rustc hangs / infinite loop on small example with generic_const_exprs and specialization

This code hangs on nightly

#![feature(specialization)]
#![feature(generic_const_exprs)]

use std::mem;
use std::marker::PhantomData;

trait Repr1 {
  type Elem;
}

struct TypeWithSize<T, const TSize: usize>(PhantomData<T>);

impl<T> Repr1 for TypeWithSize<T, 1> {
  type Elem = u8;
}

impl<T: Sized> Repr1 for T
where
  TypeWithSize<T, { mem::size_of::<T>() }>: Repr1,
{
  type Elem = <TypeWithSize<T, { mem::size_of::<T>() }> as Repr1>::Elem;
}

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=8e9e36d48923272ac7366e521d379170

It works fine if there is a Repr2 to apparently break the cycle

#![feature(specialization)]
#![feature(generic_const_exprs)]
use std::mem;
use std::marker::PhantomData;
trait Repr1 {
  type Elem;
}

struct TypeWithSize<T, const TSize: usize>(PhantomData<T>);

impl<T> Repr1 for TypeWithSize<T, 1> {
  type Elem = u8;
}

trait Repr2 {
  type Elem;
}

impl<T: Sized> Repr2 for T
where
  TypeWithSize<T, { mem::size_of::<T>() }>: Repr1,
{
  type Elem = <TypeWithSize<T, { mem::size_of::<T>() }> as Repr1>::Elem;
}

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=753784ec4df8b6cca783f3d7bbd935b7

Start by compiling the minimal reproducer from the first Rust Playground link on nightly and compare it with the second example, which does not hang. Trace the compiler behavior around specialization and generic_const_exprs; done means the first example no longer loops indefinitely while the related example continues to work.