Merging r348462:

Merging r348462:

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r348462 | lebedevri | 2018-12-06 00:14:24 -0800 (Thu, 06 Dec 2018) | 13 lines

[InstCombine] foldICmpWithLowBitMaskedVal(): don't miscompile -1 vector elts

I was finally able to quantify what i thought was missing in the fix,
it was vector constants. If we have a scalar (and %x, -1),
it will be instsimplified before we reach this code,
but if it is a vector, we may still have a -1 element.

Thus, we want to avoid the fold if *at least one* element is -1.
Or in other words, ignoring the undef elements, no sign bits
should be set. Thus, m_NonNegative().

A follow-up for rL348181
https://bugs.llvm.org/show_bug.cgi?id=39861
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_70@348538 91177308-0d34-0410-b5e6-96231b3b80d8