What is the TRCLK pin Trace Clock pin?

I'm working on my documentation for a TM4C1294XL project and I see 5 pins/functions associated with Trace.  TRCLK, TRD0, TRD1, TRD2, TRD4.

What module uses these?  I couldn't find them defined in any of the documentation except for the GPIOPCTL PMCx Bit Field Encoding. 

Thanks!