1 //! Visitor for a run-time value with a given layout: Traverse enums, structs and other compound
2 //! types until we arrive at the leaves, with custom handling for primitive types.
4 use rustc_middle::mir::interpret::InterpResult;
6 use rustc_middle::ty::layout::TyAndLayout;
7 use rustc_target::abi::{FieldsShape, VariantIdx, Variants};
9 use std::num::NonZeroUsize;
11 use super::{InterpCx, MPlaceTy, Machine, OpTy, PlaceTy};
13 /// A thing that we can project into, and that has a layout.
14 /// This wouldn't have to depend on `Machine` but with the current type inference,
15 /// that's just more convenient to work with (avoids repeating all the `Machine` bounds).
16 pub trait Value<'mir, 'tcx, M: Machine<'mir, 'tcx>>: Sized {
17 /// Gets this value's layout.
18 fn layout(&self) -> TyAndLayout<'tcx>;
20 /// Makes this into an `OpTy`, in a cheap way that is good for reading.
23 ecx: &InterpCx<'mir, 'tcx, M>,
24 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>>;
26 /// Makes this into an `OpTy`, in a potentially more expensive way that is good for projections.
29 ecx: &InterpCx<'mir, 'tcx, M>,
30 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
31 self.to_op_for_read(ecx)
34 /// Creates this from an `OpTy`.
36 /// If `to_op_for_proj` only ever produces `Indirect` operands, then this one is definitely `Indirect`.
37 fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self;
39 /// Projects to the given enum variant.
42 ecx: &InterpCx<'mir, 'tcx, M>,
44 ) -> InterpResult<'tcx, Self>;
46 /// Projects to the n-th field.
49 ecx: &InterpCx<'mir, 'tcx, M>,
51 ) -> InterpResult<'tcx, Self>;
54 /// A thing that we can project into given *mutable* access to `ecx`, and that has a layout.
55 /// This wouldn't have to depend on `Machine` but with the current type inference,
56 /// that's just more convenient to work with (avoids repeating all the `Machine` bounds).
57 pub trait ValueMut<'mir, 'tcx, M: Machine<'mir, 'tcx>>: Sized {
58 /// Gets this value's layout.
59 fn layout(&self) -> TyAndLayout<'tcx>;
61 /// Makes this into an `OpTy`, in a cheap way that is good for reading.
64 ecx: &InterpCx<'mir, 'tcx, M>,
65 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>>;
67 /// Makes this into an `OpTy`, in a potentially more expensive way that is good for projections.
70 ecx: &mut InterpCx<'mir, 'tcx, M>,
71 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>>;
73 /// Creates this from an `OpTy`.
75 /// If `to_op_for_proj` only ever produces `Indirect` operands, then this one is definitely `Indirect`.
76 fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self;
78 /// Projects to the given enum variant.
81 ecx: &mut InterpCx<'mir, 'tcx, M>,
83 ) -> InterpResult<'tcx, Self>;
85 /// Projects to the n-th field.
88 ecx: &mut InterpCx<'mir, 'tcx, M>,
90 ) -> InterpResult<'tcx, Self>;
93 // We cannot have a general impl which shows that Value implies ValueMut. (When we do, it says we
94 // cannot `impl ValueMut for PlaceTy` because some downstream crate could `impl Value for PlaceTy`.)
95 // So we have some copy-paste here. (We could have a macro but since we only have 2 types with this
96 // double-impl, that would barely make the code shorter, if at all.)
98 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> Value<'mir, 'tcx, M> for OpTy<'tcx, M::Provenance> {
100 fn layout(&self) -> TyAndLayout<'tcx> {
107 _ecx: &InterpCx<'mir, 'tcx, M>,
108 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
113 fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self {
120 ecx: &InterpCx<'mir, 'tcx, M>,
122 ) -> InterpResult<'tcx, Self> {
123 ecx.operand_downcast(self, variant)
129 ecx: &InterpCx<'mir, 'tcx, M>,
131 ) -> InterpResult<'tcx, Self> {
132 ecx.operand_field(self, field)
136 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueMut<'mir, 'tcx, M>
137 for OpTy<'tcx, M::Provenance>
140 fn layout(&self) -> TyAndLayout<'tcx> {
147 _ecx: &InterpCx<'mir, 'tcx, M>,
148 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
155 _ecx: &mut InterpCx<'mir, 'tcx, M>,
156 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
161 fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self {
168 ecx: &mut InterpCx<'mir, 'tcx, M>,
170 ) -> InterpResult<'tcx, Self> {
171 ecx.operand_downcast(self, variant)
177 ecx: &mut InterpCx<'mir, 'tcx, M>,
179 ) -> InterpResult<'tcx, Self> {
180 ecx.operand_field(self, field)
184 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> Value<'mir, 'tcx, M>
185 for MPlaceTy<'tcx, M::Provenance>
188 fn layout(&self) -> TyAndLayout<'tcx> {
195 _ecx: &InterpCx<'mir, 'tcx, M>,
196 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
201 fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self {
202 // assert is justified because our `to_op_for_read` only ever produces `Indirect` operands.
