Remove unnecessary lifetimes in dataflow structs.

There are four related dataflow structs: `MaybeInitializedPlaces`,
`MaybeUninitializedPlaces`, and `EverInitializedPlaces`,
`DefinitelyInitializedPlaces`. They all have a `&Body` and a
`&MoveData<'tcx>` field. The first three use different lifetimes for the
two fields, but the last one uses the same lifetime for both.

This commit changes the first three to use the same lifetime, removing
the need for one of the lifetimes. Other structs that also lose a
lifetime as a result of this are `LivenessContext`, `LivenessResults`,
`InitializationData`.

The commit uses the name `'mir` everywhere for the lifetimes used with
`&Body` and `&MoveData`, replacing some other names: `'a`, `'flow`, and
`'cx`. I think this is a reasonable name because `'mir' is used for many
`mir::Body` references (and things within `mir::Body`). Even when a
lifetime is shared between a `&Body` and a reference to something else,
the `'mir` lifetime name is so well-established that it's reasonable to
reuse it, rather than something non-specific like `'a`. (Naming
lifetimes is hard!)

Author: nnethercote

compiler/rustc_borrowck/src/dataflow.rs

@@ -17,16 +17,16 @@ use crate::{places_conflict, BorrowSet, PlaceConflictBias, PlaceExt, RegionInfer
 /// The results of the dataflow analyses used by the borrow checker.
 pub(crate) struct BorrowckResults<'a, 'mir, 'tcx> {
     pub(crate) borrows: Results<'tcx, Borrows<'a, 'mir, 'tcx>>,
-    pub(crate) uninits: Results<'tcx, MaybeUninitializedPlaces<'a, 'mir, 'tcx>>,
-    pub(crate) ever_inits: Results<'tcx, EverInitializedPlaces<'a, 'mir, 'tcx>>,
+    pub(crate) uninits: Results<'tcx, MaybeUninitializedPlaces<'mir, 'tcx>>,
+    pub(crate) ever_inits: Results<'tcx, EverInitializedPlaces<'mir, 'tcx>>,
 }
 
 /// The transient state of the dataflow analyses used by the borrow checker.
 #[derive(Debug)]
 pub(crate) struct BorrowckFlowState<'a, 'mir, 'tcx> {
     pub(crate) borrows: <Borrows<'a, 'mir, 'tcx> as AnalysisDomain<'tcx>>::Domain,
-    pub(crate) uninits: <MaybeUninitializedPlaces<'a, 'mir, 'tcx> as AnalysisDomain<'tcx>>::Domain,
-    pub(crate) ever_inits: <EverInitializedPlaces<'a, 'mir, 'tcx> as AnalysisDomain<'tcx>>::Domain,
+    pub(crate) uninits: <MaybeUninitializedPlaces<'mir, 'tcx> as AnalysisDomain<'tcx>>::Domain,
+    pub(crate) ever_inits: <EverInitializedPlaces<'mir, 'tcx> as AnalysisDomain<'tcx>>::Domain,
 }
 
 impl<'a, 'mir, 'tcx> ResultsVisitable<'tcx> for BorrowckResults<'a, 'mir, 'tcx> {

compiler/rustc_borrowck/src/nll.rs

@@ -75,14 +75,14 @@ pub(crate) fn replace_regions_in_mir<'tcx>(
 /// Computes the (non-lexical) regions from the input MIR.
 ///
 /// This may result in errors being reported.
-pub(crate) fn compute_regions<'cx, 'tcx>(
+pub(crate) fn compute_regions<'mir, 'tcx>(
     infcx: &BorrowckInferCtxt<'tcx>,
     universal_regions: UniversalRegions<'tcx>,
     body: &Body<'tcx>,
     promoted: &IndexSlice<Promoted, Body<'tcx>>,
     location_table: &LocationTable,
     param_env: ty::ParamEnv<'tcx>,
-    flow_inits: &mut ResultsCursor<'cx, 'tcx, MaybeInitializedPlaces<'_, 'cx, 'tcx>>,
+    flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
     move_data: &MoveData<'tcx>,
     borrow_set: &BorrowSet<'tcx>,
     upvars: &[&ty::CapturedPlace<'tcx>],

compiler/rustc_borrowck/src/type_check/liveness/mod.rs

@@ -34,7 +34,7 @@ pub(super) fn generate<'mir, 'tcx>(
     typeck: &mut TypeChecker<'_, 'tcx>,
     body: &Body<'tcx>,
     elements: &Rc<DenseLocationMap>,
-    flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'_, 'mir, 'tcx>>,
+    flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
     move_data: &MoveData<'tcx>,
 ) {
     debug!("liveness::generate");

