Iirc x87 was even worse on some processors depending on the processor state, the processor could cache the CPU state on context switch and revert the x87 regist

Iirc x87 was even worse on some processors depending on the processor state, the processor could cache the CPU state on context switch and revert the x87 register to a f64, leading to irreproducibility at the runtime level (randomly fails if you get an unlucky thread thrash)