diff options
Diffstat (limited to 'compiler/rustc_const_eval/src/interpret/visitor.rs')
| -rw-r--r-- | compiler/rustc_const_eval/src/interpret/visitor.rs | 694 |
1 files changed, 177 insertions, 517 deletions
diff --git a/compiler/rustc_const_eval/src/interpret/visitor.rs b/compiler/rustc_const_eval/src/interpret/visitor.rs index 8d7c1953abe..a50233fa3de 100644 --- a/compiler/rustc_const_eval/src/interpret/visitor.rs +++ b/compiler/rustc_const_eval/src/interpret/visitor.rs @@ -1,544 +1,204 @@ //! Visitor for a run-time value with a given layout: Traverse enums, structs and other compound //! types until we arrive at the leaves, with custom handling for primitive types. +use rustc_index::IndexVec; use rustc_middle::mir::interpret::InterpResult; use rustc_middle::ty; -use rustc_middle::ty::layout::TyAndLayout; +use rustc_target::abi::FieldIdx; use rustc_target::abi::{FieldsShape, VariantIdx, Variants}; use std::num::NonZeroUsize; -use super::{InterpCx, MPlaceTy, Machine, OpTy, PlaceTy}; +use super::{InterpCx, MPlaceTy, Machine, Projectable}; -/// A thing that we can project into, and that has a layout. -/// This wouldn't have to depend on `Machine` but with the current type inference, -/// that's just more convenient to work with (avoids repeating all the `Machine` bounds). -pub trait Value<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>>: Sized { - /// Gets this value's layout. - fn layout(&self) -> TyAndLayout<'tcx>; +/// How to traverse a value and what to do when we are at the leaves. +pub trait ValueVisitor<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>>: Sized { + type V: Projectable<'mir, 'tcx, M::Provenance> + + From<MPlaceTy<'tcx, M::Provenance>> + + std::fmt::Debug; - /// Makes this into an `OpTy`, in a cheap way that is good for reading. - fn to_op_for_read( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>>; - - /// Makes this into an `OpTy`, in a potentially more expensive way that is good for projections. - fn to_op_for_proj( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { - self.to_op_for_read(ecx) - } - - /// Creates this from an `OpTy`. - /// - /// If `to_op_for_proj` only ever produces `Indirect` operands, then this one is definitely `Indirect`. - fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self; - - /// Projects to the given enum variant. - fn project_downcast( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - variant: VariantIdx, - ) -> InterpResult<'tcx, Self>; - - /// Projects to the n-th field. - fn project_field( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - field: usize, - ) -> InterpResult<'tcx, Self>; -} - -/// A thing that we can project into given *mutable* access to `ecx`, and that has a layout. -/// This wouldn't have to depend on `Machine` but with the current type inference, -/// that's just more convenient to work with (avoids repeating all the `Machine` bounds). -pub trait ValueMut<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>>: Sized { - /// Gets this value's layout. - fn layout(&self) -> TyAndLayout<'tcx>; - - /// Makes this into an `OpTy`, in a cheap way that is good for reading. - fn to_op_for_read( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>>; - - /// Makes this into an `OpTy`, in a potentially more expensive way that is good for projections. - fn to_op_for_proj( - &self, - ecx: &mut InterpCx<'mir, 'tcx, M>, - ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>>; - - /// Creates this from an `OpTy`. - /// - /// If `to_op_for_proj` only ever produces `Indirect` operands, then this one is definitely `Indirect`. - fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self; - - /// Projects to the given enum variant. - fn project_downcast( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - variant: VariantIdx, - ) -> InterpResult<'tcx, Self>; - - /// Projects to the n-th field. - fn project_field( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - field: usize, - ) -> InterpResult<'tcx, Self>; -} - -// We cannot have a general impl which shows that Value implies ValueMut. (When we do, it says we -// cannot `impl ValueMut for PlaceTy` because some downstream crate could `impl Value for