[llvm] [DomTree] Avoid duplicate hash lookups in runDFS() (NFCI) (PR #96460)

[Jakub Kuderski via llvm-commits]

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@@ -180,15 +180,17 @@ struct SemiNCAInfo {
                   unsigned AttachToNum,
                   const NodeOrderMap *SuccOrder = nullptr) {
     assert(V);
-    SmallVector<NodePtr, 64> WorkList = {V};
+    SmallVector<std::pair<NodePtr, unsigned>, 64> WorkList = {{V, AttachToNum}};
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kuhar wrote:

This looks like a pretty large stack allocation (16B * 64 => 1kB?). Is this what we want?

https://github.com/llvm/llvm-project/pull/96460