- Trace through multiple COPYs when looking for a physreg source.
- Add hinting for vregs that will be copied into physregs (we only hinted for vregs getting copied to a physreg previously).
- Give hinted a register a bonus when deciding which value to spill.
This is part of my rewrite regallocfast series. In fact this one doesn't even have an effect unless you also flip the allocation to happen from back to front of a basic block. Nonetheless it helps to split this up to ease review of D52010