cmov (i.e. conditional move) doesn't branch. By branch here, we mean "at point at which the successor program counter value might be one of two locations." It's true that this _does_ have security implications, however this is frequently used as a term of art by performance engineers (see https://www.youtube.com/watch?v=g-WPhYREFjk for example).
> And it doesn't really matter whether a branch can be well predicted.
A properly predicted branch can be _faster_ than a cmov instruction, however the important point is avoiding the branch mispredict. The fact that we're using cmov is beside the point. We could achieve a similar effect by performing a subtraction and doing bitwise arithmetic to extract the sign bit (which, in effect, performs a comparison).
> And it doesn't really matter whether a branch can be well predicted.
I'm not so sure this is true. See https://lemire.me/blog/2019/10/15/mispredicted-branches-can-... as an example.
A properly predicted branch can be _faster_ than a cmov instruction, however the important point is avoiding the branch mispredict. The fact that we're using cmov is beside the point. We could achieve a similar effect by performing a subtraction and doing bitwise arithmetic to extract the sign bit (which, in effect, performs a comparison).