[LLVMdev] Tagged (Disjoint) Unions

[Chris Lattner]

On Wed, 3 May 2006, Ben Chambers wrote:
> I realize I *COULD* do it as a pair of an integer tag and the data, or any of 
> the numerous ways that have been devised for representing such types in other 
> functional languages.

Yup, you should treat LLVM as a slightly-higher level machine language. 
As such, you should lower it into an explicit "union" (using pointer casts 
etc).

> The problem that I see is that any optimizations for 
> which LLVM needs types to perform would basically be prohibited this 
> technique.  So, I guess what I'm asking is, is there a way of representing 
> tagged union types in LLVM that doesn't prevent providing accurate type 
> information?

No, there isn't.

-Chris

-- 
http://nondot.org/sabre/
http://llvm.org/