Per http://llvm.org/OpenProjects.html#llvm_loopnest, the goal of this patch (and other following patches) is to create facilities that allow implementing loop nest passes that run on top-level loop nests for the New Pass Manager.
This patch extends the functionality of LoopPassManager to handle loop-nest passes by specializing the definition of LoopPassManager that accepts both kinds of passes in addPass.
Only loop passes are executed if L is not a top-level one, and both kinds of passes are executed if L is top-level. Currently, loop nest passes should have the following run method:
PreservedAnalyses run(LoopNest &, LoopAnalysisManager &, LoopStandardAnalysisResults &, LPMUpdater &);