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`.

It then does similar things in various other structs.

compiler/rustc_mir_transform/src/elaborate_drops.rs

@@ -98,9 +98,9 @@ impl<'tcx> crate::MirPass<'tcx> for ElaborateDrops {
 /// Records unwind edges which are known to be unreachable, because they are in `drop` terminators
 /// that can't drop anything.
 #[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>>,
+fn compute_dead_unwinds<'a, 'tcx>(
+    body: &'a Body<'tcx>,
+    flow_inits: &mut ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, '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<'a, 'tcx> {
+    inits: ResultsCursor<'a, 'tcx, MaybeInitializedPlaces<'a, 'tcx>>,
+    uninits: ResultsCursor<'a, 'tcx, MaybeUninitializedPlaces<'a, '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);
@@ -137,24 +137,24 @@ impl InitializationData<'_, '_, '_> {
     }
 }
 
-struct Elaborator<'a, 'b, 'mir, 'tcx> {
-    ctxt: &'a mut ElaborateDropsCtxt<'b, 'mir, 'tcx>,
+struct Elaborator<'a, 'b, 'tcx> {
+    ctxt: &'a mut ElaborateDropsCtxt<'b, 'tcx>,
 }
 
-impl fmt::Debug for Elaborator<'_, '_, '_, '_> {
+impl fmt::Debug for Elaborator<'_, '_, '_> {
     fn fmt(&self, _f: &mut fmt::Formatter<'_>) -> fmt::Result {
         Ok(())
     }
 }
 
-impl<'a, 'tcx> DropElaborator<'a, 'tcx> for Elaborator<'a, '_, '_, 'tcx> {
+impl<'b, 'tcx> DropElaborator<'b, 'tcx> for Elaborator<'_, 'b, 'tcx> {
     type Path = MovePathIndex;
 
     fn patch(&mut self) -> &mut MirPatch<'tcx> {
         &mut self.ctxt.patch
     }
 
-    fn body(&self) -> &'a Body<'tcx> {
+    fn body(&self) -> &'b Body<'tcx> {
         self.ctxt.body
     }
 
@@ -241,17 +241,17 @@ impl<'a, 'tcx> DropElaborator<'a, 'tcx> for Elaborator<'a, '_, '_, 'tcx> {
     }
 }
 
-struct ElaborateDropsCtxt<'a, 'mir, 'tcx> {
+struct ElaborateDropsCtxt<'a, 'tcx> {
     tcx: TyCtxt<'tcx>,
-    body: &'mir Body<'tcx>,
+    body: &'a Body<'tcx>,
     env: &'a MoveDataParamEnv<'tcx>,
-    init_data: InitializationData<'a, 'mir, 'tcx>,
+    init_data: InitializationData<'a, 'tcx>,
     drop_flags: IndexVec<MovePathIndex, Option<Local>>,
     patch: MirPatch<'tcx>,
 }
 
-impl<'b, 'mir, 'tcx> ElaborateDropsCtxt<'b, 'mir, 'tcx> {
-    fn move_data(&self) -> &'b MoveData<'tcx> {
+impl<'a, 'tcx> ElaborateDropsCtxt<'a, 'tcx> {
+    fn move_data(&self) -> &'a MoveData<'tcx> {
         &self.env.move_data
     }