[llvm] [MachineOutliner] Leaf Descendants (PR #90275)

[Kyungwoo Lee via llvm-commits]

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@@ -105,6 +114,68 @@ void SuffixTree::setSuffixIndices() {
   }
 }
 
+void SuffixTree::setLeafNodes() {
+  // A stack that keeps track of nodes to visit for post-order DFS traversal.
+  std::stack<SuffixTreeNode *> ToVisit;
+  ToVisit.push(Root);
+
+  // This keeps track of the index of the next leaf node to be added to
+  // the LeafNodes vector of the suffix tree.
+  unsigned LeafCounter = 0;
+
+  // This keeps track of nodes whose children have been added to the stack
+  // during the post-order depth-first traversal of the tree.
+  llvm::SmallPtrSet<SuffixTreeInternalNode *, 32> ChildrenAddedToStack;
+
+  // Traverse the tree in post-order.
+  while (!ToVisit.empty()) {
+    SuffixTreeNode *CurrNode = ToVisit.top();
+    ToVisit.pop();
+    if (auto *CurrInternalNode = dyn_cast<SuffixTreeInternalNode>(CurrNode)) {
+      // The current node is an internal node.
+      if (ChildrenAddedToStack.find(CurrInternalNode) !=
+          ChildrenAddedToStack.end()) {
+        // If the children of the current node has been added to the stack,
+        // then this is the second time we visit this node and at this point,
+        // all of its children have already been processed. Now, we can
+        // set its LeftLeafIdx and RightLeafIdx;
+        auto it = CurrInternalNode->Children.begin();
+        if (it != CurrInternalNode->Children.end()) {
+          // Get the first child to use its RightLeafIdx. The RightLeafIdx is
+          // used as the first child is the initial one added to the stack, so
+          // it's the last one to be processed. This implies that the leaf
+          // descendants of the first child are assigned the largest index
+          // numbers.
+          CurrNode->setRightLeafIdx(it->second->getRightLeafIdx());
+          // get the last child to use its LeftLeafIdx.
+          while (std::next(it) != CurrInternalNode->Children.end())
+            it = std::next(it);
+          CurrNode->setLeftLeafIdx(it->second->getLeftLeafIdx());
+          assert(CurrNode->getLeftLeafIdx() <= CurrNode->getRightLeafIdx() &&
+                 "LeftLeafIdx should not be larger than RightLeafIdx");
+        }
+      } else {
+        // This is the first time we visit this node. This means that its
+        // children have not been added to the stack yet. Hence, we will add
+        // the current node back to the stack and add its children to the
+        // stack for processing.
+        ToVisit.push(CurrNode);
+        for (auto &ChildPair : CurrInternalNode->Children)
+          ToVisit.push(ChildPair.second);
+        ChildrenAddedToStack.insert(CurrInternalNode);
+      }
+    } else {
+      // The current node is a leaf node.
+      // We can simplyset its LeftLeafIdx and RightLeafIdx.
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kyulee-com wrote:

simplyset -> simply set

https://github.com/llvm/llvm-project/pull/90275