src/librustc_mir/dataflow/move_paths/abs_domain.rs

   1 //! The move-analysis portion of borrowck needs to work in an abstract
   2 //! domain of lifted `Place`s. Most of the `Place` variants fall into a
   3 //! one-to-one mapping between the concrete and abstract (e.g., a
   4 //! field-deref on a local variable, `x.field`, has the same meaning
   5 //! in both domains). Indexed projections are the exception: `a[x]`
   6 //! needs to be treated as mapping to the same move path as `a[y]` as
   7 //! well as `a[13]`, etc.
   8 //!
   9 //! (In theory, the analysis could be extended to work with sets of
  10 //! paths, so that `a[0]` and `a[13]` could be kept distinct, while
  11 //! `a[x]` would still overlap them both. But that is not this
  12 //! representation does today.)
  13
  14 use rustc_middle::mir::{Local, Operand, PlaceElem, ProjectionElem};
  15 use rustc_middle::ty::Ty;
  16
  17 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
  18 pub struct AbstractOperand;
  19 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
  20 pub struct AbstractType;
  21 pub type AbstractElem = ProjectionElem<AbstractOperand, AbstractType>;
  22
  23 pub trait Lift {
  24     type Abstract;
  25     fn lift(&self) -> Self::Abstract;
  26 }
  27 impl<'tcx> Lift for Operand<'tcx> {
  28     type Abstract = AbstractOperand;
  29     fn lift(&self) -> Self::Abstract {
  30         AbstractOperand
  31     }
  32 }
  33 impl Lift for Local {
  34     type Abstract = AbstractOperand;
  35     fn lift(&self) -> Self::Abstract {
  36         AbstractOperand
  37     }
  38 }
  39 impl<'tcx> Lift for Ty<'tcx> {
  40     type Abstract = AbstractType;
  41     fn lift(&self) -> Self::Abstract {
  42         AbstractType
  43     }
  44 }
  45 impl<'tcx> Lift for PlaceElem<'tcx> {
  46     type Abstract = AbstractElem;
  47     fn lift(&self) -> Self::Abstract {
  48         match *self {
  49             ProjectionElem::Deref => ProjectionElem::Deref,
  50             ProjectionElem::Field(f, ty) => ProjectionElem::Field(f, ty.lift()),
  51             ProjectionElem::Index(ref i) => ProjectionElem::Index(i.lift()),
  52             ProjectionElem::Subslice { from, to, from_end } => {
  53                 ProjectionElem::Subslice { from, to, from_end }
  54             }
  55             ProjectionElem::ConstantIndex { offset, min_length, from_end } => {
  56                 ProjectionElem::ConstantIndex { offset, min_length, from_end }
  57             }
  58             ProjectionElem::Downcast(a, u) => ProjectionElem::Downcast(a, u),
  59         }
  60     }
  61 }