Merging r277135:

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r277135 | niravd | 2016-07-29 04:49:32 -0700 (Fri, 29 Jul 2016) | 12 lines

Cleanup TransferDbgValues

[DAG] Check debug values for invalidation before transferring and mark
old debug values invalid when transferring to another SDValue.

This fixes PR28613.

Reviewers: jyknight, hans, dblaikie, echristo

Subscribers: yaron.keren, ismail, llvm-commits

Differential Revision: https://reviews.llvm.org/D22858
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llvm-svn: 277164