/// <summary>
/// Attempts to resolve constrained call to <paramref name="interfaceMethod"/> into a concrete non-unboxing
/// method on <paramref name="constrainedType"/>.
/// The ability to resolve constraint methods is affected by the degree of code sharing we are performing
/// for generic code.
/// </summary>
/// <returns>The resolved method or null if the constraint couldn't be resolved.</returns>
public static MethodDesc TryResolveConstraintMethodApprox(this TypeDesc constrainedType, TypeDesc interfaceType, MethodDesc interfaceMethod, out bool forceRuntimeLookup)
{
forceRuntimeLookup = false;
// We can't resolve constraint calls effectively for reference types, and there's
// not a lot of perf. benefit in doing it anyway.
if (!constrainedType.IsValueType)
{
return(null);
}
// Non-virtual methods called through constraints simply resolve to the specified method without constraint resolution.
if (!interfaceMethod.IsVirtual)
{
return(null);
}
MethodDesc method;
MethodDesc genInterfaceMethod = interfaceMethod.GetMethodDefinition();
if (genInterfaceMethod.OwningType.IsInterface)
{
// Sometimes (when compiling shared generic code)
// we don't have enough exact type information at JIT time
// even to decide whether we will be able to resolve to an unboxed entry point...
// To cope with this case we always go via the helper function if there's any
// chance of this happening by checking for all interfaces which might possibly
// be compatible with the call (verification will have ensured that
// at least one of them will be)
// Enumerate all potential interface instantiations
// TODO: this code assumes no shared generics
Debug.Assert(interfaceType == interfaceMethod.OwningType);
method = constrainedType.ResolveInterfaceMethodToVirtualMethodOnType(genInterfaceMethod);
}
else if (genInterfaceMethod.IsVirtual)
{
method = constrainedType.FindVirtualFunctionTargetMethodOnObjectType(genInterfaceMethod);
}
else
{
// The method will be null if calling a non-virtual instance
// methods on System.Object, i.e. when these are used as a constraint.
method = null;
}
if (method == null)
{
// Fall back to VSD
return(null);
}
//#TryResolveConstraintMethodApprox_DoNotReturnParentMethod
// Only return a method if the value type itself declares the method,
// otherwise we might get a method from Object or System.ValueType
if (!method.OwningType.IsValueType)
{
// Fall back to VSD
return(null);
}
// We've resolved the method, ignoring its generic method arguments
// If the method is a generic method then go and get the instantiated descriptor
if (interfaceMethod.HasInstantiation)
{
method = method.MakeInstantiatedMethod(interfaceMethod.Instantiation);
}
Debug.Assert(method != null);
//assert(!pMD->IsUnboxingStub());
return(method);
}
private bool CanCompareValueTypeBits(MetadataType type)
{
Debug.Assert(type.IsValueType);
if (type.ContainsGCPointers)
{
return(false);
}
if (type.IsGenericDefinition)
{
return(false);
}
OverlappingFieldTracker overlappingFieldTracker = new OverlappingFieldTracker(type);
bool result = true;
foreach (var field in type.GetFields())
{
if (field.IsStatic)
{
continue;
}
if (!overlappingFieldTracker.TrackField(field))
{
// This field overlaps with another field - can't compare memory
result = false;
break;
}
TypeDesc fieldType = field.FieldType;
if (fieldType.IsPrimitive || fieldType.IsEnum || fieldType.IsPointer || fieldType.IsFunctionPointer)
{
TypeFlags category = fieldType.UnderlyingType.Category;
if (category == TypeFlags.Single || category == TypeFlags.Double)
{
// Double/Single have weird behaviors around negative/positive zero
result = false;
break;
}
}
else
{
// Would be a suprise if this wasn't a valuetype. We checked ContainsGCPointers above.
Debug.Assert(fieldType.IsValueType);
// If the field overrides Equals, we can't use the fast helper because we need to call the method.
if (fieldType.FindVirtualFunctionTargetMethodOnObjectType(_objectEqualsMethod).OwningType == type)
{
result = false;
break;
}
if (!CanCompareValueTypeBits((MetadataType)fieldType))
{
result = false;
break;
}
}
}
// If there are gaps, we can't memcompare
if (result && overlappingFieldTracker.HasGaps)
{
result = false;
}
return(result);
}