Merging r322319:

Merging r322319:

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r322319 | matze | 2018-01-11 14:30:43 -0800 (Thu, 11 Jan 2018) | 7 lines

PeepholeOptimizer: Fix for vregs without defs

The PeepholeOptimizer would fail for vregs without a definition. If this
was caused by an undef operand abort to keep the code simple (so we
don't need to add logic everywhere to replicate the undef flag).

Differential Revision: https://reviews.llvm.org/D40763
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_60@329619 91177308-0d34-0410-b5e6-96231b3b80d8