Provide new swift_{alloc,dealloc,project}Box2 entry points that allocate, project, and deallocate typed boxes using runtime-instantiated metadata. Give these a new metadata kind, so that external tools recognize the difference and can interpret the metadata appropriately.
Swift SVN r29714
We were missing -_tryRetain, -_isDeallocating, -allowsWeakReference and -retainWeakReference implementations on SwiftObject, so forming an ObjC weak reference to a pure Swift object always failed and produced a nil reference. Fixes rdar://problem/18637774.
This can be reapplied now that we properly call objc_destructInstance on deallocation.
Swift SVN r23070
We were missing -_tryRetain, -_isDeallocating, -allowsWeakReference and -retainWeakReference implementations on SwiftObject, so forming an ObjC weak reference to a pure Swift object always failed and produced a nil reference. Fixes rdar://problem/18637774.
Swift SVN r22710
The allocator's crimes include:
* It uses OS SPI that must not be used by non-OS apps.
* It does not play well with memory debugging tools like Instruments.
* It does not return memory to the OS in response to memory pressure.
* It is less tested than we would like because many configurations
inadvertently turn it off (such as running from Xcode).
* Its per-thread magazine implementation does not actually work.
* Its "try alloc" flag is incompletely implemented and never used.
* Its "zero fill" flag is unimplemented and inconsistently used.
Swift SVN r20757
Rather than go through reentrant and problematic contortions to make Swift
work with the existing Instruments hooks, they agreed to just patch some
globals that we provide to get their logic to be activated.
Swift SVN r17144
