[LLVMdev] Newbie Question: not using local variables

[Brian Hurt]

I'm writing an ML-like language, and using LLVM as my target back end.  I 
have one question though, and thought I'd throw it out onto the list.  In 
my language, variables aren't mutable- once assigned, they can be 
shadowed, but not changed.  And shadowing of variables is handled by 
alpha-renaming.  What I mean by this that when I see:
 	let x = 3 in ...
the value of x can not be changed.  It can be shadowed, like:
 	let x = f () in
 	let x = x + 4 in
 	...
but one of the first things I do is rename all the variables so they're 
unique, so the above code might get changed into:
 	let x_5734 = f () in
 	let x_8643 = x_5734 + 4 in
 	...

Now, my question is this: is there any downside to not having any 
stack-based local variables at all- just put everything into registers and 
let the register allocation code decide what needs to get spilled onto the 
stack?  In other words, is there any problem with generating the following 
IR for the above code:
 	%r17 = call i64 @f(i64 0)
 	%r18 = add i64 %r17 4

The upside of doing this is simpler code generation, and hopefully more 
efficient code, as I am explicitly telling the optimizer I don't care 
where this variable lives.

But, I'm somewhat worried that by not having any local variables at all, 
this may put too much pressure on the register allocator (especially for 
large functions).  Also, how to attach debugging information to a register 
is something I need to figure out.

Thoughts?  Opinions?  Is this a good way to proceed, or a bad way?

Brian