Merge DerefArgVisitor and PinArgVisitor.

They are almost identical, differing only in the `ProjectionElem` they
insert. This commit merges them into a new type `SelfArgVisitor`.

Author: nnethercote

compiler/rustc_mir_transform/src/coroutine.rs

@@ -112,11 +112,12 @@ impl<'tcx> MutVisitor<'tcx> for RenameLocalVisitor<'tcx> {
 }
 }
 
-structDerefArgVisitor<'tcx>{
+structSelfArgVisitor<'tcx>{
+elem:ProjectionElem<Local,Ty<'tcx>>,
 tcx:TyCtxt<'tcx>,
 }
 
-impl<'tcx>MutVisitor<'tcx>forDerefArgVisitor<'tcx>{
+impl<'tcx>MutVisitor<'tcx>forSelfArgVisitor<'tcx>{
 fntcx(&self) -> TyCtxt<'tcx>{
 self.tcx
 }
@@ -129,49 +130,7 @@ impl<'tcx> MutVisitor<'tcx> for DerefArgVisitor<'tcx> {
 if place.local == SELF_ARG{
 replace_base(
  place,
-Place{
-local:SELF_ARG,
-projection:self.tcx().mk_place_elems(&[ProjectionElem::Deref]),
-},
-self.tcx,
-);
-}else{
-self.visit_local(&mut place.local, context, location);
-
-for elem in place.projection.iter(){
-ifletPlaceElem::Index(local) = elem {
-assert_ne!(local,SELF_ARG);
-}
-}
-}
-}
-}
-
-structPinArgVisitor<'tcx>{
-ref_coroutine_ty:Ty<'tcx>,
-tcx:TyCtxt<'tcx>,
-}
-
-impl<'tcx>MutVisitor<'tcx>forPinArgVisitor<'tcx>{
-fntcx(&self) -> TyCtxt<'tcx>{
-self.tcx
-}
-
-fnvisit_local(&mutself,local:&mutLocal, _:PlaceContext, _:Location){
-assert_ne!(*local,SELF_ARG);
-}
-
-fnvisit_place(&mutself,place:&mutPlace<'tcx>,context:PlaceContext,location:Location){
-if place.local == SELF_ARG{
-replace_base(
- place,
-Place{
-local:SELF_ARG,
-projection:self.tcx().mk_place_elems(&[ProjectionElem::Field(
-FieldIdx::ZERO,
-self.ref_coroutine_ty,
-)]),
-},
+Place{local:SELF_ARG,projection:self.tcx().mk_place_elems(&[self.elem])},
 self.tcx,
 );
 }else{
@@ -568,7 +527,7 @@ fn make_coroutine_state_argument_indirect<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Bo
  body.local_decls.raw[1].ty = ref_coroutine_ty;
 
 // Add a deref to accesses of the coroutine state
-DerefArgVisitor{ tcx }.visit_body(body);
+SelfArgVisitor{ tcx,elem:ProjectionElem::Deref}.visit_body(body);
 }
 
 fnmake_coroutine_state_argument_pinned<'tcx>(tcx:TyCtxt<'tcx>,body:&mutBody<'tcx>){
@@ -583,7 +542,8 @@ fn make_coroutine_state_argument_pinned<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body
  body.local_decls.raw[1].ty = pin_ref_coroutine_ty;
 
 // Add the Pin field access to accesses of the coroutine state
-PinArgVisitor{ ref_coroutine_ty, tcx }.visit_body(body);
+SelfArgVisitor{ tcx,elem:ProjectionElem::Field(FieldIdx::ZERO, ref_coroutine_ty)}
+.visit_body(body);
 }
 
 /// Allocates a new local and replaces all references of `local` with it. Returns the new local.