The layout changes to become relative-address based. For this to be
truly immutable (at least on Darwin), things like the RO data patterns
must be moved out of the pattern header. Additionally, compress the
pattern header so that we do not include metadata about patterns that
are not needed for the type.
Value metadata patterns just include the metadata kind and VWT.
The design here is meant to accomodate non-default instantiation
patterns should that become an interesting thing to support in the
future, e.g. for v-table specialization.
Change the "metadata base offset" variable into a "class metadata bounds"
variable that contains the base offset and the +/- bounds on the class.
Link this variable from the class descriptor when the class has a resilient
superclass; otherwise, store the +/- bounds there. Use this variable to
compute the immediate-members offset for various runtime queries. Teach the
runtime to fill it in lazily and remove the code to compute it from the
generated code for instantiation. Identify generic arguments with the start
of the immediate class metadata members / end of the {struct,enum} metadata
header and remove the generic-arguments offset from generic type descriptors.
Right now, field offsets come before generic arguments in instances
of a struct's metadata. It would be more resilient to put the generic
arguments first, since they're always used by compiler-generated code,
and cannot change resiliently, unlike fields.
Resolves: rdar://problem/36560486
We no longer need this for anything, so remove it from metadata
altogether. This simplifies logic for emitting type metadata and
makes type metadata smaller.
We still pass the parent metadata pointer to type constructors;
removing that is a separate change.
John McCall
Pavel Yaskevich
Slava Pestov