The only luxury sedans that GM makes are Buicks and Cadillacs and they aren't serious competitors in this segment.  The true premium marques are Mercedes, BMW and Audi and they each sell about 400,000 units of their C-Class, 3-series and A4 sedans, respectively.  Hopefully Telsa can ramp M3 production to those levels.  I've owned a BMW and the Model 3 will be a serious challenger.

Tesla Model S Crushes Large Luxury Car Competition (H1 2017 US Sales)
https://cleantechnica.com/2017/07/05/tesla-model-s-crushes-large-luxury-car-competition-h1-2017-us-sales/