[compiler-hacking] @inline attribute?

[Anil Madhavapeddy]

On 30 Oct 2014, at 16:22, Pierre Chambart <pierre.chambart at ocamlpro.com> wrote:
> 
> On 30/10/2014 17:01, Anil Madhavapeddy wrote:
>> On 30 Oct 2014, at 14:42, Leo White <lpw25 at cam.ac.uk> wrote:
>>>> I'm interested in people's thoughts on adding an @inline attribute,
>>>> along the lines of GHC's {-# INLINE #-}:
>>>> 
>>>>  https://www.haskell.org/ghc/docs/7.0.2/html/users_guide/pragmas.html#inline-noinline-pragma
>>>> 
>>>> It'd be useful to have a way of encouraging the compiler to inline
>>>> functions which its own heuristics might discount as too large or
>>>> otherwise too expensive.
>>> I'd like it to go one step further and give a warning or error if
>>> inlining could not be done for some reason (e.g. .cmx file not
>>> present). I think this is very much inline with OCaml's philosophy of
>>> predictable performance -- rather than just hope that the compiler
>>> inlines something I can be certain of it.
>> I agree.  I would also like the reverse mode: a compiler mode that
>> annotates existing source code with @inline attributes where it
>> does actually take place, so that the programmer can get a sense
>> of where it has happened in existing code.
>> 
>> This might better be supported through Merlin or something, but I
>> always liked how ocamlprof rewrote the source code with comments.
>> 
>> Another hopefully simple option that would be handy is a compiler
>> flag that flags a missing .cmx as an error for the purposes of
>> cross-module inlining in ocamlopt, to prevent silently missing
>> inlining opportunities due to build system bugs.
>> 
>> -anil
> It may be quite difficult to do something like that in the general case:
> 
> let f g x =
>  g x
> 
> If f is inlined in different contexts, in some cases g can be inlined in f
> and not in other cases.

Right, but I was thinking specifically of the case where the compiler
finds a .cmxa but not the .cmx, and silently skips cross-module inlining.
If it doesn't do inlining at all then that's fine, but we spent almost
three years silently missing it in Mirage due to OASIS not installing
.cmx files...

-anil