Re: [Caml-list] Status of Flambda in OCaml 4.03

[Alain Frisch <alain.frisch@lexifi.com>]

Hi Markus,

flambda needs to be enabled explicitly at configure time with the 
"-flambda" flag.  The new optimizer will then be used unconditionally, 
and you can tweak it using command-line parameters passed to ocamlopt 
(see "ocamlopt -h").


Alain

On 08/03/2016 23:10, Markus Mottl wrote:
> Hi,
>
> I'm trying out OCaml 4.03.0+beta1 right now and wanted to test Flambda
> optimizations.  But looking at the generated assembly, it doesn't seem
> to be doing much if anything on the simple test examples that I
> thought would benefit.
>
> To give an example of what I expected to see, lets consider this code:
>
> -----
> let map_pair f (x, y) = f x, f y
>
> let succ x = x + 1
> let map_pair_succ1 pair = map_pair succ pair
> let map_pair_succ2 (x, y) = succ x, succ y
> -----
>
> I would have thought that the "succ" function would be inlined in
> "map_pair_succ1" as the compiler would do for "map_pair_succ2".
> But the generated code looks like this:
>
> -----
> L101:
>    movq  %rax, %rdi
>    movq  %rdi, 8(%rsp)
>    movq  %rbx, (%rsp)
>    movq  8(%rbx), %rax
>    movq  (%rdi), %rsi
>    movq  %rdi, %rbx
>    call  *%rsi
> L102:
>    movq  %rax, 16(%rsp)
>    movq  (%rsp), %rax
>    movq  (%rax), %rax
>    movq  8(%rsp), %rbx
>    movq  (%rbx), %rdi
>    call  *%rdi
> -----
>
> Is Flambda supposed to work out of the box with the current beta?
> What flags or annotations should I use for testing?  Any showcase
> examples I should try out that are expected to be improved?
>
> Regards,
> Markus
>