AArch64: Replace a RegScavenger instance with LivePhysRegs
findScratchNonCalleeSaveRegister() just needs a simple liveness
analysis, use LivePhysRegs for that as it is simpler and does not depend
on the kill flags.
This commit adds a convenience function available() to LivePhysRegs:
This function returns true if the given register is not reserved and
neither the register nor any of its aliases are alive.
Differential Revision: http://reviews.llvm.org/D21865
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@274685
91177308-0d34-0410-b5e6-
96231b3b80d8