Previously, AsyncFunctionPointer constants were signed as code. That
was incorrect considering that these constants are in fact data. Here,
that is fixed.
rdar://76118522
The backs out of some early decisions we made about actor layout
that we don't need. Custom actors will use a different approach.
This should suffice for the remainder of rdar://70146827.
Previously, when a FunctionPointer whose kind was AsyncFunctionPointer
was resigned, the underlying function pointer was loaded from the
AsyncFunctionPointer struct and that value was signed. That was
incorrect: a resigned pointer to an AsyncFunctionPointer struct should
again be a pointer to an AsyncFunctionPointer struct. Here that error
is corrected and the result of resigning is again a pointer to an
AsyncFunctionPointer struct.
An AsyncFunctionPointer, defined in Task.h, is a struct consisting of
two i32s: (1) the relative address of the async function and (2) the
size of the async context to be allocated when calling that function.
Here, such structs are emitted for every async SILFunction that is
emitted.
For actor class's implementations of `enqueue(partialTask:)`, use a
fixed ptrauth discriminator. Paired with the fixed vtable location,
this allows one to invoke this operation on any native actor instance
without knowing the specific type.
Two protocol conformance descriptors are passed to
swift_compareProtocolConformanceDecriptors from generic metadata
accessors when there is a canonical prespecialization and one of the
generic arguments has a protocol requirement.
Previously, the descriptors were incorrectly being passed without
ptrauth processing: one from the witness table in the arguments that are
passed in to the accessor and one known statically.
Here, the descriptor in the witness table is authed using the
ProtocolConformanceDescriptor schema. Then, both descriptors are signed
using the ProtocolConformanceDescriptorsAsArguments schema. Finally, in
the runtime function, the descriptors are authed.
This became necessary after recent function type changes that keep
substituted generic function types abstract even after substitution to
correctly handle automatic opaque result type substitution.
Instead of performing the opaque result type substitution as part of
substituting the generic args the underlying type will now be reified as
part of looking at the parameter/return types which happens as part of
the function convention apis.
rdar://62560867
MSVC does not realize that the switch is exhaustive and requires that
the path is explicitly marked as unreachable. This silences the C4715
warning ("not all control paths return a value").
