Is Optimizer smart enough?

Hi,

Just for curiosity: suppose there is an excellent index frequently picked by
the optimizer. Suppose now that this index became extremelly fragmented with
thousands of updates. Without a REINDEX, will Optimizer still pick it? Or the
optimizer is smart enough to detect index fragmentation and discard it?

Is there something that I could do in btcostesimate function to detect
increasing index fragmentation?

best regards,

Eduardo Morelli