It needs to match with the (large loadable) lowered closure type in the rest of
the program: Large types in the signature need to be passed indirectly.
rdar://127367321
An unchecked_trivial_bit_cast can go from a bigger type to a smaller
type. Therefore we must allocate stack storage for the operand type
rather than the result type. Otherwise, we can end up storing bigger
values into smaller storage -- not good.
rdar://128086028
Functions with c convention can have large direct arguments that are not
re-written by the LoadableByAddress pass before they get to reg2Mem
optimization.
https://github.com/apple/swift/issues/71757
