C++: Use names that better match the AST dataflow library.

Author: MathiasVP

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

@@ -31,9 +31,19 @@ private class PrimaryArgumentNode extends ArgumentNode {
   override predicate argumentOf(DataFlowCall call, int pos) { op = call.getArgumentOperand(pos) }
 
   override string toString() {
-    result = "Argument " + op.(PositionalArgumentOperand).getIndex()
+    exists(Expr unconverted |
+      unconverted = op.getDef().getUnconvertedResultExpression() and
+      result = unconverted.toString()
+    )
     or
-    op instanceof ThisArgumentOperand and result = "This argument"
+    // Certain instructions don't map to an unconverted result expression. For these cases
+    // we fall back to a simpler naming scheme. This can happen in IR-generated constructors.
+    not exists(op.getDef().getUnconvertedResultExpression()) and
+    (
+      result = "Argument " + op.(PositionalArgumentOperand).getIndex()
+      or
+      op instanceof ThisArgumentOperand and result = "Argument this"
+    )
   }
 }
 
@@ -53,9 +63,16 @@ private class SideEffectArgumentNode extends ArgumentNode {
   }
 
   override string toString() {
-    if read.getIndex() = -1
-    then result = "This indirection"
-    else result = "Argument " + read.getIndex() + " indirection"
+    result = read.getArgumentDef().getUnconvertedResultExpression().toString() + " indirection"
+    or
+    // Some instructions don't map to an unconverted result expression. For these cases
+    // we fall back to a simpler naming scheme. This can happen in IR-generated constructors.
+    not exists(read.getArgumentDef().getUnconvertedResultExpression()) and
+    (
+      if read.getIndex() = -1
+      then result = "Argument this indirection"
+      else result = "Argument " + read.getIndex() + " indirection"
+    )
   }
 }