diff --git a/bolt/include/bolt/Core/BinaryFunction.h b/bolt/include/bolt/Core/BinaryFunction.h
--- a/bolt/include/bolt/Core/BinaryFunction.h
+++ b/bolt/include/bolt/Core/BinaryFunction.h
@@ -710,8 +710,6 @@
   void releaseCFG() {
     for (BinaryBasicBlock *BB : BasicBlocks)
       BB->releaseCFG();
-    for (BinaryBasicBlock *BB : DeletedBasicBlocks)
-      BB->releaseCFG();
 
     clearList(CallSites);
     clearList(ColdCallSites);
diff --git a/bolt/lib/Core/BinaryFunction.cpp b/bolt/lib/Core/BinaryFunction.cpp
--- a/bolt/lib/Core/BinaryFunction.cpp
+++ b/bolt/lib/Core/BinaryFunction.cpp
@@ -348,7 +348,10 @@
     } else {
       assert(!isEntryPoint(*BB) && "all entry blocks must be valid");
       ++Count;
-      Bytes += BC.computeCodeSize(BB->begin(), BB->end());
+      if (BB->size()) {
+        std::unique_lock<std::shared_timed_mutex> Lock(BC.CtxMutex);
+        Bytes += BB->estimateSize();
+      }
     }
   }
   BasicBlocksLayout = std::move(NewLayout);
@@ -372,6 +375,9 @@
   if (Count > 0)
     recomputeLandingPads();
 
+  for (BinaryBasicBlock *BB : DeletedBasicBlocks)
+    BB->releaseCFG();
+
   return std::make_pair(Count, Bytes);
 }