diff --git a/llvm/lib/Transforms/Scalar/LoopSink.cpp b/llvm/lib/Transforms/Scalar/LoopSink.cpp
--- a/llvm/lib/Transforms/Scalar/LoopSink.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopSink.cpp
@@ -222,9 +222,11 @@
   // order. No need to stable sort as the block numbers are a total ordering.
   SmallVector<BasicBlock *, 2> SortedBBsToSinkInto;
   llvm::append_range(SortedBBsToSinkInto, BBsToSinkInto);
-  llvm::sort(SortedBBsToSinkInto, [&](BasicBlock *A, BasicBlock *B) {
-    return LoopBlockNumber.find(A)->second < LoopBlockNumber.find(B)->second;
-  });
+  if (SortedBBsToSinkInto.size() > 1) {
+    llvm::sort(SortedBBsToSinkInto, [&](BasicBlock *A, BasicBlock *B) {
+      return LoopBlockNumber.find(A)->second < LoopBlockNumber.find(B)->second;
+    });
+  }
 
   BasicBlock *MoveBB = *SortedBBsToSinkInto.begin();
   // FIXME: Optimize the efficiency for cloned value replacement. The current