--- /dev/null
+//! 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_middle::mir::interpret::InterpResult;
+use rustc_middle::ty;
+use rustc_middle::ty::layout::TyAndLayout;
+use rustc_target::abi::{FieldsShape, VariantIdx, Variants};
+
+use std::num::NonZeroUsize;
+
+use super::{InterpCx, MPlaceTy, Machine, OpTy};
+
+// 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, M: Machine<'mir, 'tcx>>: Copy {
+ /// Gets this value's layout.
+ fn layout(&self) -> TyAndLayout<'tcx>;
+
+ /// Makes this into an `OpTy`.
+ fn to_op(&self, ecx: &InterpCx<'mir, 'tcx, M>)
+ -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>>;
+
+ /// Creates this from an `MPlaceTy`.
+ fn from_mem_place(mplace: MPlaceTy<'tcx, M::PointerTag>) -> 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>;
+}
+
+// Operands and memory-places are both values.
+// Places in general are not due to `place_field` having to do `force_allocation`.
+impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> Value<'mir, 'tcx, M> for OpTy<'tcx, M::PointerTag> {
+ #[inline(always)]
+ fn layout(&self) -> TyAndLayout<'tcx> {
+ self.layout
+ }
+
+ #[inline(always)]
+ fn to_op(
+ &self,
+ _ecx: &InterpCx<'mir, 'tcx, M>,
+ ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
+ Ok(*self)
+ }
+
+ #[inline(always)]
+ fn from_mem_place(mplace: MPlaceTy<'tcx, M::PointerTag>) -> Self {
+ mplace.into()
+ }
+
+ #[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::PointerTag>
+{
+ #[inline(always)]
+ fn layout(&self) -> TyAndLayout<'tcx> {
+ self.layout
+ }
+
+ #[inline(always)]
+ fn to_op(
+ &self,
+ _ecx: &InterpCx<'mir, 'tcx, M>,
+ ) -> InterpResult<'tcx, OpTy<'tcx, M::PointerTag>> {
+ Ok((*self).into())
+ }
+
+ #[inline(always)]
+ fn from_mem_place(mplace: MPlaceTy<'tcx, M::PointerTag>) -> Self {
+ mplace
+ }
+
+ #[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)
+ }
+}
+
+macro_rules! make_value_visitor {
+ ($visitor_trait_name:ident, $($mutability:ident)?) => {
+ // How to traverse a value and what to do when we are at the leaves.
+ pub trait $visitor_trait_name<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>>: Sized {
+ type V: Value<'mir, 'tcx, M>;
+
+ /// The visitor must have an `InterpCx` in it.
+ fn ecx(&$($mutability)? self)
+ -> &$($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::PointerTag>,
+ ) -> 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 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)
+ }
+
+ /// 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)
+ }
+
+ // 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?)?;
+ }
+ Ok(())
+ }
+ fn walk_value(&mut self, v: &Self::V) -> InterpResult<'tcx>
+ {
+ trace!("walk_value: type: {}", v.layout().ty);
+
+ // Special treatment for special types, where the (static) layout is not sufficient.
+ match *v.layout().ty.kind() {
+ // If it is a trait object, switch to the real type that was used to create it.
+ ty::Dynamic(..) => {
+ // immediate trait objects are not a thing
+ let op = v.to_op(self.ecx())?;
+ let dest = op.assert_mem_place();
+ let inner = self.ecx().unpack_dyn_trait(&dest)?.1;
+ trace!("walk_value: dyn object layout: {:#?}", inner.layout);
+ // recurse with the inner type
+ return self.visit_field(&v, 0, &Value::from_mem_place(inner));
+ },
+ // 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.
+ _ => {},
+ };
+
+ // Visit the fields of this value.
+ match v.layout().fields {
+ FieldsShape::Primitive => {},
+ FieldsShape::Union(fields) => {
+ self.visit_union(v, fields)?;
+ },
+ FieldsShape::Arbitrary { ref 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 first.
+ let op = v.to_op(self.ecx())?;
+ let mplace = op.assert_mem_place();
+ // 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().mplace_array_fields(&mplace)?
+ .map(|f| f.and_then(|f| {
+ Ok(Value::from_mem_place(f))
+ }));
+ self.visit_aggregate(v, iter)?;
+ }
+ }
+
+ 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(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(())
+ }
+ }
+ }
+ }
+}
+
+make_value_visitor!(ValueVisitor,);
+make_value_visitor!(MutValueVisitor, mut);
projects / rustc.git / blobdiff