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add comment about not using builtin_deref

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This commit is contained in:
Ralf Jung 2018-11-17 12:33:44 +01:00
parent 56f1ef325a
commit c847071355
1 changed files with 4 additions and 0 deletions
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4
src/stacked_borrows.rs
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@ -624,6 +624,8 @@ impl<'a, 'mir, 'tcx> EvalContextExt<'tcx> for MiriEvalContext<'a, 'mir, 'tcx> {
// a `MemPlace`, so we have a fast path for reference types that
// avoids allocating.
match place.layout.ty.sty {
// Cannot use `builtin_deref` because that reports *immutable* for `Box`,
// making it useless.
ty::Ref(_, _, mutbl) => {
// fast path
let val = self.read_immediate(self.place_to_op(place)?)?;
@ -657,6 +659,8 @@ impl<'a, 'mir, 'tcx> EvalContextExt<'tcx> for MiriEvalContext<'a, 'mir, 'tcx> {
// Primitives of reference type, that is the one thing we are interested in.
fn visit_primitive(&mut self, place: MPlaceTy<'tcx, Borrow>) -> EvalResult<'tcx>
{
// Cannot use `builtin_deref` because that reports *immutable* for `Box`,
// making it useless.
let mutbl = match place.layout.ty.sty {
ty::Ref(_, _, mutbl) => mutbl,
ty::Adt(..) if place.layout.ty.is_box() => MutMutable,