compiler/rustc_borrowck/src/type_check/liveness/trace.rs

@@ -41,7 +41,7 @@ pub(super) fn trace<'mir, 'tcx>(
     typeck: &mut TypeChecker<'_, 'tcx>,
     body: &Body<'tcx>,
     elements: &Rc<DenseLocationMap>,
-    flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'_, 'mir, 'tcx>>,
+    flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
     move_data: &MoveData<'tcx>,
     relevant_live_locals: Vec<Local>,
     boring_locals: Vec<Local>,
@@ -99,7 +99,7 @@ pub(super) fn trace<'mir, 'tcx>(
 }
 
 /// Contextual state for the type-liveness coroutine.
-struct LivenessContext<'a, 'me, 'typeck, 'flow, 'tcx> {
+struct LivenessContext<'me, 'typeck, 'mir, 'tcx> {
     /// Current type-checker, giving us our inference context etc.
     typeck: &'me mut TypeChecker<'typeck, 'tcx>,
 
@@ -117,7 +117,7 @@ struct LivenessContext<'a, 'me, 'typeck, 'flow, 'tcx> {
 
     /// Results of dataflow tracking which variables (and paths) have been
     /// initialized.
-    flow_inits: &'me mut ResultsCursor<'flow, 'tcx, MaybeInitializedPlaces<'a, 'flow, 'tcx>>,
+    flow_inits: &'me mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
 
     /// Index indicating where each variable is assigned, used, or
     /// dropped.
@@ -129,8 +129,8 @@ struct DropData<'tcx> {
     region_constraint_data: Option<&'tcx QueryRegionConstraints<'tcx>>,
 }
 
-struct LivenessResults<'a, 'me, 'typeck, 'flow, 'tcx> {
-    cx: LivenessContext<'a, 'me, 'typeck, 'flow, 'tcx>,
+struct LivenessResults<'me, 'typeck, 'mir, 'tcx> {
+    cx: LivenessContext<'me, 'typeck, 'mir, 'tcx>,
 
     /// Set of points that define the current local.
     defs: BitSet<PointIndex>,
@@ -151,8 +151,8 @@ struct LivenessResults<'a, 'me, 'typeck, 'flow, 'tcx> {
     stack: Vec<PointIndex>,
 }
 
-impl<'a, 'me, 'typeck, 'flow, 'tcx> LivenessResults<'a, 'me, 'typeck, 'flow, 'tcx> {
-    fn new(cx: LivenessContext<'a, 'me, 'typeck, 'flow, 'tcx>) -> Self {
+impl<'me, 'typeck, 'mir, 'tcx> LivenessResults<'me, 'typeck, 'mir, 'tcx> {
+    fn new(cx: LivenessContext<'me, 'typeck, 'mir, 'tcx>) -> Self {
         let num_points = cx.elements.num_points();
         LivenessResults {
             cx,
@@ -505,7 +505,7 @@ impl<'a, 'me, 'typeck, 'flow, 'tcx> LivenessResults<'a, 'me, 'typeck, 'flow, 'tc
     }
 }
 
-impl<'tcx> LivenessContext<'_, '_, '_, '_, 'tcx> {
+impl<'tcx> LivenessContext<'_, '_, '_, 'tcx> {
     /// Returns `true` if the local variable (or some part of it) is initialized at the current
     /// cursor position. Callers should call one of the `seek` methods immediately before to point
     /// the cursor to the desired location.

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -125,7 +125,7 @@ pub(crate) fn type_check<'mir, 'tcx>(
     location_table: &LocationTable,
     borrow_set: &BorrowSet<'tcx>,
     all_facts: &mut Option<AllFacts>,
-    flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'_, 'mir, 'tcx>>,
+    flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
     move_data: &MoveData<'tcx>,
     elements: &Rc<DenseLocationMap>,
     upvars: &[&ty::CapturedPlace<'tcx>],

compiler/rustc_mir_dataflow/src/impls/initialized.rs

@@ -51,15 +51,15 @@ use crate::{
 /// Similarly, at a given `drop` statement, the set-intersection
 /// between this data and `MaybeUninitializedPlaces` yields the set of
 /// places that would require a dynamic drop-flag at that statement.
-pub struct MaybeInitializedPlaces<'a, 'mir, 'tcx> {
+pub struct MaybeInitializedPlaces<'mir, 'tcx> {
     tcx: TyCtxt<'tcx>,
     body: &'mir Body<'tcx>,
-    move_data: &'a MoveData<'tcx>,
+    move_data: &'mir MoveData<'tcx>,
     skip_unreachable_unwind: bool,
 }
 
