[PATCH] D77341: [DomTree] Replace ChildrenGetter with GraphTraits over GraphDiff.

[Alina Sbirlea via Phabricator via cfe-commits]

asbirlea added inline comments.


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Comment at: llvm/include/llvm/Support/GenericDomTreeConstruction.h:185
+          std::make_pair(GDTmp, BB);
+      for (auto &Pair : children<GraphDiffBBPair>(GDNodePair)) {
+        const NodePtr Succ = Pair.second;
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kuhar wrote:
> Won't children infer the template parameter based on the passes value? I don't get why the template argument type is a pair where the second argument is a directed nodeptr, but the runtime value is always a plain nodeptr. Couldn't the second pair type also be directed for `GDNodePair`?
The directed nodeptr is the equivalent of a bool inside GraphDiff translating to what kind of children do you want; the second pair argument bears no info of that kind, only the actual NodePtr for which we desire the children.


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Comment at: llvm/include/llvm/Support/GenericDomTreeConstruction.h:186
+      for (auto &Pair : children<GraphDiffBBPair>(GDNodePair)) {
+        const NodePtr Succ = Pair.second;
         const auto SIT = NodeToInfo.find(Succ);
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kuhar wrote:
> kuhar wrote:
> > Could this new code be a hoisted into a helper function?
> Or alternatively, could the old `ChildrenGetter` be implemented with these 5 magic lines?
I think it looks much cleaner after the latest update, let me know what you think.


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Comment at: llvm/include/llvm/Support/GenericDomTreeConstruction.h:1543
+  // FIXME: Updated to use the PreViewCFG and behave the same as until now.
+  // This behavior is however incorrect; this actually needs the PostViewCFG.
+  GraphDiff<typename DomTreeT::NodePtr, DomTreeT::IsPostDominator> PreViewCFG(
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kuhar wrote:
> Does this care about the direction (pre- or post-) at all, or does it need some CFG view? Why is pre-view incorrect?
The purpose of this method was to update the DT assuming an additional list of updates (the argument given). In practice, the BUI argument is ignored in the `CalculateFromScratch` call below. Hence we need the additional changes to support this kind of updates inside `CalculateFromScratch` and the other methods.


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