I wasn't able to come up with a minimal example yet, but this was the reason of segfault in #30095

Here's a patch fixing that segfault on 32 bit Linux - petrochenkov@b225678
I.e. segfaults disappear when the deref coercion is not used.

Update: Segfault reproduces on https://github.com/rust-lang/rust/tree/master if impl<T> Deref for P<[T]> is modified to use coercion (fn deref(&self) -> &[T] { &self.ptr }).