203 op.assert_mem_place()
209 ecx: &InterpCx<'mir, 'tcx, M>,
211 ) -> InterpResult<'tcx, Self> {
212 ecx.mplace_downcast(self, variant)
218 ecx: &InterpCx<'mir, 'tcx, M>,
220 ) -> InterpResult<'tcx, Self> {
221 ecx.mplace_field(self, field)
225 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueMut<'mir, 'tcx, M>
226 for MPlaceTy<'tcx, M::Provenance>
229 fn layout(&self) -> TyAndLayout<'tcx> {
236 _ecx: &InterpCx<'mir, 'tcx, M>,
237 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
244 _ecx: &mut InterpCx<'mir, 'tcx, M>,
245 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
250 fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self {
251 // assert is justified because our `to_op_for_proj` only ever produces `Indirect` operands.
252 op.assert_mem_place()
258 ecx: &mut InterpCx<'mir, 'tcx, M>,
260 ) -> InterpResult<'tcx, Self> {
261 ecx.mplace_downcast(self, variant)
267 ecx: &mut InterpCx<'mir, 'tcx, M>,
269 ) -> InterpResult<'tcx, Self> {
270 ecx.mplace_field(self, field)
274 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueMut<'mir, 'tcx, M>
275 for PlaceTy<'tcx, M::Provenance>
278 fn layout(&self) -> TyAndLayout<'tcx> {
285 ecx: &InterpCx<'mir, 'tcx, M>,
286 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
287 // We `force_allocation` here so that `from_op` below can work.
288 ecx.place_to_op(self)
294 ecx: &mut InterpCx<'mir, 'tcx, M>,
295 ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
296 // We `force_allocation` here so that `from_op` below can work.
297 Ok(ecx.force_allocation(self)?.into())
301 fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self {
302 // assert is justified because our `to_op` only ever produces `Indirect` operands.
303 op.assert_mem_place().into()
309 ecx: &mut InterpCx<'mir, 'tcx, M>,
311 ) -> InterpResult<'tcx, Self> {
312 ecx.place_downcast(self, variant)
318 ecx: &mut InterpCx<'mir, 'tcx, M>,
320 ) -> InterpResult<'tcx, Self> {
321 ecx.place_field(self, field)
325 macro_rules! make_value_visitor {
326 ($visitor_trait:ident, $value_trait:ident, $($mutability:ident)?) => {
327 // How to traverse a value and what to do when we are at the leaves.
328 pub trait $visitor_trait<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>>: Sized {
329 type V: $value_trait<'mir, 'tcx, M>;
331 /// The visitor must have an `InterpCx` in it.
332 fn ecx(&$($mutability)? self)
333 -> &$($mutability)? InterpCx<'mir, 'tcx, M>;
335 /// `read_discriminant` can be hooked for better error messages.
337 fn read_discriminant(
339 op: &OpTy<'tcx, M::Provenance>,
340 ) -> InterpResult<'tcx, VariantIdx> {
341 Ok(self.ecx().read_discriminant(op)?.1)
344 // Recursive actions, ready to be overloaded.
345 /// Visits the given value, dispatching as appropriate to more specialized visitors.
347 fn visit_value(&mut self, v: &Self::V) -> InterpResult<'tcx>
351 /// Visits the given value as a union. No automatic recursion can happen here.
353 fn visit_union(&mut self, _v: &Self::V, _fields: NonZeroUsize) -> InterpResult<'tcx>
357 /// Visits the given value as the pointer of a `Box`. There is nothing to recurse into.
358 /// The type of `v` will be a raw pointer, but this is a field of `Box<T>` and the
359 /// pointee type is the actual `T`.
361 fn visit_box(&mut self, _v: &Self::V) -> InterpResult<'tcx>
365 /// Visits this value as an aggregate, you are getting an iterator yielding
366 /// all the fields (still in an `InterpResult`, you have to do error handling yourself).
367 /// Recurses into the fields.
372 fields: impl Iterator<Item=InterpResult<'tcx, Self::V>>,
373 ) -> InterpResult<'tcx> {
374 self.walk_aggregate(v, fields)
377 /// Called each time we recurse down to a field of a "product-like" aggregate
378 /// (structs, tuples, arrays and the like, but not enums), passing in old (outer)
379 /// and new (inner) value.
380 /// This gives the visitor the chance to track the stack of nested fields that
381 /// we are descending through.
388 ) -> InterpResult<'tcx> {
389 self.visit_value(new_val)
391 /// Called when recursing into an enum variant.
392 /// This gives the visitor the chance to track the stack of nested fields that
393 /// we are descending through.
398 _variant: VariantIdx,
400 ) -> InterpResult<'tcx> {
401 self.visit_value(new_val)
404 // Default recursors. Not meant to be overloaded.
408 fields: impl Iterator<Item=InterpResult<'tcx, Self::V>>,
409 ) -> InterpResult<'tcx> {
410 // Now iterate over it.
