🚀 go-pugleaf

Posted back in mid-1985:
> Description:
> 	The f77 VAX code generator creates illegal instructions ("cvtll")
> 	whenever the target of an 'assign' statement is an integer*2
> 	variable.
> 
> Repeat-by:
> 	Run the following program through the f77 compiler:
> 
> 	integer*2 i
> 	assign 10 to i
> 	goto i
> 10	continue
> 	end

I just got around to looking at this problem,
originally reported for VAX 4.2BSD f77, using
the VAX SVR2 f77.  It has a similar problem,
not in the code generator, but in the optimizer
(/lib/c2).  The optimizer removes the labeled
"ret" that is the target of the goto, because
it doesn't realize that the CVTLW (of the label
into a variable which is then indirectly jumped
through for the goto) is a label reference.
The CVTLL seems to be a Berkeley special..

ASSIGN moves a label, NOT an integer, into the
assign variable, which for that reason must
not be an INTEGER*2.  The compiler should,
however, have warned about this user error.