DMD Source Guidance: Unused Return Values of Strictly Pure Function Calls

["Nordlöw"]

Does anybody know where in the DMD source I can figure out if the 
return value of a function call is used or not?

I'm trying to figure out how to implement automatic detection of 
unused return values from calls to strictly pure functions.

The closest I have come is the function functionParameters() in 
expression.c

Ideas anyone?