runtime: add runtime functions for stack promotion of buffers.

These functions are usually lowered away, but can remain if SIL optimizations run but not llvm optimizations.
This is only a workaround. I hope that I can remove the functions soon when we have a better support for buffers in SIL.

Author: eeckstein

stdlib/public/runtime/HeapObject.cpp

@@ -104,6 +104,25 @@ extern "C" HeapObject* swift_bufferAllocate(
   return swift::swift_allocObject(bufferType, size, alignMask);
 }
 
+/// \brief Another entrypoint for swift_bufferAllocate.
+/// It is generated by the compiler in some corner cases, e.g. if an serialized
+/// optimzed module is imported into a non-optimized main module.
+/// TODO: This is only a workaround. Remove this function as soon as we can
+/// get rid of the llvm SwiftStackPromotion pass.
+extern "C" HeapObject* swift_bufferAllocateOnStack(
+  HeapMetadata const* bufferType, size_t size, size_t alignMask) {
+  return swift::swift_allocObject(bufferType, size, alignMask);
+}
+
+/// \brief Called at the end of the lifetime of an object returned by
+/// swift_bufferAllocateOnStack.
+/// It is generated by the compiler in some corner cases, e.g. if an serialized
+/// optimzed module is imported into a non-optimized main module.
+/// TODO: This is only a workaround. Remove this function as soon as we can
+/// get rid of the llvm SwiftStackPromotion pass.
+extern "C" void swift_bufferDeallocateFromStack(HeapObject *) {
+}
+
 extern "C" intptr_t swift_bufferHeaderSize() { return sizeof(HeapObject); }
 
 /// A do-nothing destructor for POD metadata.