compiler/rustc_borrowck/src/def_use.rs

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