[LLVMdev] Loop Info Stability

[David Greene]

I have an analysis pass which uses Scalar Evolution information.  My pass
implements getAnalysisUsage as:

    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      AU.setPreservesAll();
      AU.addRequiredTransitive<LoopInfo>();
      AU.addRequiredTransitive<ScalarEvolution>();
      AU.addRequiredTransitive<TargetData>();
    }

However, I am seeing cases where I'm getting bogus Loop data.  That is,
the Loop object seems to be corrupted (empty block lists, etc.).

At first my pass was a LoopPass because I really only care about the
analysis within loops.  But I thought maybe that's not really correct so I
made it a FunctionPass.  No go, I still see the same issue.

The corruption happens during the running of the analysis itself.

Is there something tricky about the way LoopInfo or SCEV is preserved/not 
preserved?

                                                -Dave