C#: Fix a few minor performance regressions

csharp/ql/src/API Abuse/DisposeNotCalledOnException.ql

@@ -49,18 +49,28 @@ predicate isTriedAgainstException(ControlFlowElement cfe, ExceptionClass ec) {
   )
 }
 
+private class DisposeCall extends MethodCall {
+  DisposeCall() { this.getTarget() instanceof DisposeMethod }
+}
+
+private predicate reachesDisposeCall(DisposeCall disposeCall, DataFlow::Node node) {
+  DataFlow::localFlowStep(node, DataFlow::exprNode(disposeCall.getQualifier()))
+  or
+  exists(DataFlow::Node mid | reachesDisposeCall(disposeCall, mid) |
+    DataFlow::localFlowStep(node, mid)
+  )
+}
+
 /**
  * Holds if `disposeCall` disposes the object created by `disposableCreation`.
  */
-predicate disposeReachableFromDisposableCreation(MethodCall disposeCall, Expr disposableCreation) {
+predicate disposeReachableFromDisposableCreation(DisposeCall disposeCall, Expr disposableCreation) {
   // The qualifier of the Dispose call flows from something that introduced a disposable into scope
   (
     disposableCreation instanceof LocalScopeDisposableCreation or
     disposableCreation instanceof MethodCall
   ) and
-  DataFlow::localFlowStep+(DataFlow::exprNode(disposableCreation),
-    DataFlow::exprNode(disposeCall.getQualifier())) and
-  disposeCall.getTarget() instanceof DisposeMethod
+  reachesDisposeCall(disposeCall, DataFlow::exprNode(disposableCreation))
 }
 
 class MethodCallThatMayThrow extends MethodCall {
@@ -73,7 +83,7 @@ ControlFlowElement getACatchOrFinallyClauseChild() {
   result = getACatchOrFinallyClauseChild().getAChild()
 }
 
-from MethodCall disposeCall, Expr disposableCreation, MethodCallThatMayThrow callThatThrows
+from DisposeCall disposeCall, Expr disposableCreation, MethodCallThatMayThrow callThatThrows
 where
   disposeReachableFromDisposableCreation(disposeCall, disposableCreation) and
   // The dispose call is not, itself, within a dispose method.

csharp/ql/src/semmle/code/csharp/Assignable.qll

@@ -76,6 +76,11 @@ class AssignableRead extends AssignableAccess {
     not nameOfChild(_, this)
   }
 
+  pragma[noinline]
+  private ControlFlow::Node getAnAdjacentReadSameVar() {
+    Ssa::Internal::adjacentReadPairSameVar(this.getAControlFlowNode(), result)
+  }
+
   /**
    * Gets a next read of the same underlying assignable. That is, a read
    * that can be reached from this read without passing through any other reads,
@@ -102,7 +107,7 @@ class AssignableRead extends AssignableAccess {
    */
   AssignableRead getANextRead() {
     forex(ControlFlow::Node cfn | cfn = result.getAControlFlowNode() |
-      Ssa::Internal::adjacentReadPairSameVar(this.getAControlFlowNode(), cfn)
+      cfn = this.getAnAdjacentReadSameVar()
     )
   }
 

csharp/ql/src/semmle/code/csharp/dataflow/DataFlow.qll

@@ -704,6 +704,7 @@ module DataFlow {
       )
     }
 
+    pragma[nomagic]
     private ControlFlowElement getANonExactScopeChild(ControlFlowElement scope) {
       scope = getAScope(false) and
       result = scope