[PATCH] D35571: [Dominators] Improve error checking in deleteEdge

[Daniel Berlin via llvm-commits]

This is O(N), so you may want to do it only #ifndef NDEBUG

On Tue, Jul 18, 2017 at 10:37 AM, Jakub Kuderski via Phabricator <
reviews at reviews.llvm.org> wrote:

> kuhar created this revision.
>
> This patch improves error detection in deleteEdge. It asserts that the
> edge doesn't exist in the CFG and that DomTree knew about this edge before.
>
>
> https://reviews.llvm.org/D35571
>
> Files:
>   include/llvm/Support/GenericDomTreeConstruction.h
>
>
> Index: include/llvm/Support/GenericDomTreeConstruction.h
> ===================================================================
> --- include/llvm/Support/GenericDomTreeConstruction.h
> +++ include/llvm/Support/GenericDomTreeConstruction.h
> @@ -569,11 +569,22 @@
>      assert(From && To && "Cannot disconnect nullptrs");
>      DEBUG(dbgs() << "Deleting edge " << BlockNamePrinter(From) << " -> "
>                   << BlockNamePrinter(To) << "\n");
> +
> +    // Ensure that the edge was in fact deleted from the CFG before
> informing
> +    // the DomTree about it.
> +    auto IsSuccessor = [](const NodePtr SuccCandidate, const NodePtr Of) {
> +      auto Successors = ChildrenGetter<NodePtr, IsPostDom>::Get(Of);
> +      return llvm::find(Successors, SuccCandidate) != Successors.end();
> +    };
> +    (void)IsSuccessor;
> +    assert(!IsSuccessor(To, From) && "Deleted edge still exists in the
> CFG!");
> +
>      const TreeNodePtr FromTN = DT.getNode(From);
>      // Deletion in an unreachable subtree -- nothing to do.
>      if (!FromTN) return;
>
>      const TreeNodePtr ToTN = DT.getNode(To);
> +    assert(ToTN && "To already unreachable -- there is no edge to
> delete");
>      const NodePtr NCDBlock = DT.findNearestCommonDominator(From, To);
>      const TreeNodePtr NCD = DT.getNode(NCDBlock);
>
>
>
>
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