C#: Dispatch library performance tweaks

- Restrict `OverridableCallable::getAnOverrider(ValueOrRefType t)` to types `t`
  that are sub types of the callable's declaring type.
- Use explicit recursion in `OverridableCallable::getInherited()`.

csharp/ql/src/semmle/code/csharp/dispatch/Dispatch.qll

@@ -202,7 +202,7 @@ private module Internal {
      * Gets a non-exact (see `hasQualifierType()`) qualifier type of this call
      * that does not contain type parameters.
      */
-    TypeWithoutTypeParameters getANonExactQualifierTypeWithoutTypeParameters() {
+    private TypeWithoutTypeParameters getANonExactQualifierTypeWithoutTypeParameters() {
       exists(Type qualifierType | hasQualifierType(qualifierType, false) |
         // Qualifier type contains no type parameters: use it
         result = qualifierType
@@ -220,6 +220,20 @@ private module Internal {
         result = qualifierType.(QualifierTypeWithTypeParameters).getAPotentialInstance()
       )
     }
+
+    /**
+     * Gets a non-exact (see `hasQualifierType()`) qualifier type of this call.
+     */
+    ValueOrRefType getANonExactQualifierType() {
+      exists(TypeWithoutTypeParameters t |
+        t = this.getANonExactQualifierTypeWithoutTypeParameters()
+      |
+        result.(ConstructedType).getUnboundGeneric() = t
+        or
+        not t instanceof UnboundGenericType and
+        result = t
+      )
+    }
   }
 
   private class DynamicFieldOrProperty extends Assignable {
@@ -480,9 +494,9 @@ private module Internal {
      * qualifier types are `B.M` and `C.M`, `C.M`, and none, respectively.
      */
     private RuntimeInstanceMethod getAViableOverrider() {
-      exists(TypeWithoutTypeParameters t, NonConstructedOverridableMethod m |
-        t = getANonExactQualifierTypeWithoutTypeParameters() and
-        getAStaticTarget() = m.getAConstructingMethodOrSelf() and
+      exists(ValueOrRefType t, NonConstructedOverridableMethod m |
+        t = this.getANonExactQualifierType() and
+        this.getAStaticTarget() = m.getAConstructingMethodOrSelf() and
         result = m.getAnOverrider(t)
       )
     }
@@ -620,9 +634,9 @@ private module Internal {
      * respectively.
      */
     private RuntimeAccessor getAViableOverrider() {
-      exists(TypeWithoutTypeParameters t |
-        t = getANonExactQualifierTypeWithoutTypeParameters() and
-        result = getAStaticTarget().(OverridableAccessor).getAnOverrider(t)
+      exists(ValueOrRefType t |
+        t = this.getANonExactQualifierType() |
+        result = this.getAStaticTarget().(OverridableAccessor).getAnOverrider(t)
       )
     }
   }

csharp/ql/src/semmle/code/csharp/dispatch/OverridableCallable.qll

@@ -135,27 +135,33 @@ class OverridableCallable extends Callable {
    * - `C2.M = C2.M.getInherited(C3)`.
    */
   Callable getInherited(SourceDeclarationType t) {
-    exists(Callable sourceDecl | result = getInherited1(t, sourceDecl) |
+    exists(Callable sourceDecl | result = this.getInherited2(t, sourceDecl) |
       hasSourceDeclarationCallable(t, sourceDecl)
     )
   }
 
-  private Callable getInherited0(SourceDeclarationType t) {
+  private Callable getInherited0(ValueOrRefType t) {
     // A (transitive, reflexive) overrider
-    t = this.hasOverrider(result).getASubType*().getSourceDeclaration()
+    t = this.hasOverrider(result)
+    or
+    // A (transitive) overrider of an interface implementation
+    t = this.hasOverridingImplementor(result)
+    or
+    exists(ValueOrRefType mid | result = this.getInherited0(mid) | t = mid.getASubType())
+  }
+
+  private Callable getInherited1(SourceDeclarationType t) {
+    exists(ValueOrRefType t0 | result = getInherited0(t0) | t = t0.getSourceDeclaration())
     or
     // An interface implementation
     exists(ValueOrRefType s |
       result = getAnImplementorSubType(s) and
       t = s.getSourceDeclaration()
     )
-    or
-    // A (transitive) overrider of an interface implementation
-    t = this.hasOverridingImplementor(result).getASubType*().getSourceDeclaration()
   }
 
