error: Undefined Behavior: attempting a read access using <2170> at alloc1068[0x0], but that tag does not exist in the borrow stack for this location
    --> /home/ben/rust/library/core/src/intrinsics.rs:2103:14
     |
2103 |     unsafe { copy_nonoverlapping(src, dst, count) }
     |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     |              |
     |              attempting a read access using <2170> at alloc1068[0x0], but that tag does not exist in the borrow stack for this location
     |              this error occurs as part of an access at alloc1068[0x0..0x8]
     |
     = help: this indicates a potential bug in the program: it performed an invalid operation, but the rules it violated are still experimental
     = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
help: <2170> was created due to a retag at offsets [0x0..0x10]
    --> ../libcore/src/ptr/mod.rs:640:9
     |
8    | let x = array[0..].as_mut_ptr() as *mut [u32; 2]; // this is `array[0..2]`
     |         ^^^^^^^^^^^^^^^^^^^^^^^
help: <2170> was later invalidated due to a retag at offsets [0x0..0x10]
    --> ../libcore/src/ptr/mod.rs:641:9
     |
9    | let y = array[2..].as_mut_ptr() as *mut [u32; 2]; // this is `array[2..4]`
     |         ^^^^^
     = note: inside `std::intrinsics::copy_nonoverlapping::<[u32; 2]>` at /home/ben/rust/library/core/src/intrinsics.rs:2103:14
     = note: inside `std::ptr::swap::<[u32; 2]>` at /home/ben/rust/library/core/src/ptr/mod.rs:685:9
note: inside `main::_doctest_main____libcore_src_ptr_mod_rs_635_0` at ../libcore/src/ptr/mod.rs:12:5
    --> ../libcore/src/ptr/mod.rs:644:5
     |
12   |     ptr::swap(x, y);
     |     ^^^^^^^^^^^^^^^
note: inside `main` at ../libcore/src/ptr/mod.rs:15:3
    --> ../libcore/src/ptr/mod.rs:647:3
     |
15   | } _doctest_main____libcore_src_ptr_mod_rs_635_0() }
     |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

error: aborting due to previous error