[PATCH] D38541: [Dominators] Take fast path when applying <=1 updates

[Jakub Kuderski via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL314917: [Dominators] Take fast path when applying <=1 updates (authored by kuhar).

Changed prior to commit:
  https://reviews.llvm.org/D38541?vs=117670&id=117696#toc

Repository:
  rL LLVM

https://reviews.llvm.org/D38541

Files:
  llvm/trunk/include/llvm/Support/GenericDomTree.h
  llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h


Index: llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h
===================================================================
--- llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h
+++ llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h
@@ -1122,6 +1122,22 @@
   //~~
 
   static void ApplyUpdates(DomTreeT &DT, ArrayRef<UpdateT> Updates) {
+    const size_t NumUpdates = Updates.size();
+    if (NumUpdates == 0)
+      return;
+
+    // Take the fast path for a single update and avoid running the batch update
+    // machinery.
+    if (NumUpdates == 1) {
+      const auto &Update = Updates.front();
+      if (Update.getKind() == UpdateKind::Insert)
+        DT.insertEdge(Update.getFrom(), Update.getTo());
+      else
+        DT.deleteEdge(Update.getFrom(), Update.getTo());
+
+      return;
+    }
+
     BatchUpdateInfo BUI;
     LegalizeUpdates(Updates, BUI.Updates);
 
Index: llvm/trunk/include/llvm/Support/GenericDomTree.h
===================================================================
--- llvm/trunk/include/llvm/Support/GenericDomTree.h
+++ llvm/trunk/include/llvm/Support/GenericDomTree.h
@@ -522,7 +522,9 @@
   ///
   /// Batch updates should be generally faster when performing longer sequences
   /// of updates than calling insertEdge/deleteEdge manually multiple times, as
-  /// they can reorder the updates and remove redundant ones internally.
+  /// it can reorder the updates and remove redundant ones internally.
+  /// The batch updater is also able to detect sequences of zero and exactly one
+  /// update -- it's optimized to do less work in these cases.
   ///
   /// Note that for postdominators it automatically takes care of applying
   /// updates on reverse edges internally (so there's no need to swap the


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