[LLVMdev] Parametric polymorphism

[DeLesley Hutchins]

> I think many people were confused by this at first but an excellent counter
> example was provided in a previous thread: C99 ABIs can require that struct
> return values are returned via a pointer to a preallocated struct passed as
> an auxiliary argument *except* when you're talking about a C99 complex, in
> which case the return value is conveyed in a completely different way.

Thanks for the explanation.  That definitely does make type instantiation in
the IR a whole lot more annoying.

>> I don't expect magic.  If type specialization is implemented as an IR
>> pass, then why couldn't post-specialization IR optimizations be
>> performed?
>
> They could but my impression is that this will only ever be an academic
> exercise: I doubt LLVM's type system will ever be changed in such a
> fundamental way simply because the back-end is reaching maturity and that
> would destabilize a large part of the library but also because there is no
> clear advantage in doing that, not only for the majority of LLVM users but
> also in the context of its goals.

The majority of llvm users are using llvm to compile C, or things that are
similar to C.  People who want to compile something other than C (Haskell,
ML, OCaml, C#, etc.)  would benefit from from having type variables in the IR.

Focusing too much on one language leads to a limited VM.  Witness the
JVM (only supports Java), or MSIL (designed for C#, with other features
tacked on as an afterthought).

What you say about maturity and destabilization is probably true, but
that's more of a political problem or a manpower problem, not a technical
problem.

  -DeLesley