PlaceTy`.) -// So we have some copy-paste here. (We could have a macro but since we only have 2 types with this -// double-impl, that would barely make the code shorter, if at all.) - -impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> Value<'mir, 'tcx, M> for OpTy<'tcx, M::Provenance> { - #[inline(always)] - fn layout(&self) -> TyAndLayout<'tcx> { - self.layout - } - - #[inline(always)] - fn to_op_for_read( - &self, - _ecx: &InterpCx<'mir, 'tcx, M>, - ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { - Ok(self.clone()) - } - - #[inline(always)] - fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self { - op.clone() - } - - #[inline(always)] - fn project_downcast( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - variant: VariantIdx, - ) -> InterpResult<'tcx, Self> { - ecx.operand_downcast(self, variant) - } - - #[inline(always)] - fn project_field( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - field: usize, - ) -> InterpResult<'tcx, Self> { - ecx.operand_field(self, field) - } -} - -impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueMut<'mir, 'tcx, M> - for OpTy<'tcx, M::Provenance> -{ - #[inline(always)] - fn layout(&self) -> TyAndLayout<'tcx> { - self.layout - } - - #[inline(always)] - fn to_op_for_read( - &self, - _ecx: &InterpCx<'mir, 'tcx, M>, - ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { - Ok(self.clone()) - } - - #[inline(always)] - fn to_op_for_proj( - &self, - _ecx: &mut InterpCx<'mir, 'tcx, M>, - ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { - Ok(self.clone()) - } - - #[inline(always)] - fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self { - op.clone() - } - - #[inline(always)] - fn project_downcast( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - variant: VariantIdx, - ) -> InterpResult<'tcx, Self> { - ecx.operand_downcast(self, variant) - } - - #[inline(always)] - fn project_field( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - field: usize, - ) -> InterpResult<'tcx, Self> { - ecx.operand_field(self, field) - } -} - -impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> Value<'mir, 'tcx, M> - for MPlaceTy<'tcx, M::Provenance> -{ - #[inline(always)] - fn layout(&self) -> TyAndLayout<'tcx> { - self.layout - } - - #[inline(always)] - fn to_op_for_read( - &self, - _ecx: &InterpCx<'mir, 'tcx, M>, - ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { - Ok(self.into()) - } - - #[inline(always)] - fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self { - // assert is justified because our `to_op_for_read` only ever produces `Indirect` operands. - op.assert_mem_place() - } - - #[inline(always)] - fn project_downcast( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - variant: VariantIdx, - ) -> InterpResult<'tcx, Self> { - ecx.mplace_downcast(self, variant) - } - - #[inline(always)] - fn project_field( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - field: usize, - ) -> InterpResult<'tcx, Self> { - ecx.mplace_field(self, field) - } -} - -impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueMut<'mir, 'tcx, M> - for MPlaceTy<'tcx, M::Provenance> -{ - #[inline(always)] - fn layout(&self) -> TyAndLayout<'tcx> { - self.layout - } - - #[inline(always)] - fn to_op_for_read( - &self, - _ecx: &InterpCx<'mir, 'tcx, M>, - ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { - Ok(self.into()) - } - - #[inline(always)] - fn to_op_for_proj( - &self, - _ecx: &mut InterpCx<'mir, 'tcx, M>, - ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { - Ok(self.into()) - } - - #[inline(always)] - fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self { - // assert is justified because our `to_op_for_proj` only ever produces `Indirect` operands. - op.assert_mem_place() - } - - #[inline(always)] - fn project_downcast( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - variant: VariantIdx, - ) -> InterpResult<'tcx, Self> { - ecx.mplace_downcast(self, variant) - } - - #[inline(always)] - fn project_field( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - field: usize, - ) -> InterpResult<'tcx, Self> { - ecx.mplace_field(self, field) - } -} - -impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueMut<'mir, 