Start outline storage support: Add swift_allocBox/deallocBox

Code using the outline heap storage path will crash and burn because
support is incomplete. But at least inline storage existential
inhabitants should compile and run.

stdlib/public/SwiftShims/swift/shims/EmbeddedShims.h

@@ -83,6 +83,51 @@ static inline void _swift_embedded_set_heap_object_metadata_pointer(void *object
   ((EmbeddedHeapObject *)object)->metadata = metadata;
 }
 
+typedef struct {
+  void  *initializeBufferWithCopyOfBufferFn;
+#if __has_feature(ptrauth_calls)
+  void  (* __ptrauth(0, 1, 0x04f8)  destroyFn)(void *, void*);
+#else
+  void  (*destroyFn)(void *, void*);
+#endif
+#if __has_feature(ptrauth_calls)
+  void* (* __ptrauth(0, 1, 0xe3ba) initializeWithCopyFn)(void*, void*, void*);
+#else
+  void* (*initializeWithCopyFn)(void*, void*, void*);
+#endif
+  void  *assignWithCopyFn;
+  void  *initializeWithTakeFn;
+  void  *assignWithTakeFn;
+  void  *getEnumTagSinglePayloadFn;
+  void  *storeEnumTagSinglePayload;
+  __swift_size_t size;
+  __swift_size_t stride;
+  unsigned flags;
+} EmbeddedValueWitnessTable;
+
+typedef struct {
+#if __has_feature(ptrauth_calls)
+  EmbeddedValueWitnessTable * __ptrauth(2, 1, 0x2e3f) vwt;
+#else
+  EmbeddedValueWitnessTable *vwt;
+#endif
+} EmbeddedMetaDataPrefix;
+
+static inline __swift_size_t _swift_embedded_metadata_get_size(void *metadata) {
+  EmbeddedMetaDataPrefix *fullmeta = (EmbeddedMetaDataPrefix*)&((void **)metadata)[-1];
+  return fullmeta->vwt->size;
+}
+
+static inline __swift_size_t _swift_embedded_metadata_get_align_mask(void *metadata) {
+  EmbeddedMetaDataPrefix *fullmeta = (EmbeddedMetaDataPrefix*)&((void **)metadata)[-1];
+
+  unsigned flags =  fullmeta->vwt->flags;
+  unsigned embeddedValueWitnessTableFlagsMask = 0xFF;
+
+  return flags & embeddedValueWitnessTableFlagsMask;
+}
+
+
 #ifdef __cplusplus
 } // extern "C"
 #endif

stdlib/public/core/EmbeddedRuntime.swift

@@ -262,6 +262,34 @@ public func swift_allocEmptyBox() -> Builtin.RawPointer {
 }
 
 
+@_silgen_name("swift_allocBox")
+public func swift_allocBox(metadata: Builtin.RawPointer) -> (Builtin.RawPointer, Builtin.RawPointer) {
+  let alignMask = Int(unsafe _swift_embedded_metadata_get_align_mask(UnsafeMutableRawPointer(metadata)))
+  let size = Int(unsafe _swift_embedded_metadata_get_size(UnsafeMutableRawPointer(metadata)))
+  let headerSize = unsafe MemoryLayout<Int>.size + MemoryLayout<UnsafeRawPointer>.size
+  let headerAlignMask = unsafe MemoryLayout<UnsafeRawPointer>.alignment - 1
+  let startOfBoxedValue = ((headerSize + alignMask) & ~alignMask)
+  let requiredSize: Int = startOfBoxedValue + size
+  let requiredAlignmentMask: Int = alignMask | headerAlignMask
+
+  let p = unsafe swift_slowAlloc(requiredSize, requiredAlignmentMask)!
+  let object = unsafe p.assumingMemoryBound(to: HeapObject.self)
+
+  unsafe _swift_embedded_set_heap_object_metadata_pointer(object, UnsafeMutableRawPointer(metadata))
+  unsafe object.pointee.refcount = 1
+
+  let boxedValueAddr = unsafe UnsafeMutableRawPointer(p).advanced(by: startOfBoxedValue)
+
+  return (object._rawValue, boxedValueAddr._rawValue)
+}
+
+@_cdecl("swift_deallocBox")
+public func swift_deallocBox(object: Builtin.RawPointer) {
+  unsafe free(UnsafeMutableRawPointer(object))
+}
+
+
+
 /// Refcounting
 
 func isValidPointerForNativeRetain(object: Builtin.RawPointer) -> Bool {

test/embedded/existential.swift

@@ -117,6 +117,33 @@ func test2(_ p: any Derived) {
   p.b()
 }
 
+
+protocol ValuePrinter {
+    func printValue()
+}
+protocol WithAssoc {
+    associatedtype Assoc : ValuePrinter
+    func a() -> Assoc
+}
+
+extension Int : ValuePrinter {
+    func printValue() {
+        print("my value: \(self)")
+    }
+}
+
+struct ConformWithAssoc : WithAssoc {
+  var x = 1
+  func a() -> Int {
+    return x
+  }
+}
+
+func test3(_ p: any WithAssoc) {
+  let x = p.a()
+  x.printValue()
+}
+
 @main
 struct Main {
   static func main() {
@@ -131,9 +158,11 @@ struct Main {
 // OUTPUT: a MyEnum
 // OUTPUT: 5
 // OUTPUT: b MyEnum
+// OUTPUT: my value: 1
     test2(Implementor())
     test2(5)
     test2(MyStruct())
     test2(MyEnum.b(5))
+    test3(ConformWithAssoc())
   }
 }