[AArch64][test] Improve pr166870.ll test case (#168194)

As pointed out in post-commit discussion on #167336
<https://github.com/llvm/llvm-project/pull/167336#issuecomment-3523794206>,
although the test case succeeds in showing a codegen difference now the
faulty MachineCopyPropagation logic was removed, the example was reduced
so much that it actually would have been legal to remove the seemingly
redundant mov.

This is a re-reduction of that test case which should now demonstrate a
mov that can't safely be removed (mov w9, w9) because the upper bits no
longer being zeroed may alter the program logic.

0 files changed, 0 insertions, 0 deletions