Merging r348461:

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r348461 | lebedevri | 2018-12-06 00:11:20 -0800 (Thu, 06 Dec 2018) | 4 lines

[NFC][InstCombine] Add more miscompile tests for foldICmpWithLowBitMaskedVal()

We also have to me aware of vector constants. If at least one element
is -1, we can't transform.
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llvm-svn: 348535