diff --git a/clang/include/clang/Analysis/FlowSensitive/DataflowAnalysis.h b/clang/include/clang/Analysis/FlowSensitive/DataflowAnalysis.h
--- a/clang/include/clang/Analysis/FlowSensitive/DataflowAnalysis.h
+++ b/clang/include/clang/Analysis/FlowSensitive/DataflowAnalysis.h
@@ -106,8 +106,9 @@
 };
 
 /// Performs dataflow analysis and returns a mapping from basic block IDs to
-/// dataflow analysis states that model the respective basic blocks. Indices
-/// of the returned vector correspond to basic block IDs. Returns an error if
+/// dataflow analysis states that model the respective basic blocks. The
+/// returned vector, if any, will have the same size as the number of CFG
+/// blocks, with indices corresponding to basic block IDs. Returns an error if
 /// the dataflow analysis cannot be performed successfully.
 template <typename AnalysisT>
 llvm::Expected<std::vector<