swift234

SIL: Add instructions to implement address-only unions.

Because union layout may interleave tag bits with payload data, we need to be able to efficiently inject and remove tag bits from an address-only union in-place. To do this, we'll model address-only union initialization by projecting out the data address (union_data_addr) and storing to it, then overlaying the tag bits (inject_union_addr). To dispatch and project out the data, we'll use a destructive_switch_union_addr instruction that clears any tag bits in-place necessary to give a valid data address.

Swift SVN r7589