Data flow: Cache simpleLocalFlowStep

Author: hvitved

csharp/ql/src/semmle/code/csharp/dataflow/internal/DataFlowImpl.qll

@@ -211,10 +211,7 @@ private predicate fullBarrier(Node node, Configuration config) {
  * Holds if data can flow in one local step from `node1` to `node2`.
  */
 private predicate localFlowStep(Node node1, Node node2, Configuration config) {
-  (
-    simpleLocalFlowStep(node1, node2) or
-    reverseStepThroughInputOutputAlias(node1, node2)
-  ) and
+  simpleLocalFlowStepExt(node1, node2) and
   not outBarrier(node1, config) and
   not inBarrier(node2, config) and
   not fullBarrier(node1, config) and

csharp/ql/src/semmle/code/csharp/dataflow/internal/DataFlowImplCommon.qll

@@ -689,8 +689,9 @@ private module Cached {
    * are aliases. A typical example is a function returning `this`, implementing a fluent
    * interface.
    */
-  cached
-  predicate reverseStepThroughInputOutputAlias(PostUpdateNode fromNode, PostUpdateNode toNode) {
+  private predicate reverseStepThroughInputOutputAlias(
+    PostUpdateNode fromNode, PostUpdateNode toNode
+  ) {
     exists(Node fromPre, Node toPre |
       fromPre = fromNode.getPreUpdateNode() and
       toPre = toNode.getPreUpdateNode()
@@ -707,6 +708,12 @@ private module Cached {
     )
   }
 
+  cached
+  predicate simpleLocalFlowStepExt(Node node1, Node node2) {
+    simpleLocalFlowStep(node1, node2) or
+    reverseStepThroughInputOutputAlias(node1, node2)
+  }
+
   /**
    * Holds if the call context `call` either improves virtual dispatch in
    * `callable` or if it allows us to prune unreachable nodes in `callable`.