'tcx, M> - for PlaceTy<'tcx, M::Provenance> -{ - #[inline(always)] - fn layout(&self) -> TyAndLayout<'tcx> { - self.layout - } - - #[inline(always)] - fn to_op_for_read( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { - // No need for `force_allocation` since we are just going to read from this. - ecx.place_to_op(self) - } + /// The visitor must have an `InterpCx` in it. + fn ecx(&self) -> &InterpCx<'mir, 'tcx, M>; + /// `read_discriminant` can be hooked for better error messages. #[inline(always)] - fn to_op_for_proj( - &self, - ecx: &mut InterpCx<'mir, 'tcx, M>, - ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> { - // We `force_allocation` here so that `from_op` below can work. - Ok(ecx.force_allocation(self)?.into()) + fn read_discriminant(&mut self, v: &Self::V) -> InterpResult<'tcx, VariantIdx> { + Ok(self.ecx().read_discriminant(&v.to_op(self.ecx())?)?.1) } - #[inline(always)] - fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self { - // assert is justified because our `to_op` only ever produces `Indirect` operands. - op.assert_mem_place().into() - } - - #[inline(always)] - fn project_downcast( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - variant: VariantIdx, - ) -> InterpResult<'tcx, Self> { - ecx.place_downcast(self, variant) - } - - #[inline(always)] - fn project_field( - &self, - ecx: &InterpCx<'mir, 'tcx, M>, - field: usize, - ) -> InterpResult<'tcx, Self> { - ecx.place_field(self, field) - } -} - -macro_rules! make_value_visitor { - ($visitor_trait:ident, $value_trait:ident, $($mutability:ident)?) => { - /// How to traverse a value and what to do when we are at the leaves. - pub trait $visitor_trait<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>>: Sized { - type V: $value_trait<'mir, 'tcx, M>; - - /// The visitor must have an `InterpCx` in it. - fn ecx(&$($mutability)? self) - -> &$($mutability)? InterpCx<'mir, 'tcx, M>; - - /// `read_discriminant` can be hooked for better error messages. - #[inline(always)] - fn read_discriminant( - &mut self, - op: &OpTy<'tcx, M::Provenance>, - ) -> InterpResult<'tcx, VariantIdx> { - Ok(self.ecx().read_discriminant(op)?.1) - } - - // Recursive actions, ready to be overloaded. - /// Visits the given value, dispatching as appropriate to more specialized visitors. - #[inline(always)] - fn visit_value(&mut self, v: &Self::V) -> InterpResult<'tcx> - { - self.walk_value(v) - } - /// Visits the given value as a union. No automatic recursion can happen here. - #[inline(always)] - fn visit_union(&mut self, _v: &Self::V, _fields: NonZeroUsize) -> InterpResult<'tcx> - { - Ok(()) - } - /// Visits the given value as the pointer of a `Box`. There is nothing to recurse into. - /// The type of `v` will be a raw pointer, but this is a field of `Box<T>` and the - /// pointee type is the actual `T`. - #[inline(always)] - fn visit_box(&mut self, _v: &Self::V) -> InterpResult<'tcx> - { - Ok(()) + /// This function provides the chance to reorder the order in which fields are visited for + /// `FieldsShape::Aggregate`: The order of fields will be + /// `(0..num_fields).map(aggregate_field_order)`. + /// + /// The default means we iterate in source declaration order; alternative this can do an inverse + /// lookup in `memory_index` to use memory field order instead. + #[inline(always)] + fn aggregate_field_order(_memory_index: &IndexVec<FieldIdx, u32>, idx: usize) -> usize { + idx + } + + // Recursive actions, ready to be overloaded. + /// Visits the given value, dispatching as appropriate to more specialized visitors. + #[inline(always)] + fn visit_value(&mut self, v: &Self::V) -> InterpResult<'tcx> { + self.walk_value(v) + } + /// Visits the given value as a union. No automatic recursion can happen here. + #[inline(always)] + fn visit_union(&mut self, _v: &Self::V, _fields: NonZeroUsize) -> InterpResult<'tcx> { + Ok(()) + } + /// Visits the given value as the pointer of a `Box`. There is nothing to recurse into. + /// The type of `v` will be a raw pointer, but this is a field of `Box<T>` and the + /// pointee type is the actual `T`. + #[inline(always)] + fn visit_box(&mut self, _v: &Self::V) -> InterpResult<'tcx> { + Ok(()) + } + + /// Called