Clear old DomainValue after merging.

The old value may still be referenced by some live-out list, and we
don't wan't to collapse those instructions twice.

This fixes the "Can only swizzle VMOVD" assertion in some armv7 SPEC
builds.

<rdar://problem/10413292>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@144117 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed