My mention of overhead was just how complicated it would be to
implement. The general algorithm is (for each become keyword):
* determine max stack size (consider all branches in all
recursive
contexts)
* allocate stack size for top-level function
* do normal TCE stuff (use existing stack for new call)
What's wrong with just allocating a new stack _in-place_ of
the old?
In other words make 'become' synonym for 'reuse the current
stack frame'.
Effectively you still stay in constant space that is maximum of
all functions being called.
That would work too. If scope() is disallowed, it doesn't matter
where the stack comes from. It's only slightly cheaper to reuse
the current stack (CPU), but making a new one would be lighter on
memory.
I see nice staff. My use case is optimizing virtual machine,
the one inside std.regex primarily.
Yeah, that is a great example! I've read some bug reports about
std.regex using a ton of memory, especially with CTFE. Since
regex is by definition a state machine, this would be a
particularly elegant fit (granted, backreferences et al break
that model, but it's still a nice metaphor).
The main problem I see is working with other compilers like
GCC/LLVM. If this can be done on those compilers, I don't see any
major hurdle to getting this implemented.
