limit check insertion

[Henry Cejtin]

Sorry, I missed that the requirement was only that V(p, 0) was positive.

Isn't  hoisting  of limit checks into loops (which do allocation) required by
Stephen's set up?  If a loop does an allocation then the fact that there  are
an inifinite number of paths from the start which allocate any amount desired
in the loop will mean that without a limit check in the  loop  there  are  NO
correct annotations.

I  don't  think that any amount of moving limit checks can violate our notion
of safe-for-space.  The reason is that  it  only  costs  you  an  `arbitrary'
amount  for  non-tail  calls, and then you are still safe for space since you
can charge the fixed overhead to the non-tail call stack frame.

Don't get me wrong: we would be wasting space in the case  Matthew  mentions,
but  it  would  still be safe-for-space in our sense.  I.e., we already waste
that space in other ways (like by turning tail calls into non-tail calls).

As to the final paragraph in Matthew's note, I think that if you don't handle
that case you will do extra limit checks.  Not a failure, but not optimal.