[llvm] [Support][NFC] Use DomTreeBase methods in SemiNCA (PR #101059)

[Nikita Popov via llvm-commits]

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@@ -586,7 +586,8 @@ struct SemiNCAInfo {
     // Loop over all of the discovered blocks in the function...
     for (NodePtr W : llvm::drop_begin(NumToNode)) {
       // Don't replace this with 'count', the insertion side effect is important
-      if (DT.DomTreeNodes[W]) continue;  // Haven't calculated this node yet?
+      if (DT.getNode(W))
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nikic wrote:

I don't really see how the insertion side effect here could be important. And the original commit https://github.com/llvm/llvm-project/commit/daef1bcfbbf3718411a4a7b97cd4c690122823b9 doesn't say either.

I think there might have been some confusion here and what's actually important is not the insertion side effect, but that both `DT.DomTreeNodes.contains(W)` *and* `DT.DomTreeNodes[W] != nullptr`, rather than just the former.

https://github.com/llvm/llvm-project/pull/101059