This thread [1] might give you some idea of the complexity involved in a similar issue. OTOH, if you see RAX being zeroed before using EAX, it is likely to be

This thread [1] might give you some idea of the complexity involved in a similar issue. OTOH, if you see RAX being zeroed before using EAX, it is likely to be about breaking false deps. 1: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86314 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86314