Rollup merge of rust-lang#132255 - workingjubilee:layout-is-🏚️, r=compiler-errors

matthiaskrgr · web-flow · commit baa72e60e1c7 · 2024-10-29T06:34:29.000+01:00
Add `LayoutData::is_uninhabited` and use it

Use accessors for the things that accessors are good at: reducing everyone's need to be nosy and peek at the internals of every data structure.
diff --git a/Cargo.lock b/Cargo.lock
@@ -4100,6 +4100,7 @@ version = "0.0.0"
 dependencies = [
  "either",
  "itertools",
+ "rustc_abi",
  "rustc_arena",
  "rustc_ast",
  "rustc_attr",
diff --git a/compiler/rustc_abi/src/layout.rs b/compiler/rustc_abi/src/layout.rs
@@ -28,7 +28,7 @@ where
     VariantIdx: Idx,
     F: Deref<Target = &'a LayoutData<FieldIdx, VariantIdx>> + fmt::Debug,
 {
-    let uninhabited = fields.iter().any(|f| f.abi.is_uninhabited());
+    let uninhabited = fields.iter().any(|f| f.is_uninhabited());
     // We cannot ignore alignment; that might lead us to entirely discard a variant and
     // produce an enum that is less aligned than it should be!
     let is_1zst = fields.iter().all(|f| f.is_1zst());
@@ -681,7 +681,7 @@ impl<Cx: HasDataLayout> LayoutCalculator<Cx> {
         let discr_type = repr.discr_type();
         let bits = Integer::from_attr(dl, discr_type).size().bits();
         for (i, mut val) in discriminants {
-            if !repr.c() && variants[i].iter().any(|f| f.abi.is_uninhabited()) {
+            if !repr.c() && variants[i].iter().any(|f| f.is_uninhabited()) {
                 continue;
             }
             if discr_type.is_signed() {
diff --git a/compiler/rustc_abi/src/lib.rs b/compiler/rustc_abi/src/lib.rs
@@ -1652,6 +1652,11 @@ impl<FieldIdx: Idx, VariantIdx: Idx> LayoutData<FieldIdx, VariantIdx> {
         }
     }
 
+    /// Returns `true` if this is an uninhabited type
+    pub fn is_uninhabited(&self) -> bool {
+        self.abi.is_uninhabited()
+    }
+
     pub fn scalar<C: HasDataLayout>(cx: &C, scalar: Scalar) -> Self {
         let largest_niche = Niche::from_scalar(cx, Size::ZERO, scalar);
         let size = scalar.size(cx);
diff --git a/compiler/rustc_codegen_llvm/src/abi.rs b/compiler/rustc_codegen_llvm/src/abi.rs
@@ -415,7 +415,7 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
         instance: Option<ty::Instance<'tcx>>,
     ) {
         let mut func_attrs = SmallVec::<[_; 3]>::new();
-        if self.ret.layout.abi.is_uninhabited() {
+        if self.ret.layout.is_uninhabited() {
             func_attrs.push(llvm::AttributeKind::NoReturn.create_attr(cx.llcx));
         }
         if !self.can_unwind {
@@ -532,7 +532,7 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
 
     fn apply_attrs_callsite(&self, bx: &mut Builder<'_, 'll, 'tcx>, callsite: &'ll Value) {
         let mut func_attrs = SmallVec::<[_; 2]>::new();
-        if self.ret.layout.abi.is_uninhabited() {
+        if self.ret.layout.is_uninhabited() {
             func_attrs.push(llvm::AttributeKind::NoReturn.create_attr(bx.cx.llcx));
         }
         if !self.can_unwind {
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs b/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs
@@ -364,7 +364,7 @@ impl<'ll, 'tcx> DebugInfoCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
 
         let mut flags = DIFlags::FlagPrototyped;
 
-        if fn_abi.ret.layout.abi.is_uninhabited() {
+        if fn_abi.ret.layout.is_uninhabited() {
             flags |= DIFlags::FlagNoReturn;
         }
 
diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -438,7 +438,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 _ => bug!("C-variadic function must have a `VaList` place"),
             }
         }
-        if self.fn_abi.ret.layout.abi.is_uninhabited() {
+        if self.fn_abi.ret.layout.is_uninhabited() {
             // Functions with uninhabited return values are marked `noreturn`,
             // so we should make sure that we never actually do.
             // We play it safe by using a well-defined `abort`, but we could go for immediate UB
@@ -774,7 +774,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             Some(if do_panic {
                 let msg_str = with_no_visible_paths!({
                     with_no_trimmed_paths!({
-                        if layout.abi.is_uninhabited() {
+                        if layout.is_uninhabited() {
                             // Use this error even for the other intrinsics as it is more precise.
                             format!("attempted to instantiate uninhabited type `{ty}`")
                         } else if requirement == ValidityRequirement::Zero {
diff --git a/compiler/rustc_codegen_ssa/src/mir/place.rs b/compiler/rustc_codegen_ssa/src/mir/place.rs
@@ -55,7 +55,7 @@ impl<V: CodegenObject> PlaceValue<V> {
     /// Creates a `PlaceRef` to this location with the given type.
     pub fn with_type<'tcx>(self, layout: TyAndLayout<'tcx>) -> PlaceRef<'tcx, V> {
         assert!(
-            layout.is_unsized() || layout.abi.is_uninhabited() || self.llextra.is_none(),
+            layout.is_unsized() || layout.is_uninhabited() || self.llextra.is_none(),
             "Had pointer metadata {:?} for sized type {layout:?}",
             self.llextra,
         );
@@ -239,7 +239,7 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
         let dl = &bx.tcx().data_layout;
         let cast_to_layout = bx.cx().layout_of(cast_to);
         let cast_to = bx.cx().immediate_backend_type(cast_to_layout);
-        if self.layout.abi.is_uninhabited() {
+        if self.layout.is_uninhabited() {
             return bx.cx().const_poison(cast_to);
         }
         let (tag_scalar, tag_encoding, tag_field) = match self.layout.variants {
@@ -358,7 +358,7 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
         bx: &mut Bx,
         variant_index: VariantIdx,
     ) {
-        if self.layout.for_variant(bx.cx(), variant_index).abi.is_uninhabited() {
+        if self.layout.for_variant(bx.cx(), variant_index).is_uninhabited() {
             // We play it safe by using a well-defined `abort`, but we could go for immediate UB
             // if that turns out to be helpful.
             bx.abort();
diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
@@ -203,10 +203,10 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
     ) -> Option<OperandValue<Bx::Value>> {
         // Check for transmutes that are always UB.
         if operand.layout.size != cast.size
-            || operand.layout.abi.is_uninhabited()
-            || cast.abi.is_uninhabited()
+            || operand.layout.is_uninhabited()
+            || cast.is_uninhabited()
         {
-            if !operand.layout.abi.is_uninhabited() {
+            if !operand.layout.is_uninhabited() {
                 // Since this is known statically and the input could have existed
                 // without already having hit UB, might as well trap for it.
                 bx.abort();
@@ -555,7 +555,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
                         assert!(bx.cx().is_backend_immediate(cast));
                         let to_backend_ty = bx.cx().immediate_backend_type(cast);
-                        if operand.layout.abi.is_uninhabited() {
+                        if operand.layout.is_uninhabited() {
                             let val = OperandValue::Immediate(bx.cx().const_poison(to_backend_ty));
                             return OperandRef { val, layout: cast };
                         }
diff --git a/compiler/rustc_const_eval/src/const_eval/machine.rs b/compiler/rustc_const_eval/src/const_eval/machine.rs
@@ -395,7 +395,7 @@ impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {
 
     #[inline(always)]
     fn enforce_validity(ecx: &InterpCx<'tcx, Self>, layout: TyAndLayout<'tcx>) -> bool {
-        ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks || layout.abi.is_uninhabited()
+        ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks || layout.is_uninhabited()
     }
 
     fn load_mir(
diff --git a/compiler/rustc_const_eval/src/interpret/discriminant.rs b/compiler/rustc_const_eval/src/interpret/discriminant.rs
@@ -27,7 +27,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         // discriminant, so we cannot do anything here.
         // When evaluating we will always error before even getting here, but ConstProp 'executes'
         // dead code, so we cannot ICE here.
-        if dest.layout().for_variant(self, variant_index).abi.is_uninhabited() {
+        if dest.layout().for_variant(self, variant_index).is_uninhabited() {
             throw_ub!(UninhabitedEnumVariantWritten(variant_index))
         }
 
