Cache dependence computation using FoldingSet.

This introduces an LDA-internal DependencePair class. The intention is,
that this is a place where dependence testers can store various results
such as SCEVs describing conflicting iterations, breaking conditions,
distance/direction vectors, etc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76877 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed