update localFlow() to use fastTC

Author: chanel-y

python/ql/lib/semmle/python/dataflow/new/internal/DataFlowUtil.qll

@@ -20,9 +20,19 @@ predicate localFlowStep(Node nodeFrom, Node nodeTo) {
   FlowSummaryImpl::Private::Steps::summaryThroughStepValue(nodeFrom, nodeTo, _)
 }
 
+/**
+ * Holds if data flows from `source` to `sink` in one or more local
+ * (intra-procedural) steps.
+ */
+pragma[inline]
+private predicate localFlowPlus(Node source, Node sink) = fastTC(localFlowStep/2)(source, sink)
+
 /**
  * Holds if data flows from `source` to `sink` in zero or more local
  * (intra-procedural) steps.
  */
 pragma[inline]
-predicate localFlow(Node source, Node sink) { localFlowStep*(source, sink) }
+predicate localFlow(Node source, Node sink) {
+  localFlowPlus(source, sink) or 
+  source = sink
+}