C#: Speedup DispatchMethodOrAccessorCall::getAViableOverrider()

In addition to improved performance, the analysis no longer applies a closed-world
assumption to type parameters. That is, if the type of a receiver is a type parameter,
then the call may target any method of a compatible receiver type, not just the
types that actually instantiate the type parameter.

Author: hvitved

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

@@ -233,71 +233,61 @@ private module Internal {
   }
 
   pragma[noinline]
-  private predicate hasOverrider(OverridableCallable oc, ValueOrRefType t) {
-    exists(oc.getAnOverrider(t))
+  private predicate hasOverrider(OverridableCallable oc, Gvn::GvnType t) {
+    exists(oc.getAnOverrider(any(ValueOrRefType t0 | Gvn::getGlobalValueNumber(t0) = t)))
   }
 
   pragma[noinline]
-  private predicate hasCallable(OverridableCallable source, ValueOrRefType t, OverridableCallable c) {
+  private predicate hasCallable(OverridableCallable source, Gvn::GvnType t, OverridableCallable c) {
     c.getUnboundDeclaration() = source and
-    t.hasCallable(c) and
+    any(ValueOrRefType t0 | Gvn::getGlobalValueNumber(t0) = t).hasCallable(c) and
     hasOverrider(c, t) and
-    hasQualifierTypeOverridden0(t, _) and
-    hasQualifierTypeOverridden1(source, _)
+    source = any(DispatchMethodOrAccessorCall call).getAStaticTargetExt()
   }
 
-  pragma[noinline]
-  private Unification::ConstrainedTypeParameter getAConstrainedTypeParameterQualifierType(
-    DispatchMethodOrAccessorCall call
-  ) {
-    result = getAPossibleType(call.getQualifier(), false)
-  }
+  abstract private class DispatchMethodOrAccessorCall extends DispatchCallImpl {
+    pragma[noinline]
+    OverridableCallable getAStaticTargetExt() {
+      exists(OverridableCallable target | this.getAStaticTarget() = target |
+        result = target.getUnboundDeclaration()
+        or
+        result = target.getAnUltimateImplementor().getUnboundDeclaration()
+      )
+    }
 
-  pragma[noinline]
-  private predicate constrainedTypeParameterQualifierTypeSubsumes(
-    ValueOrRefType t, Unification::ConstrainedTypeParameter tp
-  ) {
-    tp = getAConstrainedTypeParameterQualifierType(_) and
-    tp.subsumes(t)
-  }
+    pragma[nomagic]
+    predicate hasQualifierTypeInherited(Type t) { t = getAPossibleType(this.getQualifier(), _) }
 
-  pragma[noinline]
-  private predicate hasQualifierTypeOverridden0(ValueOrRefType t, DispatchMethodOrAccessorCall call) {
-    hasOverrider(_, t) and
-    (
-      exists(Type t0, Type t1 |
-        t0 = getAPossibleType(call.getQualifier(), false) and
-        t1 = [t0, t0.(Unification::UnconstrainedTypeParameter).getAnUltimatelySuppliedType()]
+    pragma[noinline]
+    private predicate hasSubsumedQualifierType(Gvn::GvnType t) {
+      hasOverrider(_, t) and
+      exists(Type t0 |
+        t0 = getAPossibleType(this.getQualifier(), false) and
+        not t0 instanceof TypeParameter
       |
-        t = t1
+        t = Gvn::getGlobalValueNumber(t0)
         or
-        Unification::subsumes(t1, t)
+        Gvn::subsumes(Gvn::getGlobalValueNumber(t0), t)
       )
-      or
-      constrainedTypeParameterQualifierTypeSubsumes(t,
-        getAConstrainedTypeParameterQualifierType(call))
-    )
-  }
+    }
 
-  pragma[noinline]
-  private predicate hasQualifierTypeOverridden1(
-    OverridableCallable c, DispatchMethodOrAccessorCall call
-  ) {
-    exists(OverridableCallable target | call.getAStaticTarget() = target |
-      c = target.getUnboundDeclaration()
-      or
-      c = target.getAnUltimateImplementor().getUnboundDeclaration()
-    )
-  }
+    pragma[noinline]
+    private predicate hasConstrainedTypeParameterQualifierType(
+      Unification::ConstrainedTypeParameter tp
+    ) {
+      tp = getAPossibleType(this.getQualifier(), false)
+    }
 
-  abstract private class DispatchMethodOrAccessorCall extends DispatchCallImpl {
-    pragma[nomagic]
-    predicate hasQualifierTypeInherited(Type t) { t = getAPossibleType(this.getQualifier(), _) }
+    pragma[noinline]
+    private predicate hasUnconstrainedTypeParameterQualifierType() {
+      getAPossibleType(this.getQualifier(), false) instanceof
+        Unification::UnconstrainedTypeParameter
+    }
 
     pragma[nomagic]
-    predicate hasQualifierTypeOverridden(ValueOrRefType t, OverridableCallable c) {
-      hasQualifierTypeOverridden0(t, this) and
-      hasCallable(any(OverridableCallable oc | hasQualifierTypeOverridden1(oc, this)), t, c)
+    predicate hasSubsumedQualifierTypeOverridden(Gvn::GvnType t, OverridableCallable c) {
+      this.hasSubsumedQualifierType(t) and
+      hasCallable(any(OverridableCallable oc | oc = this.getAStaticTargetExt()), t, c)
     }
 
