[llvm] [Support][NFCI] Store DomTree children as linked list (PR #176409)

[Alexis Engelke via llvm-commits]

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@@ -60,25 +60,45 @@ template <class NodeT> class DomTreeNodeBase {
   NodeT *TheBB;
   DomTreeNodeBase *IDom;
   unsigned Level;
-  SmallVector<DomTreeNodeBase *, 4> Children;
+  DomTreeNodeBase *FirstChild = nullptr;
+  DomTreeNodeBase *Sibling = nullptr;
+  DomTreeNodeBase **AppendPtr = &FirstChild;
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aengelke wrote:

I still see no benefit from splitting the class. GenericDomTree is already separated from GenericDomTreeConstruction. IMO, further subclasses increase code complexity (ilist is a particularly extreme example for this, I remember spending many hours reading and debugging ilist code, which I found pretty convoluted). There is no other user that would reuse the code and DomTreeNodeBase is/remains pretty close to a bare bone tree node implementation.

Should you consider the existing DomTree testing as truly insufficient, I can add a case to GenericDomTreeTest that specifically exercises addNode/removeNode.


https://github.com/llvm/llvm-project/pull/176409