each time we recurse down to a field of a "product-like" aggregate + /// (structs, tuples, arrays and the like, but not enums), passing in old (outer) + /// and new (inner) value. + /// This gives the visitor the chance to track the stack of nested fields that + /// we are descending through. + #[inline(always)] + fn visit_field( + &mut self, + _old_val: &Self::V, + _field: usize, + new_val: &Self::V, + ) -> InterpResult<'tcx> { + self.visit_value(new_val) + } + /// Called when recursing into an enum variant. + /// This gives the visitor the chance to track the stack of nested fields that + /// we are descending through. + #[inline(always)] + fn visit_variant( + &mut self, + _old_val: &Self::V, + _variant: VariantIdx, + new_val: &Self::V, + ) -> InterpResult<'tcx> { + self.visit_value(new_val) + } + + fn walk_value(&mut self, v: &Self::V) -> InterpResult<'tcx> { + let ty = v.layout().ty; + trace!("walk_value: type: {ty}"); + + // Special treatment for special types, where the (static) layout is not sufficient. + match *ty.kind() { + // If it is a trait object, switch to the real type that was used to create it. + ty::Dynamic(_, _, ty::Dyn) => { + // Dyn types. This is unsized, and the actual dynamic type of the data is given by the + // vtable stored in the place metadata. + // unsized values are never immediate, so we can assert_mem_place + let op = v.to_op(self.ecx())?; + let dest = op.assert_mem_place(); + let inner_mplace = self.ecx().unpack_dyn_trait(&dest)?.0; + trace!("walk_value: dyn object layout: {:#?}", inner_mplace.layout); + // recurse with the inner type + return self.visit_field(&v, 0, &inner_mplace.into()); } - /// Visits this value as an aggregate, you are getting an iterator yielding - /// all the fields (still in an `InterpResult`, you have to do error handling yourself). - /// Recurses into the fields. - #[inline(always)] - fn visit_aggregate( - &mut self, - v: &Self::V, - fields: impl Iterator<Item=InterpResult<'tcx, Self::V>>, - ) -> InterpResult<'tcx> { - self.walk_aggregate(v, fields) + ty::Dynamic(_, _, ty::DynStar) => { + // DynStar types. Very different from a dyn type (but strangely part of the + // same variant in `TyKind`): These are pairs where the 2nd component is the + // vtable, and the first component is the data (which must be ptr-sized). + let data = self.ecx().unpack_dyn_star(v)?.0; + return self.visit_field(&v, 0, &data); } - - /// Called each time we recurse down to a field of a "product-like" aggregate - /// (structs, tuples, arrays and the like, but not enums), passing in old (outer) - /// and new (inner) value. - /// This gives the visitor the chance to track the stack of nested fields that - /// we are descending through. - #[inline(always)] - fn visit_field( - &mut self, - _old_val: &Self::V, - _field: usize, - new_val: &Self::V, - ) -> InterpResult<'tcx> { - self.visit_value(new_val) + // Slices do not need special handling here: they have `Array` field + // placement with length 0, so we enter the `Array` case below which + // indirectly uses the metadata to determine the actual length. + + // However, `Box`... let's talk about `Box`. + ty::Adt(def, ..) if def.is_box() => { + // `Box` is a hybrid primitive-library-defined type that one the one hand is + // a dereferenceable pointer, on the other hand has *basically arbitrary + // user-defined layout* since the user controls the 'allocator' field. So it + // cannot be treated like a normal pointer, since it does not fit into an + // `Immediate`. Yeah, it is quite terrible. But many visitors want to do + // something with "all boxed pointers", so we handle this mess for them. + // + // When we hit a `Box`, we do not do the usual field recursion; instead, + // we (a) call `visit_box` on the pointer value, and (b) recurse on the + // allocator field. We also assert tons of things to ensure we do not miss + // any other fields. + + // `Box` has two fields: the pointer we care about, and the allocator. + assert_eq!(v.layout().fields.count(), 2, "`Box` must have exactly 2 fields"); + let (unique_ptr, alloc) = + (self.ecx().project_field(v, 0)?, self.ecx().project_field(v, 1)?); + // Unfortunately there is some type junk in the way here: `unique_ptr` is a `Unique`... + // (which means another 2 fields, the second of which is a `PhantomData`) + assert_eq!