C#: Address some review comments.

Author: aschackmull

csharp/ql/lib/semmle/code/csharp/dataflow/SSA.qll

@@ -183,14 +183,7 @@ module Ssa {
    * Subsequent reads can be found by following the steps defined by
    * `AssignableRead.getANextRead()`.
    */
-  AssignableRead ssaGetAFirstUse(SsaDefinition def) {
-    exists(ControlFlowNode cfn |
-      SsaImpl::firstReadSameVar(def, cfn) and
-      result.getControlFlowNode() = cfn
-    )
-  }
-
-  predicate isLiveOutRefParameterDefinition = SsaImpl::isLiveOutRefParameterDefinition/2;
+  AssignableRead ssaGetAFirstUse(SsaDefinition def) { SsaImpl::firstReadSameVar(def, result) }
 
   /**
    * DEPRECATED: Use `SsaDefinition` instead.
@@ -350,7 +343,7 @@ module Ssa {
      * `AssignableRead.getANextRead()`.
      */
     deprecated final AssignableRead getAFirstReadAtNode(ControlFlowNode cfn) {
-      SsaImpl::firstReadSameVar(this, cfn) and
+      SsaImpl::firstReadSameVar(this, result) and
       result.getControlFlowNode() = cfn
     }
 
@@ -416,7 +409,7 @@ module Ssa {
     }
 
     /**
-     * DEPRECATED: Use `isLiveOutRefParameterDefinition(SsaDefinition, Parameter)` instead.
+     * DEPRECATED.
      *
      * Holds if this SSA definition assigns to `out`/`ref` parameter `p`, and the
      * parameter may remain unchanged throughout the rest of the enclosing callable.

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

@@ -1605,7 +1605,7 @@ private module ReturnNodes {
 
     OutRefReturnNode() {
       exists(Parameter p |
-        Ssa::isLiveOutRefParameterDefinition(this.getDefinition(), p) and
+        SsaImpl::isLiveOutRefParameterDefinition(this.getDefinition(), p) and
         kind.getPosition() = p.getPosition()
       |
         p.isOut() and kind instanceof OutReturnKind

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

@@ -854,12 +854,14 @@ private module Cached {
   }
 
   /**
-   * Holds if the value defined at SSA definition `def` can reach a read at `cfn`,
+   * Holds if the value defined at SSA definition `def` can reach a read `read`,
    * without passing through any other read.
    */
   cached
-  predicate firstReadSameVar(Definition def, ControlFlowNode cfn) {
-    exists(BasicBlock bb, int i | Impl::firstUse(def, bb, i, true) and cfn = bb.getNode(i))
+  predicate firstReadSameVar(Definition def, AssignableRead read) {
+    exists(BasicBlock bb, int i |
+      Impl::firstUse(def, bb, i, true) and read.getControlFlowNode() = bb.getNode(i)
+    )
   }
 
   /**

csharp/ql/test/library-tests/dataflow/callablereturnsarg/Common.qll

@@ -1,11 +1,12 @@
 import csharp
 private import semmle.code.csharp.controlflow.Guards
+private import semmle.code.csharp.dataflow.internal.SsaImpl as SsaImpl
 
 private predicate outRefDef(DataFlow::ExprNode ne, int outRef) {
   exists(SsaExplicitWrite def, Parameter outRefParameter |
     outRefParameter.isOutOrRef() and
     ne.getExpr() = def.getValue() and
-    Ssa::isLiveOutRefParameterDefinition(def, outRefParameter) and
+    SsaImpl::isLiveOutRefParameterDefinition(def, outRefParameter) and
     outRef = outRefParameter.getPosition()
   )
 }

csharp/ql/test/library-tests/dataflow/ssa/IsLiveOutRefParameterDefinition.ql

@@ -1,7 +1,8 @@
 import csharp
+private import semmle.code.csharp.dataflow.internal.SsaImpl as SsaImpl
 
 from Ssa::SourceVariable v, SsaDefinition def
 where
   v = def.getSourceVariable() and
-  Ssa::isLiveOutRefParameterDefinition(def, _)
+  SsaImpl::isLiveOutRefParameterDefinition(def, _)
 select v, def