src/librustc_mir/dataflow/impls/init_locals.rs

   1 //! A less precise version of `MaybeInitializedPlaces` whose domain is entire locals.
   2 //!
   3 //! A local will be maybe initialized if *any* projections of that local might be initialized.
   4
   5 use crate::dataflow::{self, BottomValue, GenKill};
   6
   7 use rustc_index::bit_set::BitSet;
   8 use rustc_middle::mir::visit::{PlaceContext, Visitor};
   9 use rustc_middle::mir::{self, BasicBlock, Local, Location};
  10
  11 pub struct MaybeInitializedLocals;
  12
  13 impl BottomValue for MaybeInitializedLocals {
  14     /// bottom = uninit
  15     const BOTTOM_VALUE: bool = false;
  16 }
  17
  18 impl dataflow::AnalysisDomain<'tcx> for MaybeInitializedLocals {
  19     type Idx = Local;
  20
  21     const NAME: &'static str = "maybe_init_locals";
  22
  23     fn bits_per_block(&self, body: &mir::Body<'tcx>) -> usize {
  24         body.local_decls.len()
  25     }
  26
  27     fn initialize_start_block(&self, body: &mir::Body<'tcx>, entry_set: &mut BitSet<Self::Idx>) {
  28         // Function arguments are initialized to begin with.
  29         for arg in body.args_iter() {
  30             entry_set.insert(arg);
  31         }
  32     }
  33 }
  34
  35 impl dataflow::GenKillAnalysis<'tcx> for MaybeInitializedLocals {
  36     fn statement_effect(
  37         &self,
  38         trans: &mut impl GenKill<Self::Idx>,
  39         statement: &mir::Statement<'tcx>,
  40         loc: Location,
  41     ) {
  42         TransferFunction { trans }.visit_statement(statement, loc)
  43     }
  44
  45     fn terminator_effect(
  46         &self,
  47         trans: &mut impl GenKill<Self::Idx>,
  48         terminator: &mir::Terminator<'tcx>,
  49         loc: Location,
  50     ) {
  51         TransferFunction { trans }.visit_terminator(terminator, loc)
  52     }
  53
  54     fn call_return_effect(
  55         &self,
  56         trans: &mut impl GenKill<Self::Idx>,
  57         _block: BasicBlock,
  58         _func: &mir::Operand<'tcx>,
  59         _args: &[mir::Operand<'tcx>],
  60         return_place: mir::Place<'tcx>,
  61     ) {
  62         trans.gen(return_place.local)
  63     }
  64
  65     /// See `Analysis::apply_yield_resume_effect`.
  66     fn yield_resume_effect(
  67         &self,
  68         trans: &mut impl GenKill<Self::Idx>,
  69         _resume_block: BasicBlock,
  70         resume_place: mir::Place<'tcx>,
  71     ) {
  72         trans.gen(resume_place.local)
  73     }
  74 }
  75
  76 struct TransferFunction<'a, T> {
  77     trans: &'a mut T,
  78 }
  79
  80 impl<T> Visitor<'tcx> for TransferFunction<'a, T>
  81 where
  82     T: GenKill<Local>,
  83 {
  84     fn visit_local(&mut self, &local: &Local, context: PlaceContext, _: Location) {
  85         use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, NonUseContext};
  86         match context {
  87             // These are handled specially in `call_return_effect` and `yield_resume_effect`.
  88             PlaceContext::MutatingUse(MutatingUseContext::Call | MutatingUseContext::Yield) => {}
  89
  90             // Otherwise, when a place is mutated, we must consider it possibly initialized.
  91             PlaceContext::MutatingUse(_) => self.trans.gen(local),
  92
  93             // If the local is moved out of, or if it gets marked `StorageDead`, consider it no
  94             // longer initialized.
  95             PlaceContext::NonUse(NonUseContext::StorageDead)
  96             | PlaceContext::NonMutatingUse(NonMutatingUseContext::Move) => self.trans.kill(local),
  97
  98             // All other uses do not affect this analysis.
  99             PlaceContext::NonUse(
 100                 NonUseContext::StorageLive
 101                 | NonUseContext::AscribeUserTy
 102                 | NonUseContext::Coverage
 103                 | NonUseContext::VarDebugInfo,
 104             )
 105             | PlaceContext::NonMutatingUse(
 106                 NonMutatingUseContext::Inspect
 107                 | NonMutatingUseContext::Copy
 108                 | NonMutatingUseContext::SharedBorrow
 109                 | NonMutatingUseContext::ShallowBorrow
 110                 | NonMutatingUseContext::UniqueBorrow
 111                 | NonMutatingUseContext::AddressOf
 112                 | NonMutatingUseContext::Projection,
 113             ) => {}
 114         }
 115     }
 116 }