     /**
@@ -357,12 +347,33 @@ private module Internal {
     }
 
     pragma[nomagic]
-    private Callable getASubsumedStaticTarget0(Type t) {
+    private predicate contextArgHasConstrainedTypeParameterType(
+      DispatchCall ctx, Unification::ConstrainedTypeParameter tp
+    ) {
+      this.contextArgHasType(ctx, tp, false)
+    }
+
+    pragma[nomagic]
+    private predicate contextArgHasUnconstrainedTypeParameterType(DispatchCall ctx) {
+      this.contextArgHasType(ctx, any(Unification::UnconstrainedTypeParameter t), false)
+    }
+
+    pragma[nomagic]
+    private predicate contextArgHasNonTypeParameterType(DispatchCall ctx, Gvn::GvnType t) {
+      exists(Type t0 |
+        this.contextArgHasType(ctx, t0, false) and
+        not t0 instanceof TypeParameter and
+        t = Gvn::getGlobalValueNumber(t0)
+      )
+    }
+
+    pragma[nomagic]
+    private Callable getASubsumedStaticTarget0(Gvn::GvnType t) {
       exists(Callable staticTarget, Type declType |
         staticTarget = this.getAStaticTarget() and
         declType = staticTarget.getDeclaringType() and
         result = staticTarget.getUnboundDeclaration() and
-        Unification::subsumes(declType, t)
+        Gvn::subsumes(Gvn::getGlobalValueNumber(declType), t)
       )
     }
 
@@ -375,7 +386,8 @@ private module Internal {
     private Callable getASubsumedStaticTarget() {
       result = this.getAStaticTarget()
       or
-      result.getUnboundDeclaration() = this.getASubsumedStaticTarget0(result.getDeclaringType())
+      result.getUnboundDeclaration() =
+        this.getASubsumedStaticTarget0(Gvn::getGlobalValueNumber(result.getDeclaringType()))
     }
 
     /**
@@ -426,6 +438,12 @@ private module Internal {
       )
     }
 
+    pragma[noinline]
+    NonConstructedOverridableCallable getAViableOverrider0() {
+      getAPossibleType(this.getQualifier(), false) instanceof TypeParameter and
+      result.getAConstructingCallableOrSelf() = this.getAStaticTargetExt()
+    }
+
     /**
      * Gets a callable that is defined in a subtype of the qualifier type of this
      * call, and which overrides a static target of this call.
@@ -468,9 +486,22 @@ private module Internal {
      */
     private RuntimeCallable getAViableOverrider() {
       exists(ValueOrRefType t, NonConstructedOverridableCallable c |
-        this.hasQualifierTypeOverridden(t, c.getAConstructingCallableOrSelf()) and
+        this.hasSubsumedQualifierTypeOverridden(Gvn::getGlobalValueNumber(t),
+          c.getAConstructingCallableOrSelf()) and
         result = c.getAnOverrider(t)
       )
+      or
+      exists(NonConstructedOverridableCallable c |
+        c = this.getAViableOverrider0() and
+        result = c.getAnOverrider(_)
+      |
+        this.hasUnconstrainedTypeParameterQualifierType()
+        or
+        exists(Unification::ConstrainedTypeParameter tp |
+          this.hasConstrainedTypeParameterQualifierType(tp) and
+          tp.subsumes(result.getDeclaringType())
+        )
+      )
     }
 
     override RuntimeCallable getADynamicTarget() {
@@ -510,36 +541,40 @@ private module Internal {
     }
 
     pragma[nomagic]
-    private RuntimeCallable getAViableOverriderInCallContext0(
-      NonConstructedOverridableCallable c, ValueOrRefType t
-    ) {
-      result = this.getAViableOverrider() and
-      this.contextArgHasType(_, _, false) and
-      result = c.getAnOverrider(t)
+    private RuntimeCallable getAViableOverriderInCallContext0(Gvn::GvnType t) {
+      exists(NonConstructedOverridableCallable c |
+        result = this.getAViableOverrider() and
+        this.contextArgHasType(_, _, false) and
+        result = c.getAnOverrider(any(Type t0 | t = Gvn::getGlobalValueNumber(t0))) and
+        this.getAStaticTarget() = c.getAConstructingCallableOrSelf()
+      )
     }
 
     pragma[nomagic]
-    private RuntimeCallable getAViableOverriderInCallContext1(
-      NonConstructedOverridableCallable c, DispatchCall ctx
-    ) {
-      exists(ValueOrRefType t |
-        result = this.getAViableOverriderInCallContext0(c, t) and
-        exists(Type t0, Type t1 |
-          this.contextArgHasType(ctx, t0, false) and
-          t1 = [t0, t0.(Unification::UnconstrainedTypeParameter).getAnUltimatelySuppliedType()]
-        |
-          t = t1
-          or
-          Unification::subsumes(t1, t)
-        )
+    private predicate contextArgHasSubsumedType(DispatchCall ctx, Gvn::GvnType t) {
+      hasOverrider(_, t) and
+      exists(Gvn::GvnType t0 | this.contextArgHasNonTypeParameterType(ctx, t0) |
+        t = t0
+        or
+        Gvn::subsumes(t0, t)
       )
     }
 
     pragma[nomagic]
     private RuntimeCallable getAViableOverriderInCallContext(DispatchCall ctx) {
-      exists(NonConstructedOverridableCallable c |
-        result = this.getAViableOverriderInCallContext1(c, ctx) and
-        this.getAStaticTarget() = c.getAConstructingCallableOrSelf()
+      exists(Gvn::GvnType t |
+        result = this.getAViableOverriderInCallContext0(t) and
+        this.contextArgHasSubsumedType(ctx, t)
+      )
+      or
+      result = this.getAViableOverrider() and
+      (
+        this.contextArgHasUnconstrainedTypeParameterType(ctx)
+        or
+        exists(Unification::ConstrainedTypeParameter tp |
+          this.contextArgHasConstrainedTypeParameterType(ctx, tp) and
+          tp.subsumes(result.getDeclaringType())
+        )
       )
     }