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Add details on truncation and ref-uniq

This commit is contained in:
Aman Arora 2021-08-02 05:12:31 -04:00
parent 55c0829f2c
commit fe03349f87
1 changed files with 17 additions and 10 deletions
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src/types/closure.md
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@ -337,12 +337,12 @@ If a closure captures a field of a composite types such as structs, tuples, and
* Helper functions:
* `unsafe_check(Place, Mode) -> (Place, Mode)`
* "Ensure unsafe accesses occur within the closure"
* If Place contains a deref of a raw pointer:
* Let Place1 = Place truncated just before the deref
* Return (Place1, Mode)
* If Mode is `ref *` and the place contains a field of a packed struct:
* Let Place1 = Place truncated just before the field
* Return (Place1, Mode)
* If Place contains a deref (at index `i`) of a raw pointer:
* Let `(Place1, Mode1) = truncate_place(Place, Mode, i)`
* Return (Place1, Mode1)
* If Mode is `ref *` and the place contains a field of a packed struct at index `i`:
* Let `(Place1, Mode1) = truncate_place(Place, Mode, i)`
* Return (Place1, Mode1)
* Else
* Return (Place, Mode)
* `move_xform(Place, Mode) -> (Place, Mode)` (For move closures)
@ -353,16 +353,16 @@ If a closure captures a field of a composite types such as structs, tuples, and
* Return (Place, Mode)
* Else if Mode is `ref *` and the place contains a deref of an `&`:
* Return (Place, Mode)
* Else if place contains a deref:
* Let Place1 = Place truncated just before the deref
* Else if place contains a deref at index `i`:
* Let `(Place1, _) = truncate_place(Place, Mode, i)`
* Return (Place1, ByValue)
* Else:
* Return (Place, ByValue)
* `ref_xform(Place, Mode) -> (Place, Mode)` (for ref closures)
* "If taking ownership of data, only move data from enclosing stack frame."
* Generate C' by mapping each (Mode, Place) in C
* If Mode is ByValue and place contains a deref:
* Let Place1 = Place truncated just before the deref
* If Mode is ByValue and place contains a deref at index `i`:
* Let `(Place1, _) = truncate_place(Place, Mode, i)`
* Return (Place1, ByValue)
* Else:
* Return (Place, Mode)
@ -378,6 +378,13 @@ If a closure captures a field of a composite types such as structs, tuples, and
and `Place.type_before_projection(l) = ty::Ref(.., Mutability::Not)`
* Let Place1 = (Base, Projections[0..=l])
* Return (Place1, Ref)
* `truncate_place(Place, Mode, len) -> (Place, Mode)`
* "Truncate the place to length `len`, i.e. upto but not including index `len`"
* "If during truncation we drop Deref of a `&mut` and the place was being used by `ref mut`, the access to the truncated place must be unique"
* Let (Proj_before, Proj_after) = Place.split_before(len)
* If Mode == `ref mut` and there exists `Deref` in `Proj_after` at index `i` such that `Place.type_before_projection(len + i)` is `&mut T`
* Return (Place(Proj_before, ..InputPlace), `ref-uniq`)
* Else Return (Place(Proj_before, ..InputPlace), Mode)
## Key examples