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:
T. Zhou, M. Jantz, P. Kulkarni, K. Doshi, and V. Sarkar. Proceedings of the 28th International Conference on Compiler Construction, page 147--158. New York, NY, USA, ACM, (2019)