If I recall, we got the typesetter (troff) tape in between V6 and the later (I think we got PWB next then V7).    It had a compiler on it.    I presume that it was needed to compile troff, but most of us installed it as a more up to date C compiler.    If I recall properly (and boy my mind is hazy on this), is that it supported the “new” += syntax while warning that =+ was deprecated.  

At some point, the structure elements being made unique to the structure they were defined in, and the ability to assign/pass structures got supported, though I thought that was the compiler that came with V7.

I’m still annoyed they didn’t fix arrays when they fixed structs.