rustc_borrowck/
def_use.rs

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1use rustc_middle::bug;
2use rustc_middle::mir::visit::{
3    MutatingUseContext, NonMutatingUseContext, NonUseContext, PlaceContext,
4};
5
6#[derive(Eq, PartialEq, Clone)]
7pub(crate) enum DefUse {
8    Def,
9    Use,
10    Drop,
11}
12
13pub(crate) fn categorize(context: PlaceContext) -> Option<DefUse> {
14    match context {
15        ///////////////////////////////////////////////////////////////////////////
16        // DEFS
17
18        PlaceContext::MutatingUse(MutatingUseContext::Store) |
19
20        // We let Call define the result in both the success and
21        // unwind cases. This is not really correct, however it
22        // does not seem to be observable due to the way that we
23        // generate MIR. To do things properly, we would apply
24        // the def in call only to the input from the success
25        // path and not the unwind path. -nmatsakis
26        PlaceContext::MutatingUse(MutatingUseContext::Call) |
27        PlaceContext::MutatingUse(MutatingUseContext::AsmOutput) |
28        PlaceContext::MutatingUse(MutatingUseContext::Yield) |
29
30        // Storage live and storage dead aren't proper defines, but we can ignore
31        // values that come before them.
32        PlaceContext::NonUse(NonUseContext::StorageLive) |
33        PlaceContext::NonUse(NonUseContext::StorageDead) => Some(DefUse::Def),
34
35        ///////////////////////////////////////////////////////////////////////////
36        // REGULAR USES
37        //
38        // These are uses that occur *outside* of a drop. For the
39        // purposes of NLL, these are special in that **all** the
40        // lifetimes appearing in the variable must be live for each regular use.
41
42        PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection) |
43        PlaceContext::MutatingUse(MutatingUseContext::Projection) |
44
45        // Borrows only consider their local used at the point of the borrow.
46        // This won't affect the results since we use this analysis for coroutines
47        // and we only care about the result at suspension points. Borrows cannot
48        // cross suspension points so this behavior is unproblematic.
49        PlaceContext::MutatingUse(MutatingUseContext::Borrow) |
50        PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow) |
51        PlaceContext::NonMutatingUse(NonMutatingUseContext::FakeBorrow) |
52
53        // `PlaceMention` and `AscribeUserType` both evaluate the place, which must not
54        // contain dangling references.
55        PlaceContext::NonMutatingUse(NonMutatingUseContext::PlaceMention) |
56        PlaceContext::NonUse(NonUseContext::AscribeUserTy(_)) |
57
58        PlaceContext::MutatingUse(MutatingUseContext::RawBorrow) |
59        PlaceContext::NonMutatingUse(NonMutatingUseContext::RawBorrow) |
60        PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect) |
61        PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy) |
62        PlaceContext::NonMutatingUse(NonMutatingUseContext::Move) |
63        PlaceContext::MutatingUse(MutatingUseContext::Retag) =>
64            Some(DefUse::Use),
65
66        ///////////////////////////////////////////////////////////////////////////
67        // DROP USES
68        //
69        // These are uses that occur in a DROP (a MIR drop, not a
70        // call to `std::mem::drop()`). For the purposes of NLL,
71        // uses in drop are special because `#[may_dangle]`
72        // attributes can affect whether lifetimes must be live.
73
74        PlaceContext::MutatingUse(MutatingUseContext::Drop) =>
75            Some(DefUse::Drop),
76
77        // Debug info is neither def nor use.
78        PlaceContext::NonUse(NonUseContext::VarDebugInfo) => None,
79
80        PlaceContext::MutatingUse(MutatingUseContext::Deinit | MutatingUseContext::SetDiscriminant) => {
81            bug!("These statements are not allowed in this MIR phase")
82        }
83    }
84}
rustc_borrowck/def_use.rs

rustc_borrowck/
def_use.rs
