[llvm] r182872 - Teach ReMaterialization to be more cunning about subregisters

[Tim Northover]

> Nice. Is there measurable benefit for any specific target / benchmark?

Hmm, not sure I'm afraid. I suspect x86 has hacks in place to work
around the most glaring problems caused by the deficiency (fixing one
of those was what led me onto it).

I'll see if I can run some numbers tomorrow. It's an interesting question.

Tim.