@@ -86,7 +86,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                     // 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).abi.is_uninhabited() {
+                    if op.layout().for_variant(self, index).is_uninhabited() {
                         throw_ub!(UninhabitedEnumVariantRead(index))
                     }
                 }
@@ -203,7 +203,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         // Reading the discriminant of an uninhabited variant is UB. This is the basis for the
         // `uninhabited_enum_branching` MIR pass. It also ensures consistency with
         // `write_discriminant`.
-        if op.layout().for_variant(self, index).abi.is_uninhabited() {
+        if op.layout().for_variant(self, index).is_uninhabited() {
             throw_ub!(UninhabitedEnumVariantRead(index))
         }
         interp_ok(index)
diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics.rs b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
@@ -364,7 +364,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                     let msg = match requirement {
                         // For *all* intrinsics we first check `is_uninhabited` to give a more specific
                         // error message.
-                        _ if layout.abi.is_uninhabited() => format!(
+                        _ if layout.is_uninhabited() => format!(
                             "aborted execution: attempted to instantiate uninhabited type `{ty}`"
                         ),
                         ValidityRequirement::Inhabited => bug!("handled earlier"),
diff --git a/compiler/rustc_const_eval/src/interpret/operator.rs b/compiler/rustc_const_eval/src/interpret/operator.rs
@@ -315,7 +315,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 let ptr = left.to_scalar().to_pointer(self)?;
                 let pointee_ty = left.layout.ty.builtin_deref(true).unwrap();
                 let pointee_layout = self.layout_of(pointee_ty)?;
-                assert!(pointee_layout.abi.is_sized());
+                assert!(pointee_layout.is_sized());
 
                 // The size always fits in `i64` as it can be at most `isize::MAX`.
                 let pointee_size = i64::try_from(pointee_layout.size.bytes()).unwrap();
@@ -518,14 +518,14 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
 
         interp_ok(match null_op {
             SizeOf => {
-                if !layout.abi.is_sized() {
+                if !layout.is_sized() {
                     span_bug!(self.cur_span(), "unsized type for `NullaryOp::SizeOf`");
                 }
                 let val = layout.size.bytes();
                 ImmTy::from_uint(val, usize_layout())
             }
             AlignOf => {
-                if !layout.abi.is_sized() {
+                if !layout.is_sized() {
                     span_bug!(self.cur_span(), "unsized type for `NullaryOp::AlignOf`");
                 }
                 let val = layout.align.abi.bytes();
diff --git a/compiler/rustc_const_eval/src/interpret/validity.rs b/compiler/rustc_const_eval/src/interpret/validity.rs
@@ -542,7 +542,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
             throw_validation_failure!(self.path, NullPtr { ptr_kind })
         }
         // Do not allow references to uninhabited types.
-        if place.layout.abi.is_uninhabited() {
+        if place.layout.is_uninhabited() {
             let ty = place.layout.ty;
             throw_validation_failure!(self.path, PtrToUninhabited { ptr_kind, ty })
         }
@@ -867,7 +867,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
     /// Add the entire given place to the "data" range of this visit.
     fn add_data_range_place(&mut self, place: &PlaceTy<'tcx, M::Provenance>) {
         // Only sized places can be added this way.
-        debug_assert!(place.layout.abi.is_sized());
+        debug_assert!(place.layout.is_sized());
         if let Some(data_bytes) = self.data_bytes.as_mut() {
             let offset = Self::data_range_offset(self.ecx, place);
             data_bytes.add_range(offset, place.layout.size);
@@ -945,7 +945,7 @@ impl<'rt, 'tcx, M: Machine<'tcx>> ValidityVisitor<'rt, 'tcx, M> {
         layout: TyAndLayout<'tcx>,
     ) -> Cow<'e, RangeSet> {
         assert!(layout.ty.is_union());
-        assert!(layout.abi.is_sized(), "there are no unsized unions");
+        assert!(layout.is_sized(), "there are no unsized unions");
         let layout_cx = LayoutCx::new(*ecx.tcx, ecx.param_env);
         return M::cached_union_data_range(ecx, layout.ty, || {
             let mut out = RangeSet(Vec::new());
diff --git a/compiler/rustc_const_eval/src/util/check_validity_requirement.rs b/compiler/rustc_const_eval/src/util/check_validity_requirement.rs
@@ -29,7 +29,7 @@ pub fn check_validity_requirement<'tcx>(
 
