[InstCombine] add getNegativeIsTrueBoolVec() helper function; NFC

Originally part of:
http://reviews.llvm.org/D17485

We need this when simplifying masked memory ops too.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@261483 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed