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make &mut !Unpin not dereferenceable

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See https://github.com/rust-lang/unsafe-code-guidelines/issues/381 for discussion.
This commit is contained in:
Ralf Jung 2022-12-27 12:46:08 +01:00
parent 201ae73872
commit ea541bc2ee
6 changed files with 48 additions and 67 deletions
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15
compiler/rustc_ty_utils/src/abi.rs
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@ -256,13 +256,16 @@ fn adjust_for_rust_scalar<'tcx>(
// `Box` are not necessarily dereferenceable for the entire duration of the function as
// they can be deallocated at any time. Same for non-frozen shared references (see
// <https://github.com/rust-lang/rust/pull/98017>). If LLVM had a way to say
// "dereferenceable on entry" we could use it here.
// <https://github.com/rust-lang/rust/pull/98017>), and for mutable references to
// potentially self-referential types (see
// <https://github.com/rust-lang/unsafe-code-guidelines/issues/381>). If LLVM had a way
// to say "dereferenceable on entry" we could use it here.
attrs.pointee_size = match kind {
PointerKind::Box | PointerKind::SharedRef { frozen: false } => Size::ZERO,
PointerKind::SharedRef { frozen: true } | PointerKind::MutableRef { .. } => {
pointee.size
}
PointerKind::Box
| PointerKind::SharedRef { frozen: false }
| PointerKind::MutableRef { unpin: false } => Size::ZERO,
PointerKind::SharedRef { frozen: true }
| PointerKind::MutableRef { unpin: true } => pointee.size,
};
// The aliasing rules for `Box<T>` are still not decided, but currently we emit