I don't think that you can consider CPUs to be bug-free. Just to pick one, Intel got SYSRET wrong: https://blog.xenproject.org/2012/06/13/the-intel-sysret-priv...
https://en.wikipedia.org/wiki/Pentium_FDIV_bug
And who knows what happens or what bugs are fixed when intel/amd push new firmware to the chip.
https://en.wikipedia.org/wiki/Pentium_FDIV_bug