> setcc actually does depend on the previous value of the register, because it only comes in the low-byte variants

You should be able to break the dependency and avoid the partial register stall by doing: movzx eax, ax

See: https://stackoverflow.com/questions/41573502/why-doesnt-gcc-... ; https://software.intel.com/en-us/forums/intel-isa-extensions... ; https://www.agner.org/optimize/microarchitecture.pdf (section 6.8)