C++: Remove unnecessary recursion through Node.toString.

cpp/ql/lib/semmle/code/cpp/dataflow/internal/FlowSummaryImpl.qll

@@ -201,7 +201,7 @@ module SourceSinkInterpretationInput implements
     string toString() {
       result = this.asElement().toString()
       or
-      result = this.asNode().toString()
+      result = this.asNode().toStringImpl()
       or
       result = this.asCall().toString()
     }

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

@@ -968,7 +968,7 @@ private class Node0 extends Node, TNode0 {
 
   override Location getLocationImpl() { result = node.getLocation() }
 
-  override string toStringImpl() { result = node.toString() }
+  override string toStringImpl() { result = node.toStringImpl() }
 
   override Type getType() { result = node.getType() }
 
@@ -1020,7 +1020,9 @@ class PostFieldUpdateNode extends PostUpdateNodeImpl {
 
   Field getUpdatedField() { result = this.getFieldAddress().getField() }
 
-  override string toStringImpl() { result = this.getPreUpdateNode() + " [post update]" }
+  override string toStringImpl() {
+    result = this.getPreUpdateNode().toStringImpl() + " [post update]"
+  }
 }
 
 /**
@@ -1187,9 +1189,7 @@ private class RawIndirectOperand0 extends Node, TRawIndirectOperand0 {
     else result instanceof UnknownLocation
   }
 
-  override string toStringImpl() {
-    result = stars(this) + operandNode(this.getOperand()).toStringImpl()
-  }
+  override string toStringImpl() { result = stars(this) + operandToString(this.getOperand()) }
 }
 
 /**
@@ -1232,7 +1232,7 @@ private class RawIndirectInstruction0 extends Node, TRawIndirectInstruction0 {
   }
 
   override string toStringImpl() {
-    result = stars(this) + instructionNode(this.getInstruction()).toStringImpl()
+    result = stars(this) + instructionToString(this.getInstruction())
   }
 }