[llvm] [Thumb1] Resolve FIXME: use 'mov hi, $src; mov $dst, hi' (PR #81908)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

(See https://lists.llvm.org/pipermail/llvm-dev/2014-August/075967.html for additional context.)

r10 and r11 are callee-save, so you'd need to make sure they get spilled.  We have code to do the spilling, but it's not triggering here. I guess this code runs too late for that to trigger?

https://github.com/llvm/llvm-project/pull/81908