C#: Switch from ssaDefAssigns/ssaDefInitializesParam to ssaDefHasSource.

Author: aschackmull

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

@@ -506,7 +506,7 @@ module SsaFlow {
     result.(Impl::ExprPostUpdateNode).getExpr() =
       n.(PostUpdateNode).getPreUpdateNode().(ExprNode).getControlFlowNode()
     or
-    result.(Impl::ParameterNode).getParameter() = n.(ExplicitParameterNode).getSsaDefinition()
+    result.(Impl::WriteDefSourceNode).getDefinition() = n.(ExplicitParameterNode).getSsaDefinition()
   }
 
   predicate localFlowStep(Ssa::SourceVariable v, Node nodeFrom, Node nodeTo, boolean isUseStep) {

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

@@ -1023,6 +1023,12 @@ private module DataFlowIntegrationInput implements Impl::DataFlowIntegrationInpu
 
   Expr getARead(Definition def) { exists(getAReadAtNode(def, result)) }
 
+  predicate ssaDefHasSource(WriteDefinition def) {
+    // exclude flow directly from RHS to SSA definition, as we instead want to
+    // go from RHS to matching assignable definition, and from there to SSA definition
+    def instanceof Ssa::ImplicitParameterDefinition
+  }
+
   predicate ssaDefAssigns(WriteDefinition def, Expr value) {
     // exclude flow directly from RHS to SSA definition, as we instead want to
     // go from RHS to matching assingnable definition, and from there to SSA definition
@@ -1031,7 +1037,7 @@ private module DataFlowIntegrationInput implements Impl::DataFlowIntegrationInpu
 
   class Parameter = Ssa::ImplicitParameterDefinition;
 
-  predicate ssaDefInitializesParam(WriteDefinition def, Parameter p) { def = p }
+  predicate ssaDefInitializesParam(WriteDefinition def, Parameter p) { none() }
 
   /**
    * Allows for flow into uncertain defintions that are not call definitions,