[Joe, Roman, sorry for resend, I got the e-mail group wrong]
In SuperMethodInst's verifier, we have:
require(CMI->getType() == TC.getConstantType(CMI->getMember()),
"result type of super_method must match type of method");
I think this assumption was valid when we only allowed super_method on foreign
classes, without needing to worry about reabstractions. Now that we're allowing
super_method with operands of native class type which can be generic, does this
check make sense anymore?
Consider the following:
class Parent<A> {
let x: A
required init(x: A) { self.x = x }
}
class Child : Parent<String> {
required init(x: String) {
super.init(x: x)
}
}
class Grandchild : Child {}
Here, the vtable thunks for their initializers have respective types:
$@convention(method) <T> (@in T, @owned Base<T>) -> @owned Base<T>
$@convention(method) (@in String, @owned Child) -> @owned Child
$@convention(method) (@in String, @owned Grandchild) -> @owned Grandchild
However, the real backing implementations have these respective types:
$@convention(method) <T> (@in T, @owned Base<T>) -> @owned Base<T>
$@convention(method) (@owned String, @owned Child) -> @owned Child
$@convention(method) (@owned String, @owned Grandchild) -> @owned Grandchild
So, Child and Grandchild have abstraction differences because their
initializers aren't generic. When I make a super_method instruction, the
constant appears to always point to the backing implementation, not the thunk,
so I needed to get the overridden vtable entry from the constant and I think
that's reasonable. That gives me:
super_method %10 : $Child, #Base.init!initializer.1 : <T> Base<T>.Type -> (x:
T) -> Base<T> , $@convention(method) <τ_0_0> (@in τ_0_0, @owned Base<τ_0_0>) ->
@owned Base<τ_0_0>
and
super_method %6 : $Grandchild, #Child.init!initializer.1 : Child.Type -> (x:
String) -> Child , $@convention(method) (@in String, @owned Child) -> @owned
Child
which look good to me.
With my changes today to fix generic substitutions of partial super methods and
getting the right type from the vtable, if I disable that verifier check,
devirtualization works correctly with super_method instructions.
Is this a problem with SILDeclRef or is this check simply no longer valid in
the verifier? If so, I wonder what the suitable replacement check should be.
Maybe something like:
if the constant is foreign:
do the original check
else:
require super_method's result type == vtable entry's function type (as opposed
to the backing implementation)
David_______________________________________________
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