From a974c9ff48ea9c31bb888247832975b94941d41a Mon Sep 17 00:00:00 2001
From: Tom Hvitved <hvitved@github.com>
Date: Fri, 11 Oct 2024 19:35:54 +0200
Subject: [PATCH] wip

---
 .../codeql/dataflow/internal/DataFlowImpl.qll | 52 ++++++++++---------
 1 file changed, 27 insertions(+), 25 deletions(-)

diff --git a/shared/dataflow/codeql/dataflow/internal/DataFlowImpl.qll b/shared/dataflow/codeql/dataflow/internal/DataFlowImpl.qll
index 782a1349314c3..0ffc0c0f844c4 100644
--- a/shared/dataflow/codeql/dataflow/internal/DataFlowImpl.qll
+++ b/shared/dataflow/codeql/dataflow/internal/DataFlowImpl.qll
@@ -2606,6 +2606,23 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
           );
         }
 
+        /**
+         * A node where some checking is required, and hence the big-step relation
+         * is not allowed to step over.
+         */
+        additional class FlowCheckNode extends NodeEx {
+          FlowCheckNode() {
+            revFlow(this, _, _) and
+            (
+              castNode(this.asNode()) or
+              clearsContentCached(this.asNode(), _) or
+              expectsContentCached(this.asNode(), _) or
+              neverSkipInPathGraph(this.asNode()) or
+              Config::neverSkip(this.asNode())
+            )
+          }
+        }
+
         /**
          * Provides a big-step relation for local flow steps.
          *
@@ -2614,25 +2631,6 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
          * reachable in this stage.
          */
         additional module LocalFlowBigStep<LocalFlowBigStepInputSig Input> {
-          final private class NodeExFinal = NodeEx;
-
-          /**
-           * A node where some checking is required, and hence the big-step relation
-           * is not allowed to step over.
-           */
-          private class FlowCheckNode extends NodeExFinal {
-            FlowCheckNode() {
-              revFlow(this, _, _) and
-              (
-                castNode(this.asNode()) or
-                clearsContentCached(this.asNode(), _) or
-                expectsContentCached(this.asNode(), _) or
-                neverSkipInPathGraph(this.asNode()) or
-                Config::neverSkip(this.asNode())
-              )
-            }
-          }
-
           private predicate additionalLocalStateStep(
             NodeEx node1, FlowState state1, NodeEx node2, FlowState state2, DataFlowType t,
             LocalCallContext lcc, string label
@@ -4414,15 +4412,19 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
         private predicate smallStep = Stage3Param::BigStepInput::localStep/8;
 
         private predicate localStepCand(
-          NodeEx node1, FlowState state1, NodeEx node2, FlowState state2
+          NodeEx node1, FlowState state1, NodeEx node2, FlowState state2, boolean preservesValue
         ) {
-          PrevStage::revFlow(node1, state1, _) and
-          smallStep(node1, state1, node2, state2, _, _, _, _)
+          Stage5Param::localStep(node1, state1, _, _, _, _, _, _) and
+          smallStep(node1, state1, node2, state2, preservesValue, _, _, _)
           or
           exists(FlowState midState, NodeEx midNode |
-            localStepCand(node1, state1, midNode, midState) and
+            localStepCand(node1, state1, midNode, midState, preservesValue) and
             smallStep(midNode, midState, node2, state2, _, _, _, _) and
-            not Stage5Param::localStep(midNode, midState, _, _, _, _, _, _)
+            not (
+              Stage5Param::localStep(midNode, midState, _, _, _, _, _, _) and
+              Stage5Param::localStep(_, _, midNode, midState, _, _, _, _)
+            ) and
+            not midNode instanceof Stage5::FlowCheckNode
           )
         }
 
@@ -4439,7 +4441,7 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
           NodeEx node1, FlowState state1, NodeEx node2, FlowState state2, boolean preservesValue,
           DataFlowType t, LocalCallContext lcc, string label
         ) {
-          localStepCand(node1, state1, node2, state2) and
+          localStepCand(node1, state1, node2, state2, preservesValue) and
           Stage5Param::localStep(node1, state1, node2, state2, preservesValue, t, lcc, label) and
           PrevStage::revFlow(node1, pragma[only_bind_into](state1), _) and
           PrevStage::revFlow(node2, pragma[only_bind_into](state2), _)