[PATCH] [AArch64] Check Dest Resgister Liveness in CondOpt pass

[Z. Zheng]

Hi apazos, t.p.northover, Jiangning, sdmitrouk,

  CondOpt pass does not check for destination register liveness of subs (alias with cmp) instructions.

  Our internal test reveals such case should not be transformed:

    cmp x17, #3
    b.lt .LBB10_15
    ...
    subs x12, x12, #1
    b.gt .LBB10_1

  where x12 is a liveout, becomes:

    cmp x17, #2
    b.le .LBB10_15
    ...
    subs x12, x12, #2
    b.ge .LBB10_1

http://reviews.llvm.org/D6048

Files:
  lib/Target/AArch64/AArch64ConditionOptimizer.cpp
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