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

[via llvm-commits]

AtariDreams 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?

r10 - Caller save (in ARM mode, unused in Thumb mode)
r11 Caller save (in ARM mode, unused in Thumb mode)

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