(unique_ptr.layout().fields.count(), 2); + let (nonnull_ptr, phantom) = ( + self.ecx().project_field(&unique_ptr, 0)?, + self.ecx().project_field(&unique_ptr, 1)?, + ); + assert!( + phantom.layout().ty.ty_adt_def().is_some_and(|adt| adt.is_phantom_data()), + "2nd field of `Unique` should be PhantomData but is {:?}", + phantom.layout().ty, + ); + // ... that contains a `NonNull`... (gladly, only a single field here) + assert_eq!(nonnull_ptr.layout().fields.count(), 1); + let raw_ptr = self.ecx().project_field(&nonnull_ptr, 0)?; // the actual raw ptr + // ... whose only field finally is a raw ptr we can dereference. + self.visit_box(&raw_ptr)?; + + // The second `Box` field is the allocator, which we recursively check for validity + // like in regular structs. + self.visit_field(v, 1, &alloc)?; + + // We visited all parts of this one. + return Ok(()); } - /// Called when recursing into an enum variant. - /// This gives the visitor the chance to track the stack of nested fields that - /// we are descending through. - #[inline(always)] - fn visit_variant( - &mut self, - _old_val: &Self::V, - _variant: VariantIdx, - new_val: &Self::V, - ) -> InterpResult<'tcx> { - self.visit_value(new_val) + _ => {} + }; + + // Visit the fields of this value. + match &v.layout().fields { + FieldsShape::Primitive => {} + &FieldsShape::Union(fields) => { + self.visit_union(v, fields)?; } - - // Default recursors. Not meant to be overloaded. - fn walk_aggregate( - &mut self, - v: &Self::V, - fields: impl Iterator<Item=InterpResult<'tcx, Self::V>>, - ) -> InterpResult<'tcx> { - // Now iterate over it. - for (idx, field_val) in fields.enumerate() { - self.visit_field(v, idx, &field_val?)?; + FieldsShape::Arbitrary { offsets, memory_index } => { + for idx in 0..offsets.len() { + let idx = Self::aggregate_field_order(memory_index, idx); + let field = self.ecx().project_field(v, idx)?; + self.visit_field(v, idx, &field)?; } - Ok(()) } - fn walk_value(&mut self, v: &Self::V) -> InterpResult<'tcx> - { - let ty = v.layout().ty; - trace!("walk_value: type: {ty}"); - - // Special treatment for special types, where the (static) layout is not sufficient. - match *ty.kind() { - // If it is a trait object, switch to the real type that was used to create it. - ty::Dynamic(_, _, ty::Dyn) => { - // Dyn types. This is unsized, and the actual dynamic type of the data is given by the - // vtable stored in the place metadata. - // unsized values are never immediate, so we can assert_mem_place - let op = v.to_op_for_read(self.ecx())?; - let dest = op.assert_mem_place(); - let inner_mplace = self.ecx().unpack_dyn_trait(&dest)?.0; - trace!("walk_value: dyn object layout: {:#?}", inner_mplace.layout); - // recurse with the inner type - return self.visit_field(&v, 0, &$value_trait::from_op(&inner_mplace.into())); - }, - ty::Dynamic(_, _, ty::DynStar) => { - // DynStar types. Very different from a dyn type (but strangely part of the - // same variant in `TyKind`): These are pairs where the 2nd component is the - // vtable, and the first component is the data (which must be ptr-sized). - let op = v.to_op_for_proj(self.ecx())?; - let data = self.ecx().unpack_dyn_star(&op)?.0; - return self.visit_field(&v, 0, &$value_trait::from_op(&data)); - } - // Slices do not need special handling here: they have `Array` field - // placement with length 0, so we enter the `Array` case below which - // indirectly uses the metadata to determine the actual length. - - // However, `Box`... let's talk about `Box`. - ty::Adt(def, ..) if def.is_box() => { - // `Box` is a hybrid primitive-library-defined type that one the one hand is - // a dereferenceable pointer, on the other hand has *basically arbitrary - // user-defined layout* since the user controls the 'allocator' field. So it - // cannot be treated like a normal pointer, since it does not fit into an - // `Immediate`. Yeah, it is quite terrible. But many visitors want to do - // something with "all boxed pointers", so we handle this mess for them. - // - // When we hit a `Box`, we do not do the usual `visit_aggregate`; instead, - // we (a) call `visit_box` on the pointer value, and (b) recurse on the - // allocator field. We also assert tons of things to ensure we do not miss - // any other fields. - - // `Box` has two fields: the pointer we care about, and the allocator. - assert_eq!