-impl<'a, 'mir, 'tcx> MaybeInitializedPlaces<'a, 'mir, 'tcx> {
-    pub fn new(tcx: TyCtxt<'tcx>, body: &'mir Body<'tcx>, move_data: &'a MoveData<'tcx>) -> Self {
+impl<'mir, 'tcx> MaybeInitializedPlaces<'mir, 'tcx> {
+    pub fn new(tcx: TyCtxt<'tcx>, body: &'mir Body<'tcx>, move_data: &'mir MoveData<'tcx>) -> Self {
         MaybeInitializedPlaces { tcx, body, move_data, skip_unreachable_unwind: false }
     }
 
@@ -85,7 +85,7 @@ impl<'a, 'mir, 'tcx> MaybeInitializedPlaces<'a, 'mir, 'tcx> {
     }
 }
 
-impl<'a, 'mir, 'tcx> HasMoveData<'tcx> for MaybeInitializedPlaces<'a, 'mir, 'tcx> {
+impl<'mir, 'tcx> HasMoveData<'tcx> for MaybeInitializedPlaces<'mir, 'tcx> {
     fn move_data(&self) -> &MoveData<'tcx> {
         self.move_data
     }
@@ -126,17 +126,17 @@ impl<'a, 'mir, 'tcx> HasMoveData<'tcx> for MaybeInitializedPlaces<'a, 'mir, 'tcx
 /// 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.
-pub struct MaybeUninitializedPlaces<'a, 'mir, 'tcx> {
+pub struct MaybeUninitializedPlaces<'mir, 'tcx> {
     tcx: TyCtxt<'tcx>,
     body: &'mir Body<'tcx>,
-    move_data: &'a MoveData<'tcx>,
+    move_data: &'mir MoveData<'tcx>,
 
     mark_inactive_variants_as_uninit: bool,
     skip_unreachable_unwind: BitSet<mir::BasicBlock>,
 }
 
-impl<'a, 'mir, 'tcx> MaybeUninitializedPlaces<'a, 'mir, 'tcx> {
-    pub fn new(tcx: TyCtxt<'tcx>, body: &'mir Body<'tcx>, move_data: &'a MoveData<'tcx>) -> Self {
+impl<'mir, 'tcx> MaybeUninitializedPlaces<'mir, 'tcx> {
+    pub fn new(tcx: TyCtxt<'tcx>, body: &'mir Body<'tcx>, move_data: &'mir MoveData<'tcx>) -> Self {
         MaybeUninitializedPlaces {
             tcx,
             body,
@@ -165,7 +165,7 @@ impl<'a, 'mir, 'tcx> MaybeUninitializedPlaces<'a, 'mir, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> HasMoveData<'tcx> for MaybeUninitializedPlaces<'a, '_, 'tcx> {
+impl<'tcx> HasMoveData<'tcx> for MaybeUninitializedPlaces<'_, 'tcx> {
     fn move_data(&self) -> &MoveData<'tcx> {
         self.move_data
     }
@@ -205,18 +205,18 @@ impl<'a, 'tcx> HasMoveData<'tcx> for MaybeUninitializedPlaces<'a, '_, 'tcx> {
 /// Similarly, at a given `drop` statement, the set-difference between
 /// this data and `MaybeInitializedPlaces` yields the set of places
 /// that would require a dynamic drop-flag at that statement.
-pub struct DefinitelyInitializedPlaces<'a, 'tcx> {
-    body: &'a Body<'tcx>,
-    move_data: &'a MoveData<'tcx>,
+pub struct DefinitelyInitializedPlaces<'mir, 'tcx> {
+    body: &'mir Body<'tcx>,
+    move_data: &'mir MoveData<'tcx>,
 }
 
-impl<'a, 'tcx> DefinitelyInitializedPlaces<'a, 'tcx> {
-    pub fn new(body: &'a Body<'tcx>, move_data: &'a MoveData<'tcx>) -> Self {
+impl<'mir, 'tcx> DefinitelyInitializedPlaces<'mir, 'tcx> {
+    pub fn new(body: &'mir Body<'tcx>, move_data: &'mir MoveData<'tcx>) -> Self {
         DefinitelyInitializedPlaces { body, move_data }
     }
 }
 
