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::mir::interpret::InterpResult;
6 use rustc::ty::layout::{self, TyLayout, VariantIdx};
8 use super::{InterpCx, MPlaceTy, Machine, OpTy};
10 // A thing that we can project into, and that has a layout.
11 // This wouldn't have to depend on `Machine` but with the current type inference,
12 // that's just more convenient to work with (avoids repeating all the `Machine` bounds).
13 pub trait Value<'mir, 'tcx, M: Machine<'mir, 'tcx>>: Copy {
14 /// Gets this value's layout.
15 fn layout(&self) -> TyLayout<'tcx>;
17 /// Makes this into an `OpTy`.
18 fn to_op(self, ecx: &InterpCx<'mir, 'tcx, M>) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>>;
20 /// Creates this from an `MPlaceTy`.
21 fn from_mem_place(mplace: MPlaceTy<'tcx, M::PointerTag>) -> Self;
23 /// Projects to the given enum variant.
26 ecx: &InterpCx<'mir, 'tcx, M>,
28 ) -> InterpResult<'tcx, Self>;
30 /// Projects to the n-th field.
31 fn project_field(self, ecx: &InterpCx<'mir, 'tcx, M>, field: u64) -> InterpResult<'tcx, Self>;
34 // Operands and memory-places are both values.
35 // Places in general are not due to `place_field` having to do `force_allocation`.
36 impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Value<'mir, 'tcx, M> for OpTy<'tcx, M::PointerTag> {
38 fn layout(&self) -> TyLayout<'tcx> {
45 _ecx: &InterpCx<'mir, 'tcx, M>,
46 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
51 fn from_mem_place(mplace: MPlaceTy<'tcx, M::PointerTag>) -> Self {
58 ecx: &InterpCx<'mir, 'tcx, M>,
60 ) -> InterpResult<'tcx, Self> {
61 ecx.operand_downcast(self, variant)
65 fn project_field(self, ecx: &InterpCx<'mir, 'tcx, M>, field: u64) -> InterpResult<'tcx, Self> {
66 ecx.operand_field(self, field)
70 impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Value<'mir, 'tcx, M> for MPlaceTy<'tcx, M::PointerTag> {
72 fn layout(&self) -> TyLayout<'tcx> {
79 _ecx: &InterpCx<'mir, 'tcx, M>,
80 ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
85 fn from_mem_place(mplace: MPlaceTy<'tcx, M::PointerTag>) -> Self {
92 ecx: &InterpCx<'mir, 'tcx, M>,
94 ) -> InterpResult<'tcx, Self> {
95 ecx.mplace_downcast(self, variant)
99 fn project_field(self, ecx: &InterpCx<'mir, 'tcx, M>, field: u64) -> InterpResult<'tcx, Self> {
100 ecx.mplace_field(self, field)
104 macro_rules! make_value_visitor {
105 ($visitor_trait_name:ident, $($mutability:ident)?) => {
106 // How to traverse a value and what to do when we are at the leaves.
107 pub trait $visitor_trait_name<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>>: Sized {
108 type V: Value<'mir, 'tcx, M>;
110 /// The visitor must have an `InterpCx` in it.
111 fn ecx(&$($mutability)? self)
112 -> &$($mutability)? InterpCx<'mir, 'tcx, M>;
114 // Recursive actions, ready to be overloaded.
115 /// Visits the given value, dispatching as appropriate to more specialized visitors.
117 fn visit_value(&mut self, v: Self::V) -> InterpResult<'tcx>
121 /// Visits the given value as a union. No automatic recursion can happen here.
123 fn visit_union(&mut self, _v: Self::V) -> InterpResult<'tcx>
127 /// Visits this value as an aggregate, you are getting an iterator yielding
128 /// all the fields (still in an `InterpResult`, you have to do error handling yourself).
129 /// Recurses into the fields.
134 fields: impl Iterator<Item=InterpResult<'tcx, Self::V>>,
135 ) -> InterpResult<'tcx> {
136 self.walk_aggregate(v, fields)
139 /// Called each time we recurse down to a field of a "product-like" aggregate
140 /// (structs, tuples, arrays and the like, but not enums), passing in old (outer)
141 /// and new (inner) value.
142 /// This gives the visitor the chance to track the stack of nested fields that
143 /// we are descending through.
150 ) -> InterpResult<'tcx> {
151 self.visit_value(new_val)
154 /// Called when recursing into an enum variant.
159 _variant: VariantIdx,
161 ) -> InterpResult<'tcx> {
162 self.visit_value(new_val)
165 /// Called whenever we reach a value with uninhabited layout.
166 /// Recursing to fields will *always* continue after this! This is not meant to control
167 /// whether and how we descend recursively/ into the scalar's fields if there are any,
168 /// it is meant to provide the chance for additional checks when a value of uninhabited
169 /// layout is detected.
171 fn visit_uninhabited(&mut self) -> InterpResult<'tcx>
173 /// Called whenever we reach a value with scalar layout.
174 /// We do NOT provide a `ScalarMaybeUndef` here to avoid accessing memory if the
175 /// visitor is not even interested in scalars.
