[llvm] r314801 - [Dominators] Add DFS number verification

Juergen Ributzka via llvm-commits llvm-commits at lists.llvm.org
Tue Oct 3 13:42:38 PDT 2017


I don't know if this is reproducible on Linux, but the file that is failing
is common code in compiler-rt (sanitizer_libc.cc.o).

On Tue, Oct 3, 2017 at 1:32 PM, Jakub (Kuba) Kuderski <
kubakuderski at gmail.com> wrote:

> Hi Juergen,
>
> It seems like the patch caught some invalid DominatorTrees :).
>
> I'm now investigating a failure in LoopRotation happening in
> test/Transforms/ArgumentPromotion/pr3085.ll with expensive checks
> enabled, but I don't know if that's related.
> I looked and the buildbot's output and it seems to fail on OSX -- do you
> know if it's reproducible on x86_64 linux?
>
> Best,
> Jakub
>
> On Tue, Oct 3, 2017 at 4:26 PM, Juergen Ributzka <juergen at ributzka.de>
> wrote:
>
>> Hi Jakub,
>>
>> I think this broke one of our jobs on Green Dragon:
>> http://green.lab.llvm.org/green/job/clang-stage1-cmake-RA-
>> expensive/8568/consoleFull
>>
>> Could you please take a look?
>>
>> Thanks
>>
>> Cheers,
>> Juergen
>>
>> On Tue, Oct 3, 2017 at 7:33 AM, Jakub Kuderski via llvm-commits <
>> llvm-commits at lists.llvm.org> wrote:
>>
>>> Author: kuhar
>>> Date: Tue Oct  3 07:33:41 2017
>>> New Revision: 314801
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=314801&view=rev
>>> Log:
>>> [Dominators] Add DFS number verification
>>>
>>> Summary:
>>> This patch teaches the DominatorTree verifier to check DFS In/Out
>>> numbers which are used to answer dominance queries.
>>> DFS number verification is done in O(nlogn), so it shouldn't add much
>>> overhead on top of the O(n^3) sibling property verification.
>>> This check should detect errors like the one spotted in PR34466 and
>>> related bug reports.
>>>
>>> The patch also cleans up the DFS calculation a bit, as all constructed
>>> trees should have a single root now.
>>>
>>> I see 2 new test failures when running check-all after this change:
>>>
>>> ```
>>> Failing Tests (2):
>>>     Polly :: Isl/CodeGen/OpenMP/reference-a
>>> rgument-from-non-affine-region.ll
>>>     Polly :: Isl/CodeGen/OpenMP/two-paralle
>>> l-loops-reference-outer-indvar.ll
>>>
>>> ```
>>> which seem to happen just after `Create LLVM-IR from SCoPs` -- I XFAILed
>>> them in r314800.
>>>
>>> Reviewers: dberlin, grosser, davide, zhendongsu, bollu
>>>
>>> Reviewed By: dberlin
>>>
>>> Subscribers: nandini12396, bollu, Meinersbur, brzycki, llvm-commits
>>>
>>> Differential Revision: https://reviews.llvm.org/D38331
>>>
>>> Modified:
>>>     llvm/trunk/include/llvm/Support/GenericDomTree.h
>>>     llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h
>>>
>>> Modified: llvm/trunk/include/llvm/Support/GenericDomTree.h
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/
>>> Support/GenericDomTree.h?rev=314801&r1=314800&r2=314801&view=diff
>>> ============================================================
>>> ==================
>>> --- llvm/trunk/include/llvm/Support/GenericDomTree.h (original)
>>> +++ llvm/trunk/include/llvm/Support/GenericDomTree.h Tue Oct  3
>>> 07:33:41 2017
>>> @@ -702,28 +702,25 @@ public:
>>>        return;
>>>      }
>>>
>>> -    unsigned DFSNum = 0;
>>> -
>>>      SmallVector<std::pair<const DomTreeNodeBase<NodeT> *,
>>>                            typename DomTreeNodeBase<NodeT>::const_
>>> iterator>,
>>>                  32> WorkStack;
>>>
>>>      const DomTreeNodeBase<NodeT> *ThisRoot = getRootNode();
>>> -
>>> +    assert((!Parent || ThisRoot) && "Empty constructed DomTree");
>>>      if (!ThisRoot)
>>>        return;
>>>
>>> -    // Even in the case of multiple exits that form the post dominator
>>> root
>>> -    // nodes, do not iterate over all exits, but start from the virtual
>>> root
>>> -    // node. Otherwise bbs, that are not post dominated by any exit but
>>> by the
>>> -    // virtual root node, will never be assigned a DFS number.
