C++: Fix looping flow that goes from the output argument node and back into the function argument.

Author: MathiasVP

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/SsaInternals.qll

@@ -657,24 +657,16 @@ private predicate indirectConversionFlowStep(Node nFrom, Node nTo) {
  * So this predicate recurses back along conversions and `PointerArithmeticInstruction`s to find the
  * first use that has provides use-use flow, and uses that target as the target of the `nodeFrom`.
  */
-private predicate adjustForPointerArith(
-  DefOrUse defOrUse, Node nodeFrom, UseOrPhi use, boolean uncertain
-) {
-  nodeFrom = any(PostUpdateNode pun).getPreUpdateNode() and
-  exists(Node adjusted |
-    indirectConversionFlowStep*(adjusted, nodeFrom) and
-    nodeToDefOrUse(adjusted, defOrUse, uncertain) and
+private predicate adjustForPointerArith(PostUpdateNode pun, UseOrPhi use) {
+  exists(DefOrUse defOrUse, Node adjusted |
+    indirectConversionFlowStep*(adjusted, pun.getPreUpdateNode()) and
+    nodeToDefOrUse(adjusted, defOrUse, _) and
     adjacentDefRead(defOrUse, use)
   )
 }
 
 private predicate ssaFlowImpl(SsaDefOrUse defOrUse, Node nodeFrom, Node nodeTo, boolean uncertain) {
-  // `nodeFrom = any(PostUpdateNode pun).getPreUpdateNode()` is implied by adjustedForPointerArith.
   exists(UseOrPhi use |
-    adjustForPointerArith(defOrUse, nodeFrom, use, uncertain) and
-    useToNode(use, nodeTo)
-    or
-    not nodeFrom = any(PostUpdateNode pun).getPreUpdateNode() and
     nodeToDefOrUse(nodeFrom, defOrUse, uncertain) and
     adjacentDefRead(defOrUse, use) and
     useToNode(use, nodeTo) and
@@ -719,14 +711,19 @@ predicate ssaFlow(Node nodeFrom, Node nodeTo) {
   )
 }
 
+private predicate isArgumentOfCallable(DataFlowCall call, ArgumentNode arg) {
+  arg.argumentOf(call, _)
+}
+
+/** Holds if there is def-use or use-use flow from `pun` to `nodeTo`. */
 predicate postUpdateFlow(PostUpdateNode pun, Node nodeTo) {
-  exists(Node preUpdate, Node nFrom, boolean uncertain, SsaDefOrUse defOrUse |
+  exists(UseOrPhi use, Node preUpdate |
+    adjustForPointerArith(pun, use) and
+    useToNode(use, nodeTo) and
     preUpdate = pun.getPreUpdateNode() and
-    ssaFlowImpl(defOrUse, nFrom, nodeTo, uncertain)
-  |
-    if uncertain = true
-    then preUpdate = [nFrom, getAPriorDefinition(defOrUse)]
-    else preUpdate = nFrom
+    not exists(DataFlowCall call |
+      isArgumentOfCallable(call, preUpdate) and isArgumentOfCallable(call, nodeTo)
+    )
   )
 }