As of this writing (but perhaps not for very much longer!) the four mainstream compilers on Godbolt Compiler Explorer give four different answers for this simple C++ program:
M. Rigger, S. Marr, B. Adams, и H. Mössenböck. Proceedings of the 2019 27th ACM Joint Meeting on European Software Engineering Conference and Symposium on the Foundations of Software Engineering, ACM, (августа 2019)
T. Zhou, M. Jantz, P. Kulkarni, K. Doshi, и V. Sarkar. Proceedings of the 28th International Conference on Compiler Construction, стр. 147--158. New York, NY, USA, ACM, (2019)
G. Chari, D. Garbervetsky, и S. Marr. Proceedings of the 11th Workshop on Implementation, Compilation, Optimization of Object-Oriented Languages, Programs and Systems, стр. 5. (19.06.2017)