Internal compiler error after 'simplify'

[PhilipBorgesen]

Using Futhark 0.20.1 this little piece of silly code produces an internal compiler error irrespective of backend:

entry test [n] (xs: *[n]i32) =
  loop s = ([0i32], xs) for i < n do 
    (copy xs[i:i+1], s.1)

The compiler outputs:

Internal compiler error.
Please report this at https://github.com/diku-dk/futhark/issues.
Type error after pass 'simplify':
In function entry_test
When checking the body aliases: [[], [xs_4626], [xs_4626]]
A unique tuple element of return value of function entry_test is aliased to some other tuple component.

The documentation for copy says

Copy a value. The result will not alias anything.

EDIT: Simplified code sample.