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LazyCallGraph to support repeated, stable iterations, even in the face of graph updates. This is particularly important to allow the CGSCC pass manager to walk the RefSCCs (and thus everything else) in a module more than once. Lots of unittests and other tests were hard or impossible to write because repeated CGSCC pass managers which didn't invalidate the LazyCallGraph would conclude the module was empty after the first one. =[ Really, really bad. The interesting thing is that in many ways this simplifies the code. We can now re-use the same code for handling reference edge insertion updates of the RefSCC graph as we use for handling call edge insertion updates of the SCC graph. Outside of adapting to the shared logic for this (which isn't trivial, but is *much* simpler than the DFS it replaces!), the new code involves putting newly created RefSCCs when deleting a reference edge into the cached list in the correct way, and to re-formulate the iterator to be stable and effective even in the face of these kinds of updates. I've updated the unittests for the LazyCallGraph to re-iterate the postorder sequence and verify that this all works. We even check for using alternating iterators to trigger the lazy formation of RefSCCs after mutation has occured. It's worth noting that there are a reasonable number of likely simplifications we can make past this. It isn't clear that we need to keep the "LeafRefSCCs" around any more. But I've not removed that mostly because I want this to be a more isolated change. Differential Revision: https://reviews.llvm.org/D24219 llvm-svn: 281716 |
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