C++: Add LoadChain and StoreChain nodes to handle reverse reads in dataflow

Author: MathiasVP

cpp/ql/src/semmle/code/cpp/ir/dataflow/internal/DataFlowPrivate.qll

@@ -180,46 +180,24 @@ private class ArrayContent extends Content, TArrayContent {
   override Type getType() { none() }
 }
 
-private predicate storeStepNoChi(Node node1, Content f, PostUpdateNode node2) {
-  exists(FieldAddressInstruction fa, StoreInstruction store |
-    store = node2.asInstruction() and
-    store.getDestinationAddress() = fa and
-    store.getSourceValue() = node1.asInstruction() and
-    f.(FieldContent).getField() = fa.getField()
-  )
-}
-
-private predicate storeStepChi(Node node1, Content f, PostUpdateNode node2) {
-  exists(FieldAddressInstruction fa, StoreInstruction store |
-    node1.asInstruction() = store and
-    store.getDestinationAddress() = fa and
-    node2.asInstruction().(ChiInstruction).getPartial() = store and
-    f.(FieldContent).getField() = fa.getField()
-  )
-}
-
 /**
  * Holds if data can flow from `node1` to `node2` via an assignment to `f`.
  * Thus, `node2` references an object with a field `f` that contains the
  * value of `node1`.
  */
-predicate storeStep(Node node1, Content f, PostUpdateNode node2) {
-  storeStepNoChi(node1, f, node2) or
-  storeStepChi(node1, f, node2)
+predicate storeStep(Node node1, Content f, StoreStepNode node2) {
+  node2.getStoredValue() = node1 and
+  f.(FieldContent).getField() = node2.getAField()
 }
 
 /**
  * Holds if data can flow from `node1` to `node2` via a read of `f`.
  * Thus, `node1` references an object with a field `f` whose value ends up in
  * `node2`.
  */
-predicate readStep(Node node1, Content f, Node node2) {
-  exists(FieldAddressInstruction fa, LoadInstruction load |
-    load.getSourceAddress() = fa and
-    node1.asInstruction() = load.getSourceValueOperand().getAnyDef() and
-    fa.getField() = f.(FieldContent).getField() and
-    load = node2.asInstruction()
-  )
+predicate readStep(Node node1, Content f, ReadStepNode node2) {
+  node2.getReadValue() = node1 and
+  f.(FieldContent).getField() = node2.getAField()
 }
 
 /**