bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Remove fake borrows of refs that are converted into non-refs in MakeByMoveBody

Browse source
This commit is contained in:
Michael Goulet 2025-03-14 19:38:29 +00:00
parent cbfdf0b014
commit e54bde6d47
4 changed files with 202 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

41
compiler/rustc_mir_transform/src/coroutine/by_move_body.rs
View file

@ -178,7 +178,7 @@ pub(crate) fn coroutine_by_move_body_def_id<'tcx>(
),
};
(
Some((
FieldIdx::from_usize(child_field_idx + num_args),
(
FieldIdx::from_usize(parent_field_idx + num_args),
@ -186,9 +186,10 @@ pub(crate) fn coroutine_by_move_body_def_id<'tcx>(
peel_deref,
child_precise_captures,
),
)
))
},
)
.flatten()
.collect();
if coroutine_kind == ty::ClosureKind::FnOnce {
@ -312,10 +313,46 @@ impl<'tcx> MutVisitor<'tcx> for MakeByMoveBody<'tcx> {
self.super_place(place, context, location);
}
fn visit_statement(&mut self, statement: &mut mir::Statement<'tcx>, location: mir::Location) {
// Remove fake borrows of closure captures if that capture has been
// replaced with a by-move version of that capture.
//
// For example, imagine we capture `Foo` in the parent and `&Foo`
// in the child. We will emit two fake borrows like:
//
// ```
// _2 = &fake shallow (*(_1.0: &Foo));
// _3 = &fake shallow (_1.0: &Foo);
// ```
//
// However, since this transform is responsible for replacing
// `_1.0: &Foo` with `_1.0: Foo`, that makes the second fake borrow
// obsolete, and we should replace it with a nop.
//
// As a side-note, we don't actually even care about fake borrows
// here at all since they're fully a MIR borrowck artifact, and we
// don't need to borrowck by-move MIR bodies. But it's best to preserve
// as much as we can between these two bodies :)
if let mir::StatementKind::Assign(box (_, rvalue)) = &statement.kind
&& let mir::Rvalue::Ref(_, mir::BorrowKind::Fake(mir::FakeBorrowKind::Shallow), place) =
rvalue
&& let mir::PlaceRef {
local: ty::CAPTURE_STRUCT_LOCAL,
projection: [mir::ProjectionElem::Field(idx, _)],
} = place.as_ref()
&& let Some(&(_, _, true, _)) = self.field_remapping.get(&idx)
{
statement.kind = mir::StatementKind::Nop;
}
self.super_statement(statement, location);
}
fn visit_local_decl(&mut self, local: mir::Local, local_decl: &mut mir::LocalDecl<'tcx>) {
// Replace the type of the self arg.
if local == ty::CAPTURE_STRUCT_LOCAL {
local_decl.ty = self.by_move_coroutine_ty;
}
self.super_local_decl(local, local_decl);
}
}