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use rustc_middle::mir::*;
use rustc_middle::ty::{self, TyCtxt};
use rustc_target::abi::Align;
/// Returns `true` if this place is allowed to be less aligned
/// than its containing struct (because it is within a packed
/// struct).
pub fn is_disaligned<'tcx, L>(
tcx: TyCtxt<'tcx>,
local_decls: &L,
param_env: ty::ParamEnv<'tcx>,
place: Place<'tcx>,
) -> bool
where
L: HasLocalDecls<'tcx>,
{
debug!("is_disaligned({:?})", place);
let Some(pack) = is_within_packed(tcx, local_decls, place) else {
debug!("is_disaligned({:?}) - not within packed", place);
return false;
};
let ty = place.ty(local_decls, tcx).ty;
match tcx.layout_of(param_env.and(ty)) {
Ok(layout) if layout.align.abi <= pack => {
// If the packed alignment is greater or equal to the field alignment, the type won't be
// further disaligned.
debug!(
"is_disaligned({:?}) - align = {}, packed = {}; not disaligned",
place,
layout.align.abi.bytes(),
pack.bytes()
);
false
}
_ => {
debug!("is_disaligned({:?}) - true", place);
true
}
}
}
fn is_within_packed<'tcx, L>(
tcx: TyCtxt<'tcx>,
local_decls: &L,
place: Place<'tcx>,
) -> Option<Align>
where
L: HasLocalDecls<'tcx>,
{
place
.iter_projections()
.rev()
// Stop at `Deref`; standard ABI alignment applies there.
.take_while(|(_base, elem)| !matches!(elem, ProjectionElem::Deref))
// Consider the packed alignments at play here...
.filter_map(|(base, _elem)| {
base.ty(local_decls, tcx).ty.ty_adt_def().and_then(|adt| adt.repr().pack)
})
// ... and compute their minimum.
// The overall smallest alignment is what matters.
.min()
}
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