[llvm] [MachineCopyPropagation] Recognise and delete no-op moves produced after forwarded uses (PR #129889)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> Ah - I was hoping you might have looked already, the reproducer is fairly large and you might have known the function to look at.

Nah - I have been hunting to reliably reproduce and pinpoint the bug for a week already; once I had an undisputable reproducer, I wanted to hand it over to someone else :-)

https://github.com/llvm/llvm-project/pull/129889