[llvm] [ADT] Fuse the two post-mutation tree walks in ImutAVLFactory (PR #208907)

[Gábor Horváth via llvm-commits]

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@@ -460,11 +458,21 @@ class ImutAVLFactory {
     return createNode(newLeft, getValue(oldTree), newRight);
   }
 
-  void recoverNodes() {
-    for (unsigned i = 0, n = createdNodes.size(); i < n; ++i) {
-      TreeTy *N = createdNodes[i];
-      if (N->isMutable() && N->refCount == 0)
+  void recoverNodes(TreeTy *Result) {
+    // Mark Result's nodes immutable and reclaim the intermediates discarded
+    // during balancing, in one pass. Nodes are built bottom-up, so a node
+    // precedes its parents in createdNodes; visiting in reverse thus reaches
+    // each node only once its reference count is final. Unreferenced nodes are
+    // unreachable and destroyed; the rest belong to Result. Result is kept
+    // despite its zero count -- the caller has not taken ownership yet.
+    for (unsigned I = createdNodes.size(); I-- > 0;) {
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Xazax-hun wrote:

Good point, much cleaner now, thanks!

https://github.com/llvm/llvm-project/pull/208907