     // There is nothing strict or lax about inhabitedness.
     if kind == ValidityRequirement::Inhabited {
-        return Ok(!layout.abi.is_uninhabited());
+        return Ok(!layout.is_uninhabited());
     }
 
     let layout_cx = LayoutCx::new(tcx, param_env_and_ty.param_env);
diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs
@@ -172,7 +172,7 @@ fn check_static_inhabited(tcx: TyCtxt<'_>, def_id: LocalDefId) {
             return;
         }
     };
-    if layout.abi.is_uninhabited() {
+    if layout.is_uninhabited() {
         tcx.node_span_lint(
             UNINHABITED_STATIC,
             tcx.local_def_id_to_hir_id(def_id),
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
@@ -346,7 +346,7 @@ impl<'tcx> SizeSkeleton<'tcx> {
         // First try computing a static layout.
         let err = match tcx.layout_of(param_env.and(ty)) {
             Ok(layout) => {
-                if layout.abi.is_sized() {
+                if layout.is_sized() {
                     return Ok(SizeSkeleton::Known(layout.size, Some(layout.align.abi)));
                 } else {
                     // Just to be safe, don't claim a known layout for unsized types.
diff --git a/compiler/rustc_mir_transform/Cargo.toml b/compiler/rustc_mir_transform/Cargo.toml
@@ -7,6 +7,7 @@ edition = "2021"
 # tidy-alphabetical-start
 either = "1"
 itertools = "0.12"
+rustc_abi = { path = "../rustc_abi" }
 rustc_arena = { path = "../rustc_arena" }
 rustc_ast = { path = "../rustc_ast" }
 rustc_attr = { path = "../rustc_attr" }
diff --git a/compiler/rustc_mir_transform/src/unreachable_enum_branching.rs b/compiler/rustc_mir_transform/src/unreachable_enum_branching.rs
@@ -1,5 +1,6 @@
 //! A pass that eliminates branches on uninhabited or unreachable enum variants.
 
+use rustc_abi::Variants;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_middle::bug;
 use rustc_middle::mir::patch::MirPatch;
@@ -9,7 +10,6 @@ use rustc_middle::mir::{
 };
 use rustc_middle::ty::layout::TyAndLayout;
 use rustc_middle::ty::{Ty, TyCtxt};
-use rustc_target::abi::{Abi, Variants};
 use tracing::trace;
 
 pub(super) struct UnreachableEnumBranching;
@@ -65,7 +65,7 @@ fn variant_discriminants<'tcx>(
         Variants::Multiple { variants, .. } => variants
             .iter_enumerated()
             .filter_map(|(idx, layout)| {
-                (layout.abi != Abi::Uninhabited)
+                (!layout.is_uninhabited())
                     .then(|| ty.discriminant_for_variant(tcx, idx).unwrap().val)
             })
             .collect(),
diff --git a/compiler/rustc_transmute/src/layout/tree.rs b/compiler/rustc_transmute/src/layout/tree.rs
@@ -339,9 +339,7 @@ pub(crate) mod rustc {
             // 2. enums that delegate their layout to a variant
             // 3. enums with multiple variants
             match layout.variants() {
-                Variants::Single { .. }
-                    if layout.abi.is_uninhabited() && layout.size == Size::ZERO =>
-                {
+                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
diff --git a/compiler/rustc_ty_utils/src/layout/invariant.rs b/compiler/rustc_ty_utils/src/layout/invariant.rs
@@ -10,7 +10,7 @@ pub(super) fn partially_check_layout<'tcx>(cx: &LayoutCx<'tcx>, layout: &TyAndLa
 
     // Type-level uninhabitedness should always imply ABI uninhabitedness.
     if layout.ty.is_privately_uninhabited(tcx, cx.param_env) {
-        assert!(layout.abi.is_uninhabited());
+        assert!(layout.is_uninhabited());
     }
 
     if layout.size.bytes() % layout.align.abi.bytes() != 0 {
@@ -262,9 +262,7 @@ pub(super) fn partially_check_layout<'tcx>(cx: &LayoutCx<'tcx>, layout: &TyAndLa
                 )
             }
             // Skip empty variants.
-            if variant.size == Size::ZERO
-                || variant.fields.count() == 0
-                || variant.abi.is_uninhabited()
+            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
diff --git a/src/librustdoc/html/render/type_layout.rs b/src/librustdoc/html/render/type_layout.rs
@@ -60,8 +60,8 @@ pub(crate) fn document_type_layout<'a, 'cx: 'a>(
                         span_bug!(tcx.def_span(ty_def_id), "not an adt")
                     };
                     let name = adt.variant(variant_idx).name;
-                    let is_unsized = variant_layout.abi.is_unsized();
-                    let is_uninhabited = variant_layout.abi.is_uninhabited();
+                    let is_unsized = variant_layout.is_unsized();
+                    let is_uninhabited = variant_layout.is_uninhabited();
                     let size = variant_layout.size.bytes() - tag_size;
                     let type_layout_size = TypeLayoutSize { is_unsized, is_uninhabited, size };
                     (name, type_layout_size)
@@ -72,8 +72,8 @@ pub(crate) fn document_type_layout<'a, 'cx: 'a>(
         };
 
         let type_layout_size = tcx.layout_of(param_env.and(ty)).map(|layout| {
-            let is_unsized = layout.abi.is_unsized();
-            let is_uninhabited = layout.abi.is_uninhabited();
+            let is_unsized = layout.is_unsized();
+            let is_uninhabited = layout.is_uninhabited();
             let size = layout.size.bytes();
             TypeLayoutSize { is_unsized, is_uninhabited, size }
         });

