Data flow: Cache clearsContent

Author: hvitved

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

@@ -1258,7 +1258,7 @@ private module LocalFlowBigStep {
   private class FlowCheckNode extends Node {
     FlowCheckNode() {
       this instanceof CastNode or
-      clearsContent(this, _)
+      clearsContentCached(this, _)
     }
   }
 
@@ -3610,7 +3610,7 @@ private module FlowExploration {
       or
       exists(PartialPathNodeRev mid |
         revPartialPathStep(mid, node, sc1, sc2, ap, config) and
-        not clearsContent(node, ap.getHead()) and
+        not clearsContentCached(node, ap.getHead()) and
         not fullBarrier(node, config) and
         distSink(getNodeEnclosingCallable(node), config) <= config.explorationLimit()
       )
@@ -3624,7 +3624,7 @@ private module FlowExploration {
     exists(PartialPathNodeFwd mid |
       partialPathStep(mid, node, cc, sc1, sc2, ap, config) and
       not fullBarrier(node, config) and
-      not clearsContent(node, ap.getHead().getContent()) and
+      not clearsContentCached(node, ap.getHead().getContent()) and
       if node instanceof CastingNode
       then compatibleTypes(getNodeDataFlowType(node), ap.getType())
       else any()

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

@@ -256,6 +256,9 @@ private module Cached {
   cached
   predicate jumpStepCached(Node node1, Node node2) { jumpStep(node1, node2) }
 
+  cached
+  predicate clearsContentCached(Node n, Content c) { clearsContent(n, c) }
+
   /**
    * Gets a viable target for the lambda call `call`.
    *
@@ -1141,7 +1144,7 @@ abstract class AccessPathFront extends TAccessPathFront {
 
   TypedContent getHead() { this = TFrontHead(result) }
 
-  predicate isClearedAt(Node n) { clearsContent(n, getHead().getContent()) }
+  predicate isClearedAt(Node n) { clearsContentCached(n, getHead().getContent()) }
 }
 
 class AccessPathFrontNil extends AccessPathFront, TFrontNil {