C#: Filter away use-use steps from a node into itself

Author: hvitved

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

@@ -440,7 +440,8 @@ module LocalFlow {
       exists(CIL::ReadAccess readFrom, CIL::ReadAccess readTo |
         CilSsaImpl::hasAdjacentReadsExt(def, readFrom, readTo) and
         nodeTo = TCilExprNode(readTo) and
-        nodeFrom = TCilExprNode(readFrom)
+        nodeFrom = TCilExprNode(readFrom) and
+        nodeFrom != nodeTo
       )
       or
       // Flow into phi (read) node
@@ -483,7 +484,8 @@ module LocalFlow {
     or
     hasNodePath(any(LocalExprStepConfiguration x), nodeFrom, nodeTo)
     or
-    ThisFlow::adjacentThisRefs(nodeFrom, nodeTo)
+    ThisFlow::adjacentThisRefs(nodeFrom, nodeTo) and
+    nodeFrom != nodeTo
     or
     ThisFlow::adjacentThisRefs(nodeFrom.(PostUpdateNode).getPreUpdateNode(), nodeTo)
     or
@@ -541,7 +543,8 @@ predicate simpleLocalFlowStep(Node nodeFrom, Node nodeTo) {
   exists(SsaImpl::DefinitionExt def |
     LocalFlow::localSsaFlowStepUseUse(def, nodeFrom, nodeTo) and
     not FlowSummaryImpl::Private::Steps::prohibitsUseUseFlow(nodeFrom, _) and
-    not LocalFlow::usesInstanceField(def)
+    not LocalFlow::usesInstanceField(def) and
+    nodeFrom != nodeTo
   )
   or
   // Flow into phi (read)/uncertain SSA definition node from read
@@ -880,7 +883,8 @@ private module Cached {
   predicate localFlowStepImpl(Node nodeFrom, Node nodeTo) {
     LocalFlow::localFlowStepCommon(nodeFrom, nodeTo)
     or
-    LocalFlow::localSsaFlowStepUseUse(_, nodeFrom, nodeTo)
+    LocalFlow::localSsaFlowStepUseUse(_, nodeFrom, nodeTo) and
+    nodeFrom != nodeTo
     or
     exists(SsaImpl::DefinitionExt def |
       LocalFlow::localSsaFlowStep(def, nodeFrom, nodeTo) and