-  private Callable getInherited1(SourceDeclarationType t, Callable sourceDecl) {
-    result = this.getInherited0(t) and
+  private Callable getInherited2(SourceDeclarationType t, Callable sourceDecl) {
+    result = this.getInherited1(t) and
     sourceDecl = result.getSourceDeclaration()
   }
 
@@ -171,9 +177,42 @@ class OverridableCallable extends Callable {
     result = c.getDeclaringType()
   }
 
+  private predicate isDeclaringSubType(ValueOrRefType t) {
+    t = this.getDeclaringType()
+    or
+    exists(ValueOrRefType mid | isDeclaringSubType(mid) | t = mid.getASubType())
+  }
+
+  pragma[noinline]
+  private Callable getAnOverrider0(ValueOrRefType t) {
+    not this.declaredInTypeWithTypeParameters() and
+    (
+      // A (transitive) overrider
+      result = this.getAnOverrider+() and
+      t = result.getDeclaringType()
+      or
+      // An interface implementation
+      result = this.getAnImplementorSubType(t)
+      or
+      // A (transitive) overrider of an interface implementation
+      result = this.getAnOverridingImplementor() and
+      t = result.getDeclaringType()
+    )
+  }
+
+  private Callable getAnOverrider1(ValueOrRefType t) {
+    result = this.getAnOverrider0(t)
+    or
+    exists(ValueOrRefType mid | result = this.getAnOverrider1(mid) |
+      t = mid.getABaseType() and
+      this.isDeclaringSubType(t)
+    )
+  }
+
   /**
-   * Gets a callable defined in a sub type of `t` that overrides/implements
-   * this callable, if any.
+   * Gets a callable defined in a sub type of `t` (which is itself a sub type
+   * of this callable's declaring type) that overrides/implements this callable,
+   * if any.
    *
    * The type `t` may be a constructed type: For example, if `t = C<int>`,
    * then only callables defined in sub types of `C<int>` (and e.g. not
@@ -181,39 +220,7 @@ class OverridableCallable extends Callable {
    * contains a callable that overrides this callable, then only if `C2<int>`
    * is ever constructed will the callable in `C2` be considered valid.
    */
-  Callable getAnOverrider(TypeWithoutTypeParameters t) {
-    exists(OverridableCallable oc, ValueOrRefType sub |
-      result = oc.getAnOverriderAux(sub) and
-      t = oc.getAnOverriderBaseType(sub) and
-      oc = getABoundInstance()
-    )
-  }
-
-  // predicate folding to get proper join order
-  private Callable getAnOverriderAux(ValueOrRefType t) {
-    not declaredInTypeWithTypeParameters() and
-    (
-      // A (transitive) overrider
-      result = getAnOverrider+() and
-      t = result.getDeclaringType()
-      or
-      // An interface implementation
-      result = getAnImplementorSubType(t)
-      or
-      // A (transitive) overrider of an interface implementation
-      result = getAnOverridingImplementor() and
-      t = result.getDeclaringType()
-    )
-  }
-
-  private TypeWithoutTypeParameters getAnOverriderBaseType(ValueOrRefType t) {
-    exists(getAnOverriderAux(t)) and
-    exists(Type t0 | t0 = t.getABaseType*() |
-      result = t0
-      or
-      result = t0.(ConstructedType).getUnboundGeneric()
-    )
-  }
+  Callable getAnOverrider(ValueOrRefType t) { result = this.getABoundInstance().getAnOverrider1(t) }
 
   /**
    * Gets a bound instance of this callable.
@@ -264,7 +271,7 @@ class OverridableMethod extends Method, OverridableCallable {
     result = OverridableCallable.super.getInherited(t)
   }
 
-  override Method getAnOverrider(TypeWithoutTypeParameters t) {
+  override Method getAnOverrider(ValueOrRefType t) {
     result = OverridableCallable.super.getAnOverrider(t)
   }
 }
@@ -311,7 +318,7 @@ class OverridableAccessor extends Accessor, OverridableCallable {
     result = OverridableCallable.super.getInherited(t)
   }
 
-  override Accessor getAnOverrider(TypeWithoutTypeParameters t) {
+  override Accessor getAnOverrider(ValueOrRefType t) {
     result = OverridableCallable.super.getAnOverrider(t)
   }
 }