change `BorrowKind::Unique` to be a mutating `PlaceContext` fixes #112056 I believe that `BorrowKind::Unique` is a footgun in general, so I added a FIXME and opened https://github.com/rust-lang/rust/issues/112072. This is a bit too involved for this PR though.
Please read the rustc-dev-guide chapter on Backend Agnostic Codegen.