LiveIntervalAnalysis: No kill flags for partially undefined uses.
LiveIntervalAnalysis: No kill flags for partially undefined uses.

We must not add kill flags when reading a vreg with some undefined
subregisters, if subreg liveness tracking is enabled.  This is because
the register allocator may reuse these undefined subregisters for other
values which are not killed.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@224664 91177308-0d34-0410-b5e6-96231b3b80d8

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