(v.layout().fields.count(), 2, "`Box` must have exactly 2 fields"); - let (unique_ptr, alloc) = - (v.project_field(self.ecx(), 0)?, v.project_field(self.ecx(), 1)?); - // Unfortunately there is some type junk in the way here: `unique_ptr` is a `Unique`... - // (which means another 2 fields, the second of which is a `PhantomData`) - assert_eq!(unique_ptr.layout().fields.count(), 2); - let (nonnull_ptr, phantom) = ( - unique_ptr.project_field(self.ecx(), 0)?, - unique_ptr.project_field(self.ecx(), 1)?, - ); - assert!( - phantom.layout().ty.ty_adt_def().is_some_and(|adt| adt.is_phantom_data()), - "2nd field of `Unique` should be PhantomData but is {:?}", - phantom.layout().ty, - ); - // ... that contains a `NonNull`... (gladly, only a single field here) - assert_eq!(nonnull_ptr.layout().fields.count(), 1); - let raw_ptr = nonnull_ptr.project_field(self.ecx(), 0)?; // the actual raw ptr - // ... whose only field finally is a raw ptr we can dereference. - self.visit_box(&raw_ptr)?; - - // The second `Box` field is the allocator, which we recursively check for validity - // like in regular structs. - self.visit_field(v, 1, &alloc)?; - - // We visited all parts of this one. - return Ok(()); - } - _ => {}, - }; - - // Visit the fields of this value. - match &v.layout().fields { - FieldsShape::Primitive => {} - &FieldsShape::Union(fields) => { - self.visit_union(v, fields)?; - } - FieldsShape::Arbitrary { offsets, .. } => { - // FIXME: We collect in a vec because otherwise there are lifetime - // errors: Projecting to a field needs access to `ecx`. - let fields: Vec<InterpResult<'tcx, Self::V>> = - (0..offsets.len()).map(|i| { - v.project_field(self.ecx(), i) - }) - .collect(); - self.visit_aggregate(v, fields.into_iter())?; - } - FieldsShape::Array { .. } => { - // Let's get an mplace (or immediate) first. - // FIXME: This might `force_allocate` if `v` is a `PlaceTy`! - let op = v.to_op_for_proj(self.ecx())?; - // Now we can go over all the fields. - // This uses the *run-time length*, i.e., if we are a slice, - // the dynamic info from the metadata is used. - let iter = self.ecx().operand_array_fields(&op)? - .map(|f| f.and_then(|f| { - Ok($value_trait::from_op(&f)) - })); - self.visit_aggregate(v, iter)?; - } + FieldsShape::Array { .. } => { + for (idx, field) in self.ecx().project_array_fields(v)?.enumerate() { + self.visit_field(v, idx, &field?)?; } + } + } - match v.layout().variants { - // If this is a multi-variant layout, find the right variant and proceed - // with *its* fields. - Variants::Multiple { .. } => { - let op = v.to_op_for_read(self.ecx())?; - let idx = self.read_discriminant(&op)?; - let inner = v.project_downcast(self.ecx(), idx)?; - trace!("walk_value: variant layout: {:#?}", inner.layout()); - // 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 { .. } => Ok(()) - } + match v.layout().variants { + // If this is a multi-variant layout, find the right variant and proceed + // with *its* fields. + Variants::Multiple { .. } => { + let idx = self.read_discriminant(v)?; + // There are 3 cases where downcasts can turn a Scalar/ScalarPair into a different ABI which + // could be a problem for `ImmTy` (see layout_sanity_check): + // - variant.size == Size::ZERO: works fine because `ImmTy::offset` has a special case for + // zero-sized layouts. + // - variant.fields.count() == 0: works fine because `ImmTy::offset` has a special case for + // zero-field aggregates. + // - variant.abi.is_uninhabited(): triggers UB in `read_discriminant` so we never get here. + let inner = self.ecx().project_downcast(v, idx)?; + trace!("walk_value: variant layout: {:#?}", inner.layout()); + // 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 { .. } => {} } + + Ok(()) } } - -make_value_visitor!(ValueVisitor, Value,); -make_value_visitor!(MutValueVisitor, ValueMut, mut); |