Restoring latest patch.

@mkazantsev, would you mind taking one more look at this patch? One significant fix was made since your last review, to handle duplicate edges from SwitchInsts. The patch has now been rebased to latest (which hasn't changed it much). Thanks!

Did not include the reverted part of the code (the important part :) ) in the new patch. Added separate testcase for switch-backedge. Thanks for the fix suggestions.

Keep the InLoopPredecessors vector in the original order.

Missed the sort call -- thanks.

Remove duplicate blocks from the list of exit predecessors. This happens when the predecessor inst is a switch with duplicate targets. Avoids block double-processing and maintains the metadata consistency assertion.

Sorry for the trouble. I'll figure out what happened.

Thank you for the thorough review. I have one more request to the reviewers on this list: could someone give a hand to commit the code? I don't have write access to the repo yet.

Previous patch was null, this is the right one.

Rewrote comments, fixed formatting, simplified test and added checks for specific metadata

One more favor to ask: Could I please have some help committing this fix? I'm new to the project and don't have write access yet...

Thanks! I've made the suggested test change.