limit check insertion

[Stephen Weeks]

> > I would still like to hear opinions on the short term fix of
> > restricting limit check coalescing to basic blocks.
> 
> Meaning, let alloc(l) = sum of allocations in the block and setting
> limitCheck(l) = alloc(l)?

Yes, modulo threads and variable size allocations.

> Sounds cheap and quick (to write); I guess we need to see how it plays out
> in practice to determine how quickly we need to move to something else.
> I've got no objections to it.

I'll start on it tomorrow then.