diff --git a/clang-tools-extra/clangd/index/dex/Iterator.cpp b/clang-tools-extra/clangd/index/dex/Iterator.cpp
--- a/clang-tools-extra/clangd/index/dex/Iterator.cpp
+++ b/clang-tools-extra/clangd/index/dex/Iterator.cpp
@@ -104,11 +104,19 @@
         // In this case, just terminate the process.
         if (ReachedEnd)
           return;
+        // Cache the result so that peek() is not called again as it may be
+        // quite expensive in AND with large subtrees.
+        auto Candidate = Child->peek();
         // If any child goes beyond given ID (i.e. ID is not the common item),
         // all children should be advanced to the next common item.
-        if (Child->peek() > SyncID) {
-          SyncID = Child->peek();
+        if (Candidate > SyncID) {
+          SyncID = Candidate;
           NeedsAdvance = true;
+          // Reset and try to sync again. Sync starts with the first child as
+          // this is the cheapest (smallest size estimate). This way advanceTo
+          // is called on the large posting lists once the sync point is very
+          // likely.
+          break;
         }
       }
     } while (NeedsAdvance);