This is not the first one. Skylake (and a few others) have a "well-known" false dependency bug in popcnt. It's listed in the skylake erratum as "POPCNT Instru

This is not the first one. Skylake (and a few others) have a "well-known" false dependency bug in popcnt. It's listed in the skylake erratum as "POPCNT Instruction May Take Longer to Execute than Expected".