[PATCH] D56284: [UnrollRuntime] Fix domTree failure in multiexit unrolling

[Jakub Kuderski via Phabricator via llvm-commits]

kuhar added a comment.

In D56284#1348747 <https://reviews.llvm.org/D56284#1348747>, @anna wrote:

> I've got a naive question about the DTU: Does the automatic updater handle the ImmediateDominator "automatically" for the remaining nodes in the dom tree once identify that one of the nodes in the DT has a change in IDom?


Exactly. Given a set of CFG updates, if figures out how to change the DomTree and PostDomTree such that they match the CFG.

> This will drastically help with #2 because what I have as a local fix using the old DT is something like this:
> 
>   +   if (DT) {
>   +    // Check the dom children of each block in loop and if it is outside the
>   +    // current loop, update it to the preheader.
>   +    for (auto *BB: L->blocks()) {
>   +      auto *DomNodeBB = DT->getNode(BB);
>   +      for (auto *DomChild: DomNodeBB->getChildren()) {
>   +        if (!L->contains(LI->getLoopFor(DomChild->getBlock()))) {
>   +          DT->changeImmediateDominator(DomChild, DT->getNode(PreHeader));
>   +        }    
>   +      }    
>   +    }
>   +   }
> 
> 
> This is a more general fix using the old DT to handle the non-immediate successors of an exit block in the loop.

Doesn't this loop have to be run until you reach a fixpoint?


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  rL LLVM

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https://reviews.llvm.org/D56284