>>> -    WorkStack.push_back(std::make_pair(ThisRoot, ThisRoot->begin()));
>>> +    // Both dominators and postdominators have a single root node. In
>>> the case
>>> +    // case of PostDominatorTree, this node is a virtual root.
>>> +    WorkStack.push_back({ThisRoot, ThisRoot->begin()});
>>> +
>>> +    unsigned DFSNum = 0;
>>>      ThisRoot->DFSNumIn = DFSNum++;
>>>
>>>      while (!WorkStack.empty()) {
>>>        const DomTreeNodeBase<NodeT> *Node = WorkStack.back().first;
>>> -      typename DomTreeNodeBase<NodeT>::const_iterator ChildIt =
>>> -          WorkStack.back().second;
>>> +      const auto ChildIt = WorkStack.back().second;
>>>
>>>        // If we visited all of the children of this node, "recurse" back
>>> up the
>>>        // stack setting the DFOutNum.
>>> @@ -735,7 +732,7 @@ public:
>>>          const DomTreeNodeBase<NodeT> *Child = *ChildIt;
>>>          ++WorkStack.back().second;
>>>
>>> -        WorkStack.push_back(std::make_pair(Child, Child->begin()));
>>> +        WorkStack.push_back({Child, Child->begin()});
>>>          Child->DFSNumIn = DFSNum++;
>>>        }
>>>      }
>>>
>>> Modified: llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/
>>> Support/GenericDomTreeConstruction.h?rev=314801&r1=314800&r2
>>> =314801&view=diff
>>> ============================================================
>>> ==================
>>> --- llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h
>>> (original)
>>> +++ llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h Tue
>>> Oct  3 07:33:41 2017
>>> @@ -1349,6 +1349,102 @@ struct SemiNCAInfo {
>>>      return true;
>>>    }
>>>
>>> +  // Check if the computed DFS numbers are correct. Note that DFS info
>>> may not
>>> +  // be valid, and when that is the case, we don't verify the numbers.
>>> +  static bool VerifyDFSNumbers(const DomTreeT &DT) {
>>> +    if (!DT.DFSInfoValid || !DT.Parent)
>>> +      return true;
>>> +
>>> +    const NodePtr RootBB = IsPostDom ? nullptr : DT.getRoots()[0];
>>> +    const TreeNodePtr Root = DT.getNode(RootBB);
>>> +
>>> +    auto PrintNodeAndDFSNums = [](const TreeNodePtr TN) {
>>> +      errs() << BlockNamePrinter(TN) << " {" << TN->getDFSNumIn() << ",
>>> "
>>> +             << TN->getDFSNumOut() << '}';
>>> +    };
>>> +
>>> +    // Verify the root's DFS In number. Although DFS numbering would
>>> also work
>>> +    // if we started from some other value, we assume 0-based numbering.
>>> +    if (Root->getDFSNumIn() != 0) {
>>> +      errs() << "DFSIn number for the tree root is not:\n\t";
>>> +      PrintNodeAndDFSNums(Root);
>>> +      errs() << '\n';
>>> +      errs().flush();
>>> +      return false;
>>> +    }
>>> +
>>> +    // For each tree node verify if children's DFS numbers cover their
>>> parent's
>>> +    // DFS numbers with no gaps.
>>> +    for (const auto &NodeToTN : DT.DomTreeNodes) {
>>> +      const TreeNodePtr Node = NodeToTN.second.get();
>>> +
>>> +      // Handle tree leaves.
