generic<T>() -> usize {
// CHECK-LABEL: fn generic(
// CHECK-NOT: goto
// CHECK: switchInt(
// CHECK-NOT: goto
// CHECK-NOT: switchInt
// CHECK: goto
// CHECK-NOT: switchInt
mir! {
let a: isize;
let e: E<T>;
{
e = E::A;
SetDiscriminant(e, 1);
SetDiscriminant(e, 1); // UB!
a = Discriminant(e);
match a {
0 => bb0,
@ -72,6 +74,7 @@ pub fn generic<T>() -> usize {
}
}
// CHECK-LABEL: fn main(
fn main() {
assert_eq!(f(), 0);
assert_eq!(generic::<char>(), 0);