[gsg]

push $1/pop %eax (6a 01 58) is shorter, but perhaps not the best idea.

[nayuki]

Actually, there is no 32-bit pop instruction in x86-64 mode. Your code won't work.

[gsg]

You're right: it should be pushq $1/pop %rax (which is also three bytes, although there will be a prefix byte for registers r8 through r15).