[PATCH] D43216: [Dominators] Ensure that every PostDomTree root is connected to the virtual node

Jakub Kuderski via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Mon Feb 12 19:03:09 PST 2018

kuhar added a comment.

In https://reviews.llvm.org/D43216#1005844, @brzycki wrote:

> Hi @kuhar , is there a testcase that causes this to fail?

I was only able to make it fail by manually updating the tree; this doesn't catch the recent update error reported by @dmgreen. It just made me notice that we are missing this check.
This is actually quite annoying, because with postdominators there can be multiple correct tree and the checks that we currently have are not able to ensure that after the sequence we always arrive to the same tree. For now, the other patch (https://reviews.llvm.org/D43140) makes the verifier do the comparison with a fresh tree at the end.

Let me know if you know how to ensure the PDT is in canonical form after updates, I don't have any more ideas for it  :(



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