error: Undefined Behavior: reading memory at ALLOC[0x0..0x10], but memory is uninitialized at [0x4..0x10], and this operation requires initialized memory
  --> RUSTLIB/core/src/slice/cmp.rs:LL:CC
   |
LL |         let mut order = unsafe { compare_bytes(left, right, len) as isize };
   |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
   |
   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
   = note: BACKTRACE:
   = note: inside `<u8 as core::slice::cmp::SliceOrd>::compare` at RUSTLIB/core/src/slice/cmp.rs:LL:CC
   = note: inside `core::slice::cmp::<impl std::cmp::Ord for [u8]>::cmp` at RUSTLIB/core/src/slice/cmp.rs:LL:CC
note: inside `main`
  --> tests/fail/uninit/uninit_alloc_diagnostic.rs:LL:CC
   |
LL |         drop(slice1.cmp(slice2));
   |              ^^^^^^^^^^^^^^^^^^

Uninitialized memory occurred at ALLOC[0x4..0x10], in this allocation:
ALLOC (Rust heap, size: 32, align: 8) {
    0x00 │ 41 42 43 44 __ __ __ __ __ __ __ __ __ __ __ __ │ ABCD░░░░░░░░░░░░
    0x10 │ 00 __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ │ .░░░░░░░░░░░░░░░
}

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

error: aborting due to 1 previous error