C#: Remove the post update node restriction for argument and reverse step.

Author: michaelnebel

csharp/ql/lib/semmle/code/csharp/dataflow/internal/DataFlowPrivate.qll

@@ -1077,20 +1077,6 @@ private class FieldOrPropertyUsedInSource extends FieldOrProperty {
   }
 }
 
-/**
- * Hold if `e` has a type that allows for it to have a post-update node.
- */
-predicate exprMayHavePostUpdateNode(Expr e) {
-  exists(Type t | t = e.stripCasts().getType() |
-    t instanceof RefType and
-    not t instanceof NullType
-    or
-    t = any(TypeParameter tp | not tp.isValueType())
-    or
-    t.isRefLikeType()
-  )
-}
-
 /** A collection of cached types and predicates to be evaluated in the same stage. */
 cached
 private module Cached {
@@ -1137,15 +1123,12 @@ private module Cached {
       cfn.getAstNode().(ObjectCreation).hasInitializer()
     } or
     TExprPostUpdateNode(ControlFlow::Nodes::ExprNode cfn) {
-      (
-        cfn.getExpr() instanceof Argument
-        or
-        cfn =
-          LocalFlow::getPostUpdateReverseStep(any(ControlFlow::Nodes::ExprNode e |
-              exists(any(SourcePostUpdateNode p).getPreUpdateNode().asExprAtNode(e))
-            ))
-      ) and
-      exprMayHavePostUpdateNode(cfn.getExpr())
+      cfn.getExpr() instanceof Argument
+      or
+      cfn =
+        LocalFlow::getPostUpdateReverseStep(any(ControlFlow::Nodes::ExprNode e |
+            exists(any(SourcePostUpdateNode p).getPreUpdateNode().asExprAtNode(e))
+          ))
       or
       exists(Expr e | e = cfn.getExpr() |
         fieldOrPropertyStore(_, _, _, e, true)