Index: include/llvm/Support/GenericDomTreeConstruction.h
===================================================================
--- include/llvm/Support/GenericDomTreeConstruction.h
+++ include/llvm/Support/GenericDomTreeConstruction.h
@@ -1191,6 +1191,14 @@
     });
     LLVM_DEBUG(dbgs() << "\n");
 
+    // Recalculate the DominatorTree when the number of updates
+    // exceeds a threshold, which always makes direct updating slower than
+    // recalculation. We select this threshold proportional to the
+    // size of the DominatorTree. The constant is selected
+    // by choosing the one with the best performance on some real-world inputs.
+    if (NumLegalized > DT.DomTreeNodes.size() / 75)
+      CalculateFromScratch(DT, &BUI);
+
     // If the DominatorTree was recalculated at some point, stop the batch
     // updates. Full recalculations ignore batch updates and look at the actual
     // CFG.