411 for (idx, field_val) in fields.enumerate() {
412 self.visit_field(v, idx, &field_val?)?;
416 fn walk_value(&mut self, v: &Self::V) -> InterpResult<'tcx>
418 let ty = v.layout().ty;
419 trace!("walk_value: type: {ty}");
421 // Special treatment for special types, where the (static) layout is not sufficient.
423 // If it is a trait object, switch to the real type that was used to create it.
425 // unsized values are never immediate, so we can assert_mem_place
426 let op = v.to_op_for_read(self.ecx())?;
427 let dest = op.assert_mem_place();
428 let inner_mplace = self.ecx().unpack_dyn_trait(&dest)?;
429 trace!("walk_value: dyn object layout: {:#?}", inner_mplace.layout);
430 // recurse with the inner type
431 return self.visit_field(&v, 0, &$value_trait::from_op(&inner_mplace.into()));
433 // Slices do not need special handling here: they have `Array` field
434 // placement with length 0, so we enter the `Array` case below which
435 // indirectly uses the metadata to determine the actual length.
437 // However, `Box`... let's talk about `Box`.
438 ty::Adt(def, ..) if def.is_box() => {
439 // `Box` is a hybrid primitive-library-defined type that one the one hand is
440 // a dereferenceable pointer, on the other hand has *basically arbitrary
441 // user-defined layout* since the user controls the 'allocator' field. So it
442 // cannot be treated like a normal pointer, since it does not fit into an
443 // `Immediate`. Yeah, it is quite terrible. But many visitors want to do
444 // something with "all boxed pointers", so we handle this mess for them.
446 // When we hit a `Box`, we do not do the usual `visit_aggregate`; instead,
447 // we (a) call `visit_box` on the pointer value, and (b) recurse on the
448 // allocator field. We also assert tons of things to ensure we do not miss
451 // `Box` has two fields: the pointer we care about, and the allocator.
452 assert_eq!(v.layout().fields.count(), 2, "`Box` must have exactly 2 fields");
453 let (unique_ptr, alloc) =
454 (v.project_field(self.ecx(), 0)?, v.project_field(self.ecx(), 1)?);
455 // Unfortunately there is some type junk in the way here: `unique_ptr` is a `Unique`...
456 // (which means another 2 fields, the second of which is a `PhantomData`)
457 assert_eq!(unique_ptr.layout().fields.count(), 2);
458 let (nonnull_ptr, phantom) = (
459 unique_ptr.project_field(self.ecx(), 0)?,
460 unique_ptr.project_field(self.ecx(), 1)?,
463 phantom.layout().ty.ty_adt_def().is_some_and(|adt| adt.is_phantom_data()),
464 "2nd field of `Unique` should be PhantomData but is {:?}",
467 // ... that contains a `NonNull`... (gladly, only a single field here)
468 assert_eq!(nonnull_ptr.layout().fields.count(), 1);
469 let raw_ptr = nonnull_ptr.project_field(self.ecx(), 0)?; // the actual raw ptr
470 // ... whose only field finally is a raw ptr we can dereference.
471 self.visit_box(&raw_ptr)?;
473 // The second `Box` field is the allocator, which we recursively check for validity
474 // like in regular structs.
475 self.visit_field(v, 1, &alloc)?;
477 // We visited all parts of this one.
483 // Visit the fields of this value.
484 match v.layout().fields {
485 FieldsShape::Primitive => {}
486 FieldsShape::Union(fields) => {
487 self.visit_union(v, fields)?;
489 FieldsShape::Arbitrary { ref offsets, .. } => {
490 // FIXME: We collect in a vec because otherwise there are lifetime
491 // errors: Projecting to a field needs access to `ecx`.
492 let fields: Vec<InterpResult<'tcx, Self::V>> =
493 (0..offsets.len()).map(|i| {
494 v.project_field(self.ecx(), i)
497 self.visit_aggregate(v, fields.into_iter())?;
499 FieldsShape::Array { .. } => {
500 // Let's get an mplace (or immediate) first.
501 // This might `force_allocate` if `v` is a `PlaceTy`, but `place_index` does that anyway.
502 let op = v.to_op_for_proj(self.ecx())?;
503 // Now we can go over all the fields.
504 // This uses the *run-time length*, i.e., if we are a slice,
505 // the dynamic info from the metadata is used.
506 let iter = self.ecx().operand_array_fields(&op)?
507 .map(|f| f.and_then(|f| {
508 Ok($value_trait::from_op(&f))
510 self.visit_aggregate(v, iter)?;
514 match v.layout().variants {
515 // If this is a multi-variant layout, find the right variant and proceed
516 // with *its* fields.
517 Variants::Multiple { .. } => {
518 let op = v.to_op_for_read(self.ecx())?;
519 let idx = self.read_discriminant(&op)?;
520 let inner = v.project_downcast(self.ecx(), idx)?;
521 trace!("walk_value: variant layout: {:#?}", inner.layout());
522 // recurse with the inner type
523 self.visit_variant(v, idx, &inner)
525 // For single-variant layouts, we already did anything there is to do.
526 Variants::Single { .. } => Ok(())
533 make_value_visitor!(ValueVisitor, Value,);
534 make_value_visitor!(MutValueVisitor, ValueMut, mut);