#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum PointerKind {
- /// Most general case, we know no restrictions to tell LLVM.
- SharedMutable,
-
- /// `&T` where `T` contains no `UnsafeCell`, is `dereferenceable`, `noalias` and `readonly`.
- Frozen,
-
- /// `&mut T` which is `dereferenceable` and `noalias` but not `readonly`.
- UniqueBorrowed,
-
- /// `&mut !Unpin`, which is `dereferenceable` but neither `noalias` nor `readonly`.
- UniqueBorrowedPinned,
-
- /// `Box<T>`, which is `noalias` (even on return types, unlike the above) but neither `readonly`
- /// nor `dereferenceable`.
- UniqueOwned,
+ /// Shared reference. `frozen` indicates the absence of any `UnsafeCell`.
+ SharedRef { frozen: bool },
+ /// Mutable reference. `unpin` indicates the absence of any pinned data.
+ MutableRef { unpin: bool },
+ /// Box.
+ Box,
}
/// Note that this information is advisory only, and backends are free to ignore it.
})
}
ty::Ref(_, ty, mt) if offset.bytes() == 0 => {
- let kind = if tcx.sess.opts.optimize == OptLevel::No {
- // Use conservative pointer kind if not optimizing. This saves us the
- // Freeze/Unpin queries, and can save time in the codegen backend (noalias
- // attributes in LLVM have compile-time cost even in unoptimized builds).
- PointerKind::SharedMutable
- } else {
- match mt {
- hir::Mutability::Not => {
- if ty.is_freeze(tcx, cx.param_env()) {
- PointerKind::Frozen
- } else {
- PointerKind::SharedMutable
- }
- }
- hir::Mutability::Mut => {
- // References to self-referential structures should not be considered
- // noalias, as another pointer to the structure can be obtained, that
- // is not based-on the original reference. We consider all !Unpin
- // types to be potentially self-referential here.
- if ty.is_unpin(tcx, cx.param_env()) {
- PointerKind::UniqueBorrowed
- } else {
- PointerKind::UniqueBorrowedPinned
- }
- }
- }
+ // Use conservative pointer kind if not optimizing. This saves us the
+ // Freeze/Unpin queries, and can save time in the codegen backend (noalias
+ // attributes in LLVM have compile-time cost even in unoptimized builds).
+ let optimize = tcx.sess.opts.optimize != OptLevel::No;
+ let kind = match mt {
+ hir::Mutability::Not => PointerKind::SharedRef {
+ frozen: optimize && ty.is_freeze(tcx, cx.param_env()),
+ },
+ hir::Mutability::Mut => PointerKind::MutableRef {
+ unpin: optimize && ty.is_unpin(tcx, cx.param_env()),
+ },
};
tcx.layout_of(param_env.and(ty)).ok().map(|layout| PointeeInfo {
if let Some(ref mut pointee) = result {
if let ty::Adt(def, _) = this.ty.kind() {
if def.is_box() && offset.bytes() == 0 {
- pointee.safe = Some(PointerKind::UniqueOwned);
+ pointee.safe = Some(PointerKind::Box);
}
}
}
if let Some(kind) = pointee.safe {
attrs.pointee_align = Some(pointee.align);
- // `Box` (`UniqueBorrowed`) are not necessarily dereferenceable
- // for the entire duration of the function as they can be deallocated
- // at any time. Same for shared mutable references. If LLVM had a
- // way to say "dereferenceable on entry" we could use it here.
+ // `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.
attrs.pointee_size = match kind {
- PointerKind::UniqueBorrowed
- | PointerKind::UniqueBorrowedPinned
- | PointerKind::Frozen => pointee.size,
- PointerKind::SharedMutable | PointerKind::UniqueOwned => Size::ZERO,
+ PointerKind::Box | PointerKind::SharedRef { frozen: false } => Size::ZERO,
+ PointerKind::SharedRef { frozen: true } | PointerKind::MutableRef { .. } => {
+ pointee.size
+ }
};
// The aliasing rules for `Box<T>` are still not decided, but currently we emit
// `&mut` pointer parameters never alias other parameters,
// or mutable global data
//
- // `&T` where `T` contains no `UnsafeCell<U>` is immutable,
- // and can be marked as both `readonly` and `noalias`, as
- // LLVM's definition of `noalias` is based solely on memory
- // dependencies rather than pointer equality
+ // `&T` where `T` contains no `UnsafeCell<U>` is immutable, and can be marked as both
+ // `readonly` and `noalias`, as LLVM's definition of `noalias` is based solely on memory
+ // dependencies rather than pointer equality. However this only applies to arguments,
+ // not return values.
let no_alias = match kind {
- PointerKind::SharedMutable | PointerKind::UniqueBorrowedPinned => false,
- PointerKind::UniqueBorrowed => noalias_mut_ref,
- PointerKind::UniqueOwned => noalias_for_box,
- PointerKind::Frozen => true,
+ PointerKind::SharedRef { frozen } => frozen,
+ PointerKind::MutableRef { unpin } => unpin && noalias_mut_ref,
+ PointerKind::Box => noalias_for_box,
};
// We can never add `noalias` in return position; that LLVM attribute has some very surprising semantics
// (see <https://github.com/rust-lang/unsafe-code-guidelines/issues/385#issuecomment-1368055745>).
attrs.set(ArgAttribute::NoAlias);
}
- if kind == PointerKind::Frozen && !is_return {
+ if matches!(kind, PointerKind::SharedRef { frozen: true }) && !is_return {
attrs.set(ArgAttribute::ReadOnly);
}
}
x
}
+// CHECK: align 4 {{i32\*|ptr}} @borrow_mut({{i32\*|ptr}} align 4 %x)
+#[no_mangle]
+pub fn borrow_mut(x: &mut i32) -> &mut i32 {
+ x
+}
+
// CHECK-LABEL: @borrow_call
#[no_mangle]
pub fn borrow_call(x: &i32, f: fn(&i32) -> &i32) -> &i32 {
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