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, und H. Mössenböck. Proceedings of the 2019 27th ACM Joint Meeting on European Software Engineering Conference and Symposium on the Foundations of Software Engineering, ACM, (August 2019)
T. Zhou, M. Jantz, P. Kulkarni, K. Doshi, und V. Sarkar. Proceedings of the 28th International Conference on Compiler Construction, Seite 147--158. New York, NY, USA, ACM, (2019)