When the SelfMetadata in a witness thunk is the tuple type (repeat each Self),
we can fulfill the pack shape and type metadata for Pack{repeat each Self}
from tuple metadata.
The length is trivially projected; the type metadata pack is slightly more
involved, because tuple metadata stores a list of element/offset pairs, so
we must stack allocate a pack and fill it in.
Deallocate dynamic allocas done for metadata/wtable packs. These
stackrestore calls are inserted on the dominance frontier and then stack
nesting is fixed up. That was achieved as follows:
Added a new IRGen pass PackMetadataMarkerInserter; it
- determines if there are any instructions which might allocate on-stack
pack metadata
- if there aren't, no changes are made
- if there are, alloc_pack_metadata just before instructions that could
allocate pack metadata on the stack and dealloc_pack_metadata on the
dominance frontier of those instructions
- fixup stack nesting
During IRGen, the allocations done for metadata/wtable packs are
recorded and IRGenSILFunction associates them with the instruction that
lowered. It must be the instruction after some alloc_pack_metadata
instruction. Then, when visiting the dealloc_pack_metadata instructions
corresponding to that alloc_pack_metadata, deallocate those packs.
When allocating, the shape is computed, and it (its constant value if
any) is needed when deallocating, so return the shape along with the
address. And when deallocating, accept the shape, which the client
received during allocation, rather than requiring that the caller
compute the fixed size.
When a metadata pack is heap allocated, the pointer's LSB is set.
But lldb is expecting a real pointer. So mask it off.
Companion PR has a test: https://github.com/apple/llvm-project/pull/6961
rdar://110195273
Previously, only the element archetypes that corresponded to the
relevant pack generic parameters were bound, and the wtables that were
bound for them were based on looking up what they conform to. Here, the
requirements of the generic signature are used to find which archetypes
must be bound to metadata and which conformances must be bound to
wtables.
Call out to the infrastructure for emitting witness table packs to emit
references to individual witness tables when binding opened archetypes
during open_pack_element.
