C++: Add qldoc (and remove predicate that wasn't needed).

Author: MathiasVP

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

@@ -241,7 +241,7 @@ private predicate instrToFieldNodeStoreStepNoChi(
     not exists(ChiInstruction chi | chi.getPartial() = store) and
     post.getPreUpdateNode() = getFieldNodeForFieldInstruction(store.getDestinationAddress()) and
     store.getSourceValueOperand() = node1.asOperand() and
-    f.getADirectField() = post.getField()
+    f.getADirectField() = post.getPreUpdateNode().getField()
   )
 }
 
@@ -262,7 +262,7 @@ private predicate instrToFieldNodeStoreStepChi(
     chi.getPartialOperand() = operand and
     store = operand.getDef() and
     post.getPreUpdateNode() = getFieldNodeForFieldInstruction(store.getDestinationAddress()) and
-    f.getADirectField() = post.getField()
+    f.getADirectField() = post.getPreUpdateNode().getField()
   )
 }
 
@@ -278,7 +278,7 @@ private predicate callableWithoutDefinitionStoreStep(
     post = node2.getPartialDefinition() and
     node1.asInstruction() = write and
     post.getPreUpdateNode() = getFieldNodeForFieldInstruction(write.getDestinationAddress()) and
-    f.getADirectField() = post.getField() and
+    f.getADirectField() = post.getPreUpdateNode().getField() and
     callable = write.getPrimaryInstruction().(CallInstruction).getStaticCallTarget() and
     not callable.hasDefinition()
   )

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

@@ -283,8 +283,6 @@ class PostUpdateFieldNode extends PartialDefinition {
   override Expr getDefinedExpr() {
     result = node.getFieldInstruction().getObjectAddress().getUnconvertedResultExpression()
   }
-
-  Field getField() { result = node.getField() }
 }
 
 /**
@@ -450,10 +448,13 @@ abstract class PartialDefinition extends TPartialDefinition {
 
   PartialDefinition() { this = MkPartialDefinition(node) }
 
+  /** Gets the node before the state update. */
   abstract Node getPreUpdateNode();
 
+  /** Gets the expression that is partially defined by this node. */
   abstract Expr getDefinedExpr();
 
+  /** Gets a string representation of this partial definition. */
   string toString() { result = node.toString() + " [partial definition]" }
 }
 
@@ -480,6 +481,7 @@ class PartialDefinitionNode extends PostUpdateNode, TPartialDefinitionNode {
 
   override Node getPreUpdateNode() { result = pd.getPreUpdateNode() }
 
+  /** Gets the `PartialDefinition` associated with this node. */
   PartialDefinition getPartialDefinition() { result = pd }
 
   override string toString() { result = getPreUpdateNode().toString() + " [post update]" }