[llvm] r248611 - PeepholeOptimizer: Remove redundant copies

[Charlie Turner via llvm-commits]

Hi Matt,

I'm seeing regressions in our internal benchmarks across Thumb32
targets on ARM after this change.
I'm going to investigate the regressions in more detail, but as of now
it looks like we're getting increased register pressure with this
change, causing extra fills.

Just blowing my horn in advance of further details in case anyone else
has noticed similar regressions.