[Polly][GSoC 2016]Do not process SCoPs with infeasible runtime context

[cs14mtech11017]

Summary

Do not process SCoPs with infeasible runtime context in the new ScopInfoWrapperPass.
Do not compute dependences for such SCoPs in the new DependenceInfoWrapperPass.

[jdoerfert]

lib/Analysis/DependenceInfo.cpp

835

When does this happen exactly? Can't we just prevent it in the ScopInfo pass?

lib/Analysis/ScopInfo.cpp

4280

This looks reasonable and as if it would prevent the problem solved above, doesn't it?

[cs14mtech11017]

lib/Analysis/DependenceInfo.cpp

835

For some SESE Regions, the SCoP does not have a feasible run time context. Hence the SCoP object becomes empty. Placed a null check in this patch in ScopInfoWrapperPass to prevent storing empty SCoPs to the hash map. I think this check is not mandatory, still it is better to have one.

lib/Analysis/ScopInfo.cpp

4280

Yes this solves the problem. Still, it would be advisable to have the other null check as well.

[jdoerfert]

Except the single comment LGTM.

lib/Analysis/DependenceInfo.cpp

835

If it is not expected to ever happen make it an assert please.