Various fixes & minor improvements

[Amanieu]

• Fixed a bug from Adjust Operand encoding #13 with PRegs with index > 32
• Removed regs from MachineEnv since it's not actually needed.
• Return safepoint_slots as Allocations instead of SpillSlots .
  • This enables us to support reftype vregs in register locations in the
    future.
• Removed an unused clobbers vector.

[cfallin]

This all looks reasonable, thanks! The generalization to reftypes-in-Allocation is good and will eventually be useful (for use-cases where the runtime supports it). IIUC, this hasn't changed where refs are actually placed at safepoints though, right? It might be worth adding a note in the safepoint_slots doc-comment noting that for now, all values will be in stackslots, until a future option is added (per-safepoint or for the whole function).

With that change, 👍 from me!

Also, to ensure complete explicitness and clarity, re: the relicensing that is ongoing in #7 currently, you are fine with this contribution being under the new license as well, yes?

Thanks!

[Amanieu]

I've updated the doc comment for safepoint_slots.

And yes, I'm fine with relicensing this as described in #7.

[cfallin]

Thanks!