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diff --git a/llvm/tools/llvm-xray/trie-node.h b/llvm/tools/llvm-xray/trie-node.h
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+//===- trie-node.h - XRay Call Stack Data Structure -----------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides a data structure and routines for working with call stacks
+// of instrumented functions.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TOOLS_LLVM_XRAY_STACK_TRIE_H
+#define LLVM_TOOLS_LLVM_XRAY_STACK_TRIE_H
+
+#include <forward_list>
+#include <numeric>
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallVector.h"
+
+/// A type to represent a trie of invocations. It is useful to construct a
+/// graph of these nodes from reading an XRay trace, such that each function
+/// call can be placed in a larger context.
+///
+/// The template parameter allows users of the template to attach their own
+/// data elements to each node in the invocation graph.
+template <typename AssociatedData> struct TrieNode {
+  /// The function ID.
+  int32_t FuncId;
+
+  /// The caller of this function.
+  TrieNode<AssociatedData> *Parent;
+
+  /// The callees from this function.
+  llvm::SmallVector<TrieNode<AssociatedData> *, 4> Callees;
+
+  /// Additional parameterized data on each node.
+  AssociatedData ExtraData;
+};
+
+/// Merges together two TrieNodes with like function ids, aggregating their
+/// callee lists and durations. The caller must provide storage where new merged
+/// nodes can be allocated in the form of a linked list.
+template <typename T, typename Callable>
+TrieNode<T> *
+mergeTrieNodes(const TrieNode<T> &Left, const TrieNode<T> &Right,
+               /*Non-deduced pointer type for nullptr compatibility*/
+               typename std::remove_reference<TrieNode<T> *>::type NewParent,
+               std::forward_list<TrieNode<T>> &NodeStore,
+               Callable &&MergeCallable) {
+  llvm::function_ref<T(const T &, const T &)> MergeFn(
+      std::forward<Callable>(MergeCallable));
+  assert(Left.FuncId == Right.FuncId);
+  NodeStore.push_front(TrieNode<T>{
+      Left.FuncId, NewParent, {}, MergeFn(Left.ExtraData, Right.ExtraData)});
+  auto I = NodeStore.begin();
+  auto *Node = &*I;
+
+  // Build a map of callees from the left side.
+  llvm::DenseMap<int32_t, TrieNode<T> *> LeftCalleesByFuncId;
+  for (auto *Callee : Left.Callees) {
+    LeftCalleesByFuncId[Callee->FuncId] = Callee;
+  }
+
+  // Iterate through the right side, either merging with the map values or
+  // directly adding to the Callees vector. The iteration also removes any
+  // merged values from the left side map.
+  // TODO: Unroll into iterative and explicit stack for efficiency.
+  for (auto *Callee : Right.Callees) {
+    auto iter = LeftCalleesByFuncId.find(Callee->FuncId);
+    if (iter != LeftCalleesByFuncId.end()) {
+      Node->Callees.push_back(
+          mergeTrieNodes(*(iter->second), *Callee, Node, NodeStore, MergeFn));
+      LeftCalleesByFuncId.erase(iter);
+    } else {
+      Node->Callees.push_back(Callee);
+    }
+  }
+
+  // Add any callees that weren't found in the right side.
+  for (auto MapPairIter : LeftCalleesByFuncId) {
+    Node->Callees.push_back(MapPairIter.second);
+  }
+
+  return Node;
+}
+
+#endif // LLVM_TOOLS_LLVM_XRAY_STACK_TRIE_H