RegisterScavenging: Followup to r305625
This does some improvements/cleanup to the recently introduced
scavengeRegisterBackwards() functionality:
- Rewrite findSurvivorBackwards algorithm to use the existing
LiveRegUnit::accumulateBackward() code. This also avoids the Available
and Candidates bitset and just need 1 LiveRegUnit instance
(= 1 bitset).
- Pick registers in allocation order instead of register number order.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305817
91177308-0d34-0410-b5e6-
96231b3b80d8
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