>>> +      if (Node->getChildren().empty()) {
>>> +        if (Node->getDFSNumIn() + 1 != Node->getDFSNumOut()) {
>>> +          errs() << "Tree leaf should have DFSOut = DFSIn + 1:\n\t";
>>> +          PrintNodeAndDFSNums(Node);
>>> +          errs() << '\n';
>>> +          errs().flush();
>>> +          return false;
>>> +        }
>>> +
>>> +        continue;
>>> +      }
>>> +
>>> +      // Make a copy and sort it such that it is possible to check if
>>> there are
>>> +      // no gaps between DFS numbers of adjacent children.
>>> +      SmallVector<TreeNodePtr, 8> Children(Node->begin(), Node->end());
>>> +      std::sort(Children.begin(), Children.end(),
>>> +                [](const TreeNodePtr Ch1, const TreeNodePtr Ch2) {
>>> +                  return Ch1->getDFSNumIn() < Ch2->getDFSNumIn();
>>> +                });
>>> +
>>> +      auto PrintChildrenError = [Node, &Children, PrintNodeAndDFSNums](
>>> +          const TreeNodePtr FirstCh, const TreeNodePtr SecondCh =
>>> nullptr) {
>>> +        assert(FirstCh);
>>> +
>>> +        errs() << "Incorrect DFS numbers for:\n\tParent ";
>>> +        PrintNodeAndDFSNums(Node);
>>> +
>>> +        errs() << "\n\tChild ";
>>> +        PrintNodeAndDFSNums(FirstCh);
>>> +
>>> +        if (SecondCh) {
>>> +          errs() << "\n\tSecond child ";
>>> +          PrintNodeAndDFSNums(SecondCh);
>>> +        }
>>> +
>>> +        errs() << "\nAll children: ";
>>> +        for (const TreeNodePtr Ch : Children) {
>>> +          PrintNodeAndDFSNums(Ch);
>>> +          errs() << ", ";
>>> +        }
>>> +
>>> +        errs() << '\n';
>>> +        errs().flush();
>>> +      };
>>> +
>>> +      if (Children.front()->getDFSNumIn() != Node->getDFSNumIn() + 1) {
>>> +        PrintChildrenError(Children.front());
>>> +        return false;
>>> +      }
>>> +
>>> +      if (Children.back()->getDFSNumOut() + 1 != Node->getDFSNumOut())
>>> {
>>> +        PrintChildrenError(Children.back());
>>> +        return false;
>>> +      }
>>> +
>>> +      for (size_t i = 0, e = Children.size() - 1; i != e; ++i) {
>>> +        if (Children[i]->getDFSNumOut() + 1 != Children[i +
>>> 1]->getDFSNumIn()) {
>>> +          PrintChildrenError(Children[i], Children[i + 1]);
>>> +          return false;
>>> +        }
>>> +      }
>>> +    }
>>> +
>>> +    return true;
>>> +  }
>>> +
>>>    // Checks if for every edge From -> To in the graph
>>>    //     NCD(From, To) == IDom(To) or To.
>>>    bool verifyNCD(const DomTreeT &DT) {
>>> @@ -1521,7 +1617,8 @@ bool Verify(const DomTreeT &DT) {
>>>    SemiNCAInfo<DomTreeT> SNCA(nullptr);
>>>    return SNCA.verifyRoots(DT) && SNCA.verifyReachability(DT) &&
>>>           SNCA.VerifyLevels(DT) && SNCA.verifyNCD(DT) &&
>>> -         SNCA.verifyParentProperty(DT) && SNCA.verifySiblingProperty(DT)
>>> ;
>>> +         SNCA.verifyParentProperty(DT) &&
>>> SNCA.verifySiblingProperty(DT) &&
>>> +         SNCA.VerifyDFSNumbers(DT);
>>>  }
>>>
>>>  }  // namespace DomTreeBuilder
>>>
>>>
>>> _______________________________________________
>>> llvm-commits mailing list
>>> llvm-commits at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>>>
>>
>>
>
>
> --
> Jakub Kuderski
>
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