-impl<'a, 'tcx> HasMoveData<'tcx> for DefinitelyInitializedPlaces<'a, 'tcx> {
+impl<'mir, 'tcx> HasMoveData<'tcx> for DefinitelyInitializedPlaces<'mir, 'tcx> {
     fn move_data(&self) -> &MoveData<'tcx> {
         self.move_data
     }
@@ -251,24 +251,24 @@ impl<'a, 'tcx> HasMoveData<'tcx> for DefinitelyInitializedPlaces<'a, 'tcx> {
 ///     c = S;                                  // {a, b, c, d }
 /// }
 /// ```
-pub struct EverInitializedPlaces<'a, 'mir, 'tcx> {
+pub struct EverInitializedPlaces<'mir, 'tcx> {
     body: &'mir Body<'tcx>,
-    move_data: &'a MoveData<'tcx>,
+    move_data: &'mir MoveData<'tcx>,
 }
 
-impl<'a, 'mir, 'tcx> EverInitializedPlaces<'a, 'mir, 'tcx> {
-    pub fn new(body: &'mir Body<'tcx>, move_data: &'a MoveData<'tcx>) -> Self {
+impl<'mir, 'tcx> EverInitializedPlaces<'mir, 'tcx> {
+    pub fn new(body: &'mir Body<'tcx>, move_data: &'mir MoveData<'tcx>) -> Self {
         EverInitializedPlaces { body, move_data }
     }
 }
 
-impl<'a, 'tcx> HasMoveData<'tcx> for EverInitializedPlaces<'a, '_, 'tcx> {
+impl<'tcx> HasMoveData<'tcx> for EverInitializedPlaces<'_, 'tcx> {
     fn move_data(&self) -> &MoveData<'tcx> {
         self.move_data
     }
 }
 
-impl<'a, 'mir, 'tcx> MaybeInitializedPlaces<'a, 'mir, 'tcx> {
+impl<'mir, 'tcx> MaybeInitializedPlaces<'mir, 'tcx> {
     fn update_bits(
         trans: &mut impl GenKill<MovePathIndex>,
         path: MovePathIndex,
@@ -281,7 +281,7 @@ impl<'a, 'mir, 'tcx> MaybeInitializedPlaces<'a, 'mir, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> MaybeUninitializedPlaces<'a, '_, 'tcx> {
+impl<'tcx> MaybeUninitializedPlaces<'_, 'tcx> {
     fn update_bits(
         trans: &mut impl GenKill<MovePathIndex>,
         path: MovePathIndex,
@@ -294,7 +294,7 @@ impl<'a, 'tcx> MaybeUninitializedPlaces<'a, '_, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> DefinitelyInitializedPlaces<'a, 'tcx> {
+impl<'mir, 'tcx> DefinitelyInitializedPlaces<'mir, 'tcx> {
     fn update_bits(
         trans: &mut impl GenKill<MovePathIndex>,
         path: MovePathIndex,
@@ -307,7 +307,7 @@ impl<'a, 'tcx> DefinitelyInitializedPlaces<'a, 'tcx> {
     }
 }
 
-impl<'tcx> AnalysisDomain<'tcx> for MaybeInitializedPlaces<'_, '_, 'tcx> {
+impl<'tcx> AnalysisDomain<'tcx> for MaybeInitializedPlaces<'_, 'tcx> {
     /// 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.
     type Domain = MaybeReachable<ChunkedBitSet<MovePathIndex>>;
@@ -329,7 +329,7 @@ impl<'tcx> AnalysisDomain<'tcx> for MaybeInitializedPlaces<'_, '_, 'tcx> {
     }
 }
 
-impl<'tcx> GenKillAnalysis<'tcx> for MaybeInitializedPlaces<'_, '_, 'tcx> {
+impl<'tcx> GenKillAnalysis<'tcx> for MaybeInitializedPlaces<'_, 'tcx> {
     type Idx = MovePathIndex;
 
     fn domain_size(&self, _: &Body<'tcx>) -> usize {
@@ -442,7 +442,7 @@ impl<'tcx> GenKillAnalysis<'tcx> for MaybeInitializedPlaces<'_, '_, 'tcx> {
     }
 }
 