Original file line number	Diff line number	Diff line change
`@@ -1652,6 +1652,11 @@ impl<FieldIdx: Idx, VariantIdx: Idx> LayoutData<FieldIdx, VariantIdx> {`
`1652`	`1652`	`}`
`1653`	`1653`	`}`
`1654`	`1654`
	`1655`	+ /// Returns `true` if this is an uninhabited type
	`1656`	`+ pub fn is_uninhabited(&self) -> bool {`
	`1657`	`+ self.abi.is_uninhabited()`
	`1658`	`+ }`
	`1659`	`+`
`1655`	`1660`	`pub fn scalar<C: HasDataLayout>(cx: &C, scalar: Scalar) -> Self {`
`1656`	`1661`	`let largest_niche = Niche::from_scalar(cx, Size::ZERO, scalar);`
`1657`	`1662`	`let size = scalar.size(cx);`
Original file line number	Diff line number	Diff line change
`@@ -364,7 +364,7 @@ impl<'ll, 'tcx> DebugInfoCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {`
`364`	`364`
`365`	`365`	`let mut flags = DIFlags::FlagPrototyped;`
`366`	`366`
`367`		`- if fn_abi.ret.layout.abi.is_uninhabited() {`
	`367`	`+ if fn_abi.ret.layout.is_uninhabited() {`
`368`	`368`	`flags \|= DIFlags::FlagNoReturn;`
`369`	`369`	`}`
`370`	`370`
Original file line number	Diff line number	Diff line change
`@@ -395,7 +395,7 @@ impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {`
`395`	`395`
`396`	`396`	`#[inline(always)]`
`397`	`397`	`fn enforce_validity(ecx: &InterpCx<'tcx, Self>, layout: TyAndLayout<'tcx>) -> bool {`
`398`		`- ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks \|\| layout.abi.is_uninhabited()`
	`398`	`+ ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks \|\| layout.is_uninhabited()`
`399`	`399`	`}`
`400`	`400`
`401`	`401`	`fn load_mir(`
Original file line number	Diff line number	Diff line change
`@@ -27,7 +27,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {`
`27`	`27`	`// discriminant, so we cannot do anything here.`
`28`	`28`	`// When evaluating we will always error before even getting here, but ConstProp 'executes'`
`29`	`29`	`// dead code, so we cannot ICE here.`
`30`		`- if dest.layout().for_variant(self, variant_index).abi.is_uninhabited() {`
	`30`	`+ if dest.layout().for_variant(self, variant_index).is_uninhabited() {`
`31`	`31`	`throw_ub!(UninhabitedEnumVariantWritten(variant_index))`
`32`	`32`	`}`
`33`	`33`
`@@ -86,7 +86,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {`
`86`	`86`	// For consistency with `write_discriminant`, and to make sure that
`87`	`87`	// `project_downcast` cannot fail due to strange layouts, we declare immediate UB
`88`	`88`	`// for uninhabited variants.`
`89`		`- if op.layout().for_variant(self, index).abi.is_uninhabited() {`
	`89`	`+ if op.layout().for_variant(self, index).is_uninhabited() {`
`90`	`90`	`throw_ub!(UninhabitedEnumVariantRead(index))`
`91`	`91`	`}`
`92`	`92`	`}`
`@@ -203,7 +203,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {`
`203`	`203`	`// Reading the discriminant of an uninhabited variant is UB. This is the basis for the`
`204`	`204`	// `uninhabited_enum_branching` MIR pass. It also ensures consistency with
`205`	`205`	// `write_discriminant`.
`206`		`- if op.layout().for_variant(self, index).abi.is_uninhabited() {`
	`206`	`+ if op.layout().for_variant(self, index).is_uninhabited() {`
`207`	`207`	`throw_ub!(UninhabitedEnumVariantRead(index))`
`208`	`208`	`}`
`209`	`209`	`interp_ok(index)`