Update comment

Author: philass

mlir/include/mlir/Analysis/DataFlowFramework.h

@@ -538,6 +538,11 @@ class AnalysisState {
   friend class DataFlowSolver;
 };
 
+//===----------------------------------------------------------------------===//
+// DataFlowSolver definition
+//===----------------------------------------------------------------------===//
+// This is method is defined outside `DataFlowSolver` and after `AnalysisState`
+// to prevent issues around `AnalysisState` being used before it is defined.
 template <typename AnchorT>
 void DataFlowSolver::eraseState(AnchorT anchor) {
   LatticeAnchor latticeAnchor(anchor);