Struct rustc_mir_dataflow::impls::MaybeUninitializedPlaces

pub struct MaybeUninitializedPlaces<'a, 'tcx> {
    tcx: TyCtxt<'tcx>,
    body: &'a Body<'tcx>,
    mdpe: &'a MoveDataParamEnv<'tcx>,
    mark_inactive_variants_as_uninit: bool,
    skip_unreachable_unwind: BitSet<BasicBlock>,
}

MaybeUninitializedPlaces tracks all places that might be uninitialized upon reaching a particular point in the control flow for a function.

For example, in code like the following, we have corresponding dataflow information shown in the right-hand comments.

struct S;
fn foo(pred: bool) {                        // maybe-uninit:
                                            // {a, b, c, d}
    let a = S; let mut b = S; let c; let d; // {      c, d}

    if pred {
        drop(a);                            // {a,    c, d}
        b = S;                              // {a,    c, d}

    } else {
        drop(b);                            // {   b, c, d}
        d = S;                              // {   b, c   }

    }                                       // {a, b, c, d}

    c = S;                                  // {a, b,    d}
}

To determine whether a place must be uninitialized at a particular control-flow point, one can take the set-difference between this data and the data from MaybeInitializedPlaces at the corresponding control-flow point.

Similarly, at a given drop statement, the set-intersection between this data and MaybeInitializedPlaces yields the set of places that would require a dynamic drop-flag at that statement.

Fields

tcx: TyCtxt<'tcx>

body: &'a Body<'tcx>

mdpe: &'a MoveDataParamEnv<'tcx>

mark_inactive_variants_as_uninit: bool

skip_unreachable_unwind: BitSet<BasicBlock>

Implementations

impl<'a, 'tcx> MaybeUninitializedPlaces<'a, 'tcx>

pub fn new( tcx: TyCtxt<'tcx>, body: &'a Body<'tcx>, mdpe: &'a MoveDataParamEnv<'tcx> ) -> Self

pub fn mark_inactive_variants_as_uninit(self) -> Self

Causes inactive enum variants to be marked as “maybe uninitialized” after a switch on an enum discriminant.

This is correct in a vacuum but is not the default because it causes problems in the borrow checker, where this information gets propagated along FakeEdges.

pub fn skipping_unreachable_unwind( self, unreachable_unwind: BitSet<BasicBlock> ) -> Self

impl<'a, 'tcx> MaybeUninitializedPlaces<'a, 'tcx>

fn update_bits( trans: &mut impl GenKill<MovePathIndex>, path: MovePathIndex, state: DropFlagState )

Trait Implementations

impl<'tcx> AnalysisDomain<'tcx> for MaybeUninitializedPlaces<'_, 'tcx>

type Domain = ChunkedBitSet<MovePathIndex>

There can be many more MovePathIndex than there are locals in a MIR body. We use a chunked bitset to avoid paying too high a memory footprint.

const NAME: &'static str = "maybe_uninit"

A descriptive name for this analysis. Used only for debugging.

fn bottom_value(&self, _: &Body<'tcx>) -> Self::Domain

Returns the initial value of the dataflow state upon entry to each basic block.

fn initialize_start_block(&self, _: &Body<'tcx>, state: &mut Self::Domain)

Mutates the initial value of the dataflow state upon entry to the START_BLOCK.

type Direction = Forward

The direction of this analysis. Either Forward or Backward.

impl<'tcx> GenKillAnalysis<'tcx> for MaybeUninitializedPlaces<'_, 'tcx>

type Idx = MovePathIndex

fn domain_size(&self, _: &Body<'tcx>) -> usize

fn statement_effect( &mut self, trans: &mut impl GenKill<Self::Idx>, _statement: &Statement<'tcx>, location: Location )

See Analysis::apply_statement_effect. Note how the second arg differs.

fn terminator_effect<'mir>( &mut self, trans: &mut Self::Domain, terminator: &'mir Terminator<'tcx>, location: Location ) -> TerminatorEdges<'mir, 'tcx>

See Analysis::apply_terminator_effect.

fn call_return_effect( &mut self, trans: &mut Self::Domain, _block: BasicBlock, return_places: CallReturnPlaces<'_, 'tcx> )

See Analysis::apply_call_return_effect.

fn switch_int_edge_effects<G: GenKill<Self::Idx>>( &mut self, block: BasicBlock, discr: &Operand<'tcx>, edge_effects: &mut impl SwitchIntEdgeEffects<G> )

See Analysis::apply_switch_int_edge_effects.

fn before_statement_effect( &mut self, _trans: &mut impl GenKill<Self::Idx>, _statement: &Statement<'tcx>, _location: Location )

See Analysis::apply_before_statement_effect. Note how the second arg differs.

fn before_terminator_effect( &mut self, _trans: &mut Self::Domain, _terminator: &Terminator<'tcx>, _location: Location )

See Analysis::apply_before_terminator_effect.

impl<'a, 'tcx> HasMoveData<'tcx> for MaybeUninitializedPlaces<'a, 'tcx>

fn move_data(&self) -> &MoveData<'tcx>

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 64 bytes