The front derailleur cable felt a little slack. I thought maybe the cable had simply gone out of adjustment and the bike's fall had been a coincidence. Snugging the cable did not fix the shifting, but it did change the problem enough for me to notice that the front derailleur was not swinging in a smooth arc.
Shown at the center of this shot, the pivot rivet. Derailleur is Shimano 105.
Some older front derailleurs were held together with bolts that can loosen. Check your derailleur and snug these bolts every so often. The term Marvin bolts comes from the particular repair on which I failed to remember them soon enough.