protected virtual MethodDesc ResolveVirtualMethod(MethodDesc declMethod, DefType implType, out CORINFO_DEVIRTUALIZATION_DETAIL devirtualizationDetail)
{
devirtualizationDetail = CORINFO_DEVIRTUALIZATION_DETAIL.CORINFO_DEVIRTUALIZATION_UNKNOWN;
MethodDesc impl;
if (declMethod.OwningType.IsInterface)
{
if (declMethod.OwningType.IsCanonicalSubtype(CanonicalFormKind.Any) || implType.IsCanonicalSubtype(CanonicalFormKind.Any))
{
DefType[] implTypeRuntimeInterfaces = implType.RuntimeInterfaces;
int canonicallyMatchingInterfacesFound = 0;
DefType canonicalInterfaceType = (DefType)declMethod.OwningType.ConvertToCanonForm(CanonicalFormKind.Specific);
for (int i = 0; i < implTypeRuntimeInterfaces.Length; i++)
{
DefType runtimeInterface = implTypeRuntimeInterfaces[i];
if (canonicalInterfaceType.HasSameTypeDefinition(runtimeInterface) &&
runtimeInterface.ConvertToCanonForm(CanonicalFormKind.Specific) == canonicalInterfaceType)
{
canonicallyMatchingInterfacesFound++;
if (canonicallyMatchingInterfacesFound > 1)
{
// We cannot resolve the interface as we don't know with exact enough detail which interface
// of multiple possible interfaces is being called.
devirtualizationDetail = CORINFO_DEVIRTUALIZATION_DETAIL.CORINFO_DEVIRTUALIZATION_MULTIPLE_IMPL;
return(null);
}
}
}
}
if (!implType.CanCastTo(declMethod.OwningType))
{
devirtualizationDetail = CORINFO_DEVIRTUALIZATION_DETAIL.CORINFO_DEVIRTUALIZATION_FAILED_CAST;
return(null);
}
impl = implType.ResolveInterfaceMethodTargetWithVariance(declMethod);
if (impl != null)
{
impl = implType.FindVirtualFunctionTargetMethodOnObjectType(impl);
}
else
{
MethodDesc dimMethod = null;
// This isn't the correct lookup algorithm for variant default interface methods
// but as we will drop any results we find in any case, it doesn't matter much.
// Non-variant dispatch can simply use ResolveInterfaceMethodToDefaultImplementationOnType
// but that implementation currently cannot handle variance.
MethodDesc defaultInterfaceDispatchDeclMethod = null;
foreach (TypeDesc iface in implType.RuntimeInterfaces)
{
if (iface == declMethod.OwningType)
{
defaultInterfaceDispatchDeclMethod = declMethod;
break;
}
if (iface.HasSameTypeDefinition(declMethod.OwningType) && iface.CanCastTo(declMethod.OwningType))
{
defaultInterfaceDispatchDeclMethod = iface.FindMethodOnTypeWithMatchingTypicalMethod(declMethod);
// Prefer to find the exact match, so don't break immediately
}
}
if (defaultInterfaceDispatchDeclMethod != null)
{
switch (implType.ResolveInterfaceMethodToDefaultImplementationOnType(defaultInterfaceDispatchDeclMethod, out dimMethod))
{
case DefaultInterfaceMethodResolution.Diamond:
case DefaultInterfaceMethodResolution.Reabstraction:
devirtualizationDetail = CORINFO_DEVIRTUALIZATION_DETAIL.CORINFO_DEVIRTUALIZATION_FAILED_DIM;
return(null);
case DefaultInterfaceMethodResolution.DefaultImplementation:
if (dimMethod.OwningType.HasInstantiation || (declMethod != defaultInterfaceDispatchDeclMethod))
{
// If we devirtualized into a default interface method on a generic type, we should actually return an
// instantiating stub but this is not happening.
// Making this work is tracked by https://github.com/dotnet/runtime/issues/9588
// In addition, we fail here for variant default interface dispatch
devirtualizationDetail = CORINFO_DEVIRTUALIZATION_DETAIL.CORINFO_DEVIRTUALIZATION_FAILED_DIM;
return(null);
}
else
{
impl = dimMethod;
}
break;
}
}
}
}
else
{
// The derived class should be a subclass of the base class.
// this check is perfomed via typedef checking instead of casting, as we accept canon methods calling exact types
TypeDesc checkType;
for (checkType = implType; checkType != null && !checkType.HasSameTypeDefinition(declMethod.OwningType); checkType = checkType.BaseType)
{
}
if ((checkType == null) || (checkType.ConvertToCanonForm(CanonicalFormKind.Specific) != declMethod.OwningType.ConvertToCanonForm(CanonicalFormKind.Specific)))
{
// The derived class should be a subclass of the base class.
devirtualizationDetail = CORINFO_DEVIRTUALIZATION_DETAIL.CORINFO_DEVIRTUALIZATION_FAILED_SUBCLASS;
return(null);
}
else
{
// At this point, the decl method may be only canonically compatible, but not an exact match to a method in the type hierarchy
// Convert it to an exact match. (Or if it is an exact match, the FindMethodOnTypeWithMatchingTypicalMethod will be a no-op)
declMethod = checkType.FindMethodOnTypeWithMatchingTypicalMethod(declMethod);
}
impl = implType.FindVirtualFunctionTargetMethodOnObjectType(declMethod);
if (impl != null && (impl != declMethod))
{
MethodDesc slotDefiningMethodImpl = MetadataVirtualMethodAlgorithm.FindSlotDefiningMethodForVirtualMethod(impl);
MethodDesc slotDefiningMethodDecl = MetadataVirtualMethodAlgorithm.FindSlotDefiningMethodForVirtualMethod(declMethod);
if (slotDefiningMethodImpl != slotDefiningMethodDecl)
{
// If the derived method's slot does not match the vtable slot,
// bail on devirtualization, as the method was installed into
// the vtable slot via an explicit override and even if the
// method is final, the slot may not be.
//
// Note the jit could still safely devirtualize if it had an exact
// class, but such cases are likely rare.
devirtualizationDetail = CORINFO_DEVIRTUALIZATION_DETAIL.CORINFO_DEVIRTUALIZATION_FAILED_SLOT;
impl = null;
}
}
}
return(impl);
}