compiler/rustc_borrowck/src/def_use.rs

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