Rewrite dest prop.

This fixes a number of correctness issues from the previous version. Additionally, we use a new
strategy which has much better performance charactersitics and also finds more opportunities to
apply the optimization.

compiler/rustc_mir_dataflow/src/impls/init_locals.rs

@@ -1,122 +0,0 @@
-//! A less precise version of `MaybeInitializedPlaces` whose domain is entire locals.
-//!
-//! A local will be maybe initialized if *any* projections of that local might be initialized.
-
-use crate::{CallReturnPlaces, GenKill};
-
-use rustc_index::bit_set::BitSet;
-use rustc_middle::mir::visit::{PlaceContext, Visitor};
-use rustc_middle::mir::{self, BasicBlock, Local, Location};
-
-pub struct MaybeInitializedLocals;
-
-impl<'tcx> crate::AnalysisDomain<'tcx> for MaybeInitializedLocals {
-    type Domain = BitSet<Local>;
-
-    const NAME: &'static str = "maybe_init_locals";
-
-    fn bottom_value(&self, body: &mir::Body<'tcx>) -> Self::Domain {
-        // bottom = uninit
-        BitSet::new_empty(body.local_decls.len())
-    }
-
-    fn initialize_start_block(&self, body: &mir::Body<'tcx>, entry_set: &mut Self::Domain) {
-        // Function arguments are initialized to begin with.
-        for arg in body.args_iter() {
-            entry_set.insert(arg);
-        }
-    }
-}
-
-impl<'tcx> crate::GenKillAnalysis<'tcx> for MaybeInitializedLocals {
-    type Idx = Local;
-
-    fn statement_effect(
-        &self,
-        trans: &mut impl GenKill<Self::Idx>,
-        statement: &mir::Statement<'tcx>,
-        loc: Location,
-    ) {
-        TransferFunction { trans }.visit_statement(statement, loc)
-    }
-
-    fn terminator_effect(
-        &self,
-        trans: &mut impl GenKill<Self::Idx>,
-        terminator: &mir::Terminator<'tcx>,
-        loc: Location,
-    ) {
-        TransferFunction { trans }.visit_terminator(terminator, loc)
-    }
-
-    fn call_return_effect(
-        &self,
-        trans: &mut impl GenKill<Self::Idx>,
-        _block: BasicBlock,
-        return_places: CallReturnPlaces<'_, 'tcx>,
-    ) {
-        return_places.for_each(|place| trans.gen(place.local));
-    }
-
-    /// See `Analysis::apply_yield_resume_effect`.
-    fn yield_resume_effect(
-        &self,
-        trans: &mut impl GenKill<Self::Idx>,
-        _resume_block: BasicBlock,
-        resume_place: mir::Place<'tcx>,
-    ) {
-        trans.gen(resume_place.local)
-    }
-}
-
-struct TransferFunction<'a, T> {
-    trans: &'a mut T,
-}
-
-impl<T> Visitor<'_> for TransferFunction<'_, T>
-where
-    T: GenKill<Local>,
-{
-    // FIXME: Using `visit_local` here is a bug. For example, on `move _5.field` we mark `_5` as
-    // deinitialized, although clearly it is only partially deinitialized. This analysis is not
-    // actually used anywhere at the moment, so this is not critical, but this does need to be fixed
-    // before it starts being used again.
-    fn visit_local(&mut self, local: Local, context: PlaceContext, _: Location) {
-        use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, NonUseContext};
-        match context {
-            // These are handled specially in `call_return_effect` and `yield_resume_effect`.
-            PlaceContext::MutatingUse(
-                MutatingUseContext::Call
-                | MutatingUseContext::AsmOutput
-                | MutatingUseContext::Yield,
-            ) => {}
-
-            // If it's deinitialized, it's no longer init
-            PlaceContext::MutatingUse(MutatingUseContext::Deinit) => self.trans.kill(local),
-
-            // Otherwise, when a place is mutated, we must consider it possibly initialized.
-            PlaceContext::MutatingUse(_) => self.trans.gen(local),
-
-            // If the local is moved out of, or if it gets marked `StorageDead`, consider it no
-            // longer initialized.
-            PlaceContext::NonUse(NonUseContext::StorageDead)
-            | PlaceContext::NonMutatingUse(NonMutatingUseContext::Move) => self.trans.kill(local),
-
-            // All other uses do not affect this analysis.
-            PlaceContext::NonUse(
-                NonUseContext::StorageLive
-                | NonUseContext::AscribeUserTy
-                | NonUseContext::VarDebugInfo,
-            )
-            | PlaceContext::NonMutatingUse(
-                NonMutatingUseContext::Inspect
-                | NonMutatingUseContext::Copy
-                | NonMutatingUseContext::SharedBorrow
-                | NonMutatingUseContext::ShallowBorrow
-                | NonMutatingUseContext::UniqueBorrow
-                | NonMutatingUseContext::AddressOf
-                | NonMutatingUseContext::Projection,
-            ) => {}
-        }
-    }
-}

compiler/rustc_mir_dataflow/src/impls/mod.rs

@@ -19,13 +19,11 @@ use crate::{drop_flag_effects, on_all_children_bits};
 use crate::{lattice, AnalysisDomain, GenKill, GenKillAnalysis};
 
 mod borrowed_locals;
-mod init_locals;
 mod liveness;
 mod storage_liveness;
 
 pub use self::borrowed_locals::borrowed_locals;
 pub use self::borrowed_locals::MaybeBorrowedLocals;
-pub use self::init_locals::MaybeInitializedLocals;
 pub use self::liveness::MaybeLiveLocals;
 pub use self::liveness::MaybeTransitiveLiveLocals;
 pub use self::storage_liveness::{MaybeRequiresStorage, MaybeStorageLive};