Let's list camera compatibility successes and failures for the 80D, as some lenses are limited in support. First, there are 8 different levels of focus ability depending on the lens, from Canon's manual:
Group "A" uses all 45 focus points, and the center point is a double cross type.
Group "B" is the same as A, sans the double cross point
Group "C" has 45 points, but the outer 10 points are not cross type, if I interpret their terms correctly
Group "D" has 45 points, but the outer 30 are not cross type, e.g. only the center section points are cross-type
Group "E" has 35 points by losing the outer 10 points entirely
Group "F" has 35 points available, fewer cross type
Group "G" has 27 points Group "H" has one point only.
Here's a partial list of lenses and their group (please double-check the manual before purchase):
Group A: EF-S 17-55mm; primes 2.8 or faster; EF24-70mm (both types)
Group B: EF24-105 f/4; EF70-300
Group C: EF75-300, 100-300
Group D: 24-85, 55-200
Group E: 35-70; 28-70
Group F: 22-55
Group G: 100-400 w/ 1.4x; 200-400 w 1.4x and 2x
Group H: Long zoom lenses with teleconverters
The trick is to determine 3rd party lens compatibility. I'll start aspect of the discussion with this link to Tamron's site, where they acknowledge incompatibilities between certain Tamron lenses and the 80D's live view:
OK, so now for my experience.
Canon EF 24-105mm f/4 L: Excellent autofocusing in all aspects.
Tamron 70-200mm f/2.8 VC SP: Excellent autofocusing in viewfinder use, but locks the camera in live view so hard a battery removal is called for.
Tokina 11-16mm f/2.8: Excellent autofocusing in all aspects.
I don't know where my Tamron and Tokina fall within the group designations. If the focus point illumination is any indication, I'm guessing A, B, C, or D as I have all 45 points available.
I'll also hypothesize that the lens group designation is not an artificial designation as much as it is the ability of the camera to make use of the image coming through the lens, e.g. a factor of the lens quality and the focusing situation (f/8 at 500mm, etc.)