bjoernager/rust
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ensure !Unpin types do not get noalias

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This commit is contained in:
Erik Desjardins 2023-05-20 19:34:31 -04:00
parent 47444d7c25
commit 644818351b
2 changed files with 42 additions and 36 deletions
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36
compiler/rustc_ty_utils/src/abi.rs
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@ -238,7 +238,7 @@ fn adjust_for_rust_scalar<'tcx>(
layout: TyAndLayout<'tcx>,
offset: Size,
is_return: bool,
is_drop_target: bool,
drop_target_pointee: Option<Ty<'tcx>>,
) {
// Booleans are always a noundef i1 that needs to be zero-extended.
if scalar.is_bool() {
@ -252,14 +252,24 @@ fn adjust_for_rust_scalar<'tcx>(
}
// Only pointer types handled below.
let Scalar::Initialized { value: Pointer(_), valid_range} = scalar else { return };
let Scalar::Initialized { value: Pointer(_), valid_range } = scalar else { return };
if !valid_range.contains(0) {
// Set `nonnull` if the validity range excludes zero, or for the argument to `drop_in_place`,
// which must be nonnull per its documented safety requirements.
if !valid_range.contains(0) || drop_target_pointee.is_some() {
attrs.set(ArgAttribute::NonNull);
}
if let Some(pointee) = layout.pointee_info_at(&cx, offset) {
if let Some(kind) = pointee.safe {
let kind = if let Some(kind) = pointee.safe {
Some(kind)
} else if let Some(pointee) = drop_target_pointee {
// The argument to `drop_in_place` is semantically equivalent to a mutable reference.
Some(PointerKind::MutableRef { unpin: pointee.is_unpin(cx.tcx, cx.param_env()) })
} else {
None
};
if let Some(kind) = kind {
attrs.pointee_align = Some(pointee.align);
// `Box` are not necessarily dereferenceable for the entire duration of the function as
@ -307,18 +317,6 @@ fn adjust_for_rust_scalar<'tcx>(
attrs.set(ArgAttribute::ReadOnly);
}
}
// If this is the argument to `drop_in_place`, the contents of which we fully control as the
// compiler, then we mark this argument as `noalias`, aligned, and dereferenceable. (The
// standard library documents the necessary requirements to uphold these attributes for code
// that calls this method directly.) This can enable better optimizations, such as argument
// promotion.
if is_drop_target {
attrs.set(ArgAttribute::NoAlias);
attrs.set(ArgAttribute::NonNull);
attrs.pointee_size = pointee.size;
attrs.pointee_align = Some(pointee.align);
}
}
}
@ -383,6 +381,10 @@ fn fn_abi_new_uncached<'tcx>(
let _entered = span.enter();
let is_return = arg_idx.is_none();
let is_drop_target = is_drop_in_place && arg_idx == Some(0);
let drop_target_pointee = is_drop_target.then(|| match ty.kind() {
ty::RawPtr(ty::TypeAndMut { ty, .. }) => *ty,
_ => bug!("argument to drop_in_place is not a raw ptr: {:?}", ty),
});
let layout = cx.layout_of(ty)?;
let layout = if force_thin_self_ptr && arg_idx == Some(0) {
@ -403,7 +405,7 @@ fn fn_abi_new_uncached<'tcx>(
*layout,
offset,
is_return,
is_drop_target,
drop_target_pointee,
);
attrs
});