See http://lists.llvm.org/pipermail/llvm-dev/2018-February/120999.html for llvm-dev discussions
There are six separate instances of getPointerOperand() utility. LoopVectorize.cpp has one of them,
and I don't want to create a 7th one while I'm trying to move LoopVectorizationLegality into a separate file
(eventual objective is to move it to Analysis tree).
I won't insist in having the utility in Instructions.h. Creating include/llvm/IR/InstructionUtils.h is a viable alternative to consider.