[llvm] d575077 - [NFC][MachineOutliner] Rewrite setSuffixIndices to be iterative

[Jessica Paquette via llvm-commits]

Author: Jessica Paquette
Date: 2019-12-20T16:12:37-08:00
New Revision: d5750770eb96d6854c11726118d3215443d70643

URL: https://github.com/llvm/llvm-project/commit/d5750770eb96d6854c11726118d3215443d70643
DIFF: https://github.com/llvm/llvm-project/commit/d5750770eb96d6854c11726118d3215443d70643.diff

LOG: [NFC][MachineOutliner] Rewrite setSuffixIndices to be iterative

Having this function be recursive could use up way too much stack space.

Rewrite it as an iterative traversal in the tree instead to prevent this.

Fixes PR44344.

Added: 
    

Modified: 
    llvm/lib/CodeGen/MachineOutliner.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/MachineOutliner.cpp b/llvm/lib/CodeGen/MachineOutliner.cpp
index e3fc0f8aafdb..f742ac6b55c1 100644
--- a/llvm/lib/CodeGen/MachineOutliner.cpp
+++ b/llvm/lib/CodeGen/MachineOutliner.cpp
@@ -313,24 +313,31 @@ class SuffixTree {
   /// respective suffixes.
   ///
   /// \param[in] CurrNode The node currently being visited.
-  /// \param CurrNodeLen The concatenation of all node sizes from the root to
-  /// this node. Used to produce suffix indices.
-  void setSuffixIndices(SuffixTreeNode &CurrNode, unsigned CurrNodeLen) {
-
-    bool IsLeaf = CurrNode.Children.size() == 0 && !CurrNode.isRoot();
-
-    // Store the concatenation of lengths down from the root.
-    CurrNode.ConcatLen = CurrNodeLen;
-    // Traverse the tree depth-first.
-    for (auto &ChildPair : CurrNode.Children) {
-      assert(ChildPair.second && "Node had a null child!");
-      setSuffixIndices(*ChildPair.second,
-                       CurrNodeLen + ChildPair.second->size());
-    }
+  void setSuffixIndices() {
+    // List of nodes we need to visit along with the current length of the
+    // string.
+    std::vector<std::pair<SuffixTreeNode *, unsigned>> ToVisit;
+
+    // Current node being visited.
+    SuffixTreeNode *CurrNode = Root;
+
+    // Sum of the lengths of the nodes down the path to the current one.
+    unsigned CurrNodeLen = 0;
+    ToVisit.push_back({CurrNode, CurrNodeLen});
+    while (!ToVisit.empty()) {
+      std::tie(CurrNode, CurrNodeLen) = ToVisit.back();
+      ToVisit.pop_back();
+      CurrNode->ConcatLen = CurrNodeLen;
+      for (auto &ChildPair : CurrNode->Children) {
+        assert(ChildPair.second && "Node had a null child!");
+        ToVisit.push_back(
+            {ChildPair.second, CurrNodeLen + ChildPair.second->size()});
+      }
 
-    // Is this node a leaf? If it is, give it a suffix index.
-    if (IsLeaf)
-      CurrNode.SuffixIdx = Str.size() - CurrNodeLen;
+      // No children, so we are at the end of the string.
+      if (CurrNode->Children.size() == 0 && !CurrNode->isRoot())
+        CurrNode->SuffixIdx = Str.size() - CurrNodeLen;
+    }
   }
 
   /// Construct the suffix tree for the prefix of the input ending at
@@ -486,7 +493,7 @@ class SuffixTree {
 
     // Set the suffix indices of each leaf.
     assert(Root && "Root node can't be nullptr!");
-    setSuffixIndices(*Root, 0);
+    setSuffixIndices();
   }
 
   /// Iterator for finding all repeated substrings in the suffix tree.