-impl<'tcx> AnalysisDomain<'tcx> for MaybeUninitializedPlaces<'_, '_, 'tcx> {
+impl<'tcx> AnalysisDomain<'tcx> for MaybeUninitializedPlaces<'_, 'tcx> {
     /// 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.
     type Domain = ChunkedBitSet<MovePathIndex>;
@@ -466,7 +466,7 @@ impl<'tcx> AnalysisDomain<'tcx> for MaybeUninitializedPlaces<'_, '_, 'tcx> {
     }
 }
 
-impl<'tcx> GenKillAnalysis<'tcx> for MaybeUninitializedPlaces<'_, '_, 'tcx> {
+impl<'tcx> GenKillAnalysis<'tcx> for MaybeUninitializedPlaces<'_, 'tcx> {
     type Idx = MovePathIndex;
 
     fn domain_size(&self, _: &Body<'tcx>) -> usize {
@@ -571,7 +571,7 @@ impl<'tcx> GenKillAnalysis<'tcx> for MaybeUninitializedPlaces<'_, '_, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> AnalysisDomain<'tcx> for DefinitelyInitializedPlaces<'a, 'tcx> {
+impl<'mir, 'tcx> AnalysisDomain<'tcx> for DefinitelyInitializedPlaces<'mir, 'tcx> {
     /// Use set intersection as the join operator.
     type Domain = lattice::Dual<BitSet<MovePathIndex>>;
 
@@ -643,7 +643,7 @@ impl<'tcx> GenKillAnalysis<'tcx> for DefinitelyInitializedPlaces<'_, 'tcx> {
     }
 }
 
-impl<'tcx> AnalysisDomain<'tcx> for EverInitializedPlaces<'_, '_, 'tcx> {
+impl<'tcx> AnalysisDomain<'tcx> for EverInitializedPlaces<'_, 'tcx> {
     /// There can be many more `InitIndex` than there are locals in a MIR body.
     /// We use a chunked bitset to avoid paying too high a memory footprint.
     type Domain = ChunkedBitSet<InitIndex>;
@@ -662,7 +662,7 @@ impl<'tcx> AnalysisDomain<'tcx> for EverInitializedPlaces<'_, '_, 'tcx> {
     }
 }
 
-impl<'tcx> GenKillAnalysis<'tcx> for EverInitializedPlaces<'_, '_, 'tcx> {
+impl<'tcx> GenKillAnalysis<'tcx> for EverInitializedPlaces<'_, 'tcx> {
     type Idx = InitIndex;
 
     fn domain_size(&self, _: &Body<'tcx>) -> usize {

compiler/rustc_mir_transform/src/elaborate_drops.rs

@@ -100,7 +100,7 @@ impl<'tcx> crate::MirPass<'tcx> for ElaborateDrops {
 #[instrument(level = "trace", skip(body, flow_inits), ret)]
 fn compute_dead_unwinds<'mir, 'tcx>(
     body: &'mir Body<'tcx>,
-    flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'_, 'mir, 'tcx>>,
+    flow_inits: &mut ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
 ) -> BitSet<BasicBlock> {
     // We only need to do this pass once, because unwind edges can only
     // reach cleanup blocks, which can't have unwind edges themselves.
@@ -121,12 +121,12 @@ fn compute_dead_unwinds<'mir, 'tcx>(
     dead_unwinds
 }
 
-struct InitializationData<'a, 'mir, 'tcx> {
-    inits: ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'a, 'mir, 'tcx>>,
-    uninits: ResultsCursor<'mir, 'tcx, MaybeUninitializedPlaces<'a, 'mir, 'tcx>>,
+struct InitializationData<'mir, 'tcx> {
+    inits: ResultsCursor<'mir, 'tcx, MaybeInitializedPlaces<'mir, 'tcx>>,
+    uninits: ResultsCursor<'mir, 'tcx, MaybeUninitializedPlaces<'mir, 'tcx>>,
 }
 
-impl InitializationData<'_, '_, '_> {
+impl InitializationData<'_, '_> {
     fn seek_before(&mut self, loc: Location) {
         self.inits.seek_before_primary_effect(loc);
         self.uninits.seek_before_primary_effect(loc);
@@ -245,7 +245,7 @@ struct ElaborateDropsCtxt<'a, 'mir, 'tcx> {
     tcx: TyCtxt<'tcx>,
     body: &'mir Body<'tcx>,
     env: &'a MoveDataParamEnv<'tcx>,
-    init_data: InitializationData<'a, 'mir, 'tcx>,
+    init_data: InitializationData<'mir, 'tcx>,
     drop_flags: IndexVec<MovePathIndex, Option<Local>>,
     patch: MirPatch<'tcx>,
 }