bjoernager/rust
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simplify some code that depend on Deref

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This commit is contained in:
ouz-a 2022-05-12 00:27:06 +03:00
parent 41419e7036
commit c0e4230bf5
3 changed files with 32 additions and 28 deletions
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29
compiler/rustc_mir_transform/src/add_retag.rs
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@ -15,22 +15,13 @@ pub struct AddRetag;
/// (Concurrent accesses by other threads are no problem as these are anyway non-atomic
/// copies. Data races are UB.)
fn is_stable(place: PlaceRef<'_>) -> bool {
place.projection.iter().all(|elem| {
match elem {
// Which place this evaluates to can change with any memory write,
// so cannot assume this to be stable.
ProjectionElem::Deref => false,
// Array indices are interesting, but MIR building generates a *fresh*
// temporary for every array access, so the index cannot be changed as
// a side-effect.
ProjectionElem::Index { .. } |
// The rest is completely boring, they just offset by a constant.
ProjectionElem::Field { .. } |
ProjectionElem::ConstantIndex { .. } |
ProjectionElem::Subslice { .. } |
ProjectionElem::Downcast { .. } => true,
}
})
if place.ret_deref().is_some() {
// Which place this evaluates to can change with any memory write,
// so cannot assume deref to be stable.
return false;
} else {
return true;
}
}
/// Determine whether this type may contain a reference (or box), and thus needs retagging.
@ -91,10 +82,8 @@ impl<'tcx> MirPass<'tcx> for AddRetag {
};
let place_base_raw = |place: &Place<'tcx>| {
// If this is a `Deref`, get the type of what we are deref'ing.
let deref_base =
place.projection.iter().rposition(|p| matches!(p, ProjectionElem::Deref));
if let Some(deref_base) = deref_base {
let base_proj = &place.projection[..deref_base];
if place.ret_deref().is_some() {
let base_proj = &place.projection[..0];
let ty = Place::ty_from(place.local, base_proj, &*local_decls, tcx).ty;
ty.is_unsafe_ptr()
} else {