error: Undefined Behavior: a SIMD bitmask less than 8 bits long must be filled with 0s for the remaining bits
  --> $DIR/simd-select-bitmask-invalid.rs:LL:CC
   |
LL |         simd_select_bitmask(0b11111111u8, x, x);
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ a SIMD bitmask less than 8 bits long must be filled with 0s for the remaining bits
   |
   = 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 `main` at $DIR/simd-select-bitmask-invalid.rs:LL:CC

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

error: aborting due to previous error