176 /// Recursing to fields will *always* continue after this! This is not meant to control
177 /// whether and how we descend recursively/ into the scalar's fields if there are any,
178 /// it is meant to provide the chance for additional checks when a value of scalar
179 /// layout is detected.
181 fn visit_scalar(&mut self, _v: Self::V, _layout: &layout::Scalar) -> InterpResult<'tcx>
184 /// Called whenever we reach a value of primitive type. There can be no recursion
185 /// below such a value. This is the leaf function.
186 /// We do *not* provide an `ImmTy` here because some implementations might want
187 /// to write to the place this primitive lives in.
189 fn visit_primitive(&mut self, _v: Self::V) -> InterpResult<'tcx>
192 // Default recursors. Not meant to be overloaded.
196 fields: impl Iterator<Item=InterpResult<'tcx, Self::V>>,
197 ) -> InterpResult<'tcx> {
198 // Now iterate over it.
199 for (idx, field_val) in fields.enumerate() {
200 self.visit_field(v, idx, field_val?)?;
204 fn walk_value(&mut self, v: Self::V) -> InterpResult<'tcx>
206 trace!("walk_value: type: {}", v.layout().ty);
207 // If this is a multi-variant layout, we have to find the right one and proceed with
209 match v.layout().variants {
210 layout::Variants::Multiple { .. } => {
211 let op = v.to_op(self.ecx())?;
212 let idx = self.ecx().read_discriminant(op)?.1;
213 let inner = v.project_downcast(self.ecx(), idx)?;
214 trace!("walk_value: variant layout: {:#?}", inner.layout());
215 // recurse with the inner type
216 return self.visit_variant(v, idx, inner);
218 layout::Variants::Single { .. } => {}
221 // Even for single variants, we might be able to get a more refined type:
222 // If it is a trait object, switch to the actual type that was used to create it.
223 match v.layout().ty.kind {
225 // immediate trait objects are not a thing
226 let dest = v.to_op(self.ecx())?.assert_mem_place(self.ecx());
227 let inner = self.ecx().unpack_dyn_trait(dest)?.1;
228 trace!("walk_value: dyn object layout: {:#?}", inner.layout);
229 // recurse with the inner type
230 return self.visit_field(v, 0, Value::from_mem_place(inner));
232 ty::Generator(..) => {
233 // FIXME: Generator layout is lying: it claims a whole bunch of fields exist
234 // when really many of them can be uninitialized.
235 // Just treat them as a union for now, until hopefully the layout
236 // computation is fixed.
237 return self.visit_union(v);
242 // If this is a scalar, visit it as such.
243 // Things can be aggregates and have scalar layout at the same time, and that
244 // is very relevant for `NonNull` and similar structs: We need to visit them
245 // at their scalar layout *before* descending into their fields.
246 // FIXME: We could avoid some redundant checks here. For newtypes wrapping
247 // scalars, we do the same check on every "level" (e.g., first we check
248 // MyNewtype and then the scalar in there).
249 match v.layout().abi {
250 layout::Abi::Uninhabited => {
251 self.visit_uninhabited()?;
253 layout::Abi::Scalar(ref layout) => {
254 self.visit_scalar(v, layout)?;
256 // FIXME: Should we do something for ScalarPair? Vector?
260 // Check primitive types. We do this after checking the scalar layout,
261 // just to have that done as well. Primitives can have varying layout,
262 // so we check them separately and before aggregate handling.
263 // It is CRITICAL that we get this check right, or we might be
264 // validating the wrong thing!
265 let primitive = match v.layout().fields {
266 // Primitives appear as Union with 0 fields - except for Boxes and fat pointers.
267 layout::FieldPlacement::Union(0) => true,
268 _ => v.layout().ty.builtin_deref(true).is_some(),
271 return self.visit_primitive(v);
274 // Proceed into the fields.
275 match v.layout().fields {
276 layout::FieldPlacement::Union(fields) => {
277 // Empty unions are not accepted by rustc. That's great, it means we can
278 // use that as an unambiguous signal for detecting primitives. Make sure
279 // we did not miss any primitive.
283 layout::FieldPlacement::Arbitrary { ref offsets, .. } => {
284 // FIXME: We collect in a vec because otherwise there are lifetime
285 // errors: Projecting to a field needs access to `ecx`.
286 let fields: Vec<InterpResult<'tcx, Self::V>> =
287 (0..offsets.len()).map(|i| {
288 v.project_field(self.ecx(), i as u64)
291 self.visit_aggregate(v, fields.into_iter())
293 layout::FieldPlacement::Array { .. } => {
294 // Let's get an mplace first.
295 let mplace = v.to_op(self.ecx())?.assert_mem_place(self.ecx());
296 // Now we can go over all the fields.
297 let iter = self.ecx().mplace_array_fields(mplace)?
298 .map(|f| f.and_then(|f| {
299 Ok(Value::from_mem_place(f))
301 self.visit_aggregate(v, iter)
309 make_value_visitor!(ValueVisitor,);
310 make_value_visitor!(MutValueVisitor, mut);