Bug fixes for CCP

Two fixes to CCP

1. Delay deletion of branches with a constant condition so all unreachable nodes (including these conditions and their projections) are deleted together to avoid leaving uses of deleted nodes.
2. Compute reachability of data nodes as the join of the reachability of its uses so that data nodes in unreachable parts of code are marked unreachable.

requested review from @rarbore2

assigned to @aaronjc4

added 1 commit

• 6ca22828 - Add nested ccp example to CI

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approved this merge request

mentioned in commit e0daecde

merged