+++ /dev/null
-use rustc_index::bit_set::BitSet;
-use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
-use rustc_middle::mir::{self, Local, Location};
-
-use crate::dataflow::{AnalysisDomain, Backward, GenKill, GenKillAnalysis};
-
-/// A [live-variable dataflow analysis][liveness].
-///
-/// This analysis considers references as being used only at the point of the
-/// borrow. In other words, this analysis does not track uses because of references that already
-/// exist. See [this `mir-dataflow` test][flow-test] for an example. You almost never want to use
-/// this analysis without also looking at the results of [`MaybeBorrowedLocals`].
-///
-/// [`MaybeBorrowedLocals`]: super::MaybeBorrowedLocals
-/// [flow-test]: https://github.com/rust-lang/rust/blob/a08c47310c7d49cbdc5d7afb38408ba519967ecd/src/test/ui/mir-dataflow/liveness-ptr.rs
-/// [liveness]: https://en.wikipedia.org/wiki/Live_variable_analysis
-pub struct MaybeLiveLocals;
-
-impl MaybeLiveLocals {
- fn transfer_function<T>(&self, trans: &'a mut T) -> TransferFunction<'a, T> {
- TransferFunction(trans)
- }
-}
-
-impl AnalysisDomain<'tcx> for MaybeLiveLocals {
- type Domain = BitSet<Local>;
- type Direction = Backward;
-
- const NAME: &'static str = "liveness";
-
- fn bottom_value(&self, body: &mir::Body<'tcx>) -> Self::Domain {
- // bottom = not live
- BitSet::new_empty(body.local_decls.len())
- }
-
- fn initialize_start_block(&self, _: &mir::Body<'tcx>, _: &mut Self::Domain) {
- // No variables are live until we observe a use
- }
-}
-
-impl GenKillAnalysis<'tcx> for MaybeLiveLocals {
- type Idx = Local;
-
- fn statement_effect(
- &self,
- trans: &mut impl GenKill<Self::Idx>,
- statement: &mir::Statement<'tcx>,
- location: Location,
- ) {
- self.transfer_function(trans).visit_statement(statement, location);
- }
-
- fn terminator_effect(
- &self,
- trans: &mut impl GenKill<Self::Idx>,
- terminator: &mir::Terminator<'tcx>,
- location: Location,
- ) {
- self.transfer_function(trans).visit_terminator(terminator, location);
- }
-
- fn call_return_effect(
- &self,
- trans: &mut impl GenKill<Self::Idx>,
- _block: mir::BasicBlock,
- _func: &mir::Operand<'tcx>,
- _args: &[mir::Operand<'tcx>],
- dest_place: mir::Place<'tcx>,
- ) {
- if let Some(local) = dest_place.as_local() {
- trans.kill(local);
- }
- }
-
- fn yield_resume_effect(
- &self,
- trans: &mut impl GenKill<Self::Idx>,
- _resume_block: mir::BasicBlock,
- resume_place: mir::Place<'tcx>,
- ) {
- if let Some(local) = resume_place.as_local() {
- trans.kill(local);
- }
- }
-}
-
-struct TransferFunction<'a, T>(&'a mut T);
-
-impl<'tcx, T> Visitor<'tcx> for TransferFunction<'_, T>
-where
- T: GenKill<Local>,
-{
- fn visit_place(&mut self, place: &mir::Place<'tcx>, context: PlaceContext, location: Location) {
- let mir::Place { projection, local } = *place;
-
- // We purposefully do not call `super_place` here to avoid calling `visit_local` for this
- // place with one of the `Projection` variants of `PlaceContext`.
- self.visit_projection(place.as_ref(), context, location);
-
- match DefUse::for_place(context) {
- // Treat derefs as a use of the base local. `*p = 4` is not a def of `p` but a use.
- Some(_) if place.is_indirect() => self.0.gen(local),
-
- Some(DefUse::Def) if projection.is_empty() => self.0.kill(local),
- Some(DefUse::Use) => self.0.gen(local),
- _ => {}
- }
- }
-
- fn visit_local(&mut self, &local: &Local, context: PlaceContext, _: Location) {
- // Because we do not call `super_place` above, `visit_local` is only called for locals that
- // do not appear as part of a `Place` in the MIR. This handles cases like the implicit use
- // of the return place in a `Return` terminator or the index in an `Index` projection.
- match DefUse::for_place(context) {
- Some(DefUse::Def) => self.0.kill(local),
- Some(DefUse::Use) => self.0.gen(local),
- _ => {}
- }
- }
-}
-
-#[derive(Eq, PartialEq, Clone)]
-enum DefUse {
- Def,
- Use,
-}
-
-impl DefUse {
- fn for_place(context: PlaceContext) -> Option<DefUse> {
- match context {
- PlaceContext::NonUse(_) => None,
-
- PlaceContext::MutatingUse(MutatingUseContext::Store) => Some(DefUse::Def),
-
- // `MutatingUseContext::Call` and `MutatingUseContext::Yield` indicate that this is the
- // destination place for a `Call` return or `Yield` resume respectively. Since this is
- // only a `Def` when the function returns successfully, we handle this case separately
- // in `call_return_effect` above.
- PlaceContext::MutatingUse(MutatingUseContext::Call | MutatingUseContext::Yield) => None,
-
- // All other contexts are uses...
- PlaceContext::MutatingUse(
- MutatingUseContext::AddressOf
- | MutatingUseContext::AsmOutput
- | MutatingUseContext::Borrow
- | MutatingUseContext::Drop
- | MutatingUseContext::Retag,
- )
- | PlaceContext::NonMutatingUse(
- NonMutatingUseContext::AddressOf
- | NonMutatingUseContext::Copy
- | NonMutatingUseContext::Inspect
- | NonMutatingUseContext::Move
- | NonMutatingUseContext::ShallowBorrow
- | NonMutatingUseContext::SharedBorrow
- | NonMutatingUseContext::UniqueBorrow,
- ) => Some(DefUse::Use),
-
- PlaceContext::MutatingUse(MutatingUseContext::Projection)
- | PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection) => {
- unreachable!("A projection could be a def or a use and must be handled separately")
- }
- }
- }
-}
projects / rustc.git / blobdiff