cache hasLocationInfo and Node::toString in the dataflow stage

Author: erik-krogh

javascript/ql/src/semmle/javascript/dataflow/DataFlow.qll

@@ -149,6 +149,7 @@ module DataFlow {
      * For more information, see
      * [Locations](https://help.semmle.com/QL/learn-ql/ql/locations.html).
      */
+    cached
     predicate hasLocationInfo(
       string filepath, int startline, int startcolumn, int endline, int endcolumn
     ) {
@@ -171,6 +172,7 @@ module DataFlow {
     int getEndColumn() { hasLocationInfo(_, _, _, _, result) }
 
     /** Gets a textual representation of this element. */
+    cached
     string toString() { none() }
 
     /**
@@ -294,12 +296,13 @@ module DataFlow {
     override predicate hasLocationInfo(
       string filepath, int startline, int startcolumn, int endline, int endcolumn
     ) {
+      Stages::DataFlowStage::ref() and
       astNode.getLocation().hasLocationInfo(filepath, startline, startcolumn, endline, endcolumn)
     }
 
     override File getFile() { result = astNode.getFile() }
 
-    override string toString() { result = astNode.toString() }
+    override string toString() { Stages::DataFlowStage::ref() and result = astNode.toString() }
   }
 
   /**

javascript/ql/src/semmle/javascript/internal/CachedStages.qll

@@ -126,6 +126,10 @@ module Stages {
       exists(any(Expr e).getExceptionTarget())
       or
       exists(DataFlow::ssaDefinitionNode(_))
+      or
+      any(DataFlow::Node node).hasLocationInfo(_, _, _, _, _)
+      or
+      exists(any(DataFlow::Node node).toString())
     }
   }