This does add a little computational complexity because now every
freemem operation has to be tested for every allocation. This could be
improved with some more memoisation but I think it is easier to read
this way. Let me know if you would prefer me to change this to
pre-compute the normalised addresses each freemem operation is using.
Weirdly, this change resulted in a verifier failure for the fir.declare
in the previous test case. Maybe it was previously removed as dead code
and now it isn't. Anyway I fixed that too.
303249c449