SIV/MIV classification for LDA.

SIV/MIV classification for LDA.

LoopDependenceAnalysis::getLoops is currently O(N*M) for a loop-nest of
depth N and a compound SCEV of M atomic SCEVs. As both N and M will
typically be very small, this should not be a problem. If it turns out
to be one, rewriting getLoops as SCEVVisitor will reduce complexity to
O(M).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78394 91177308-0d34-0410-b5e6-96231b3b80d8