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

[Markus Mottl <markus.mottl@gmail.com>]

Hi Alain,

I see, thanks.  It was a little confusing, because the command line
options for tuning flambda were still available even without Flambda
being enabled.

Will Flambda be enabled by default in OCaml 4.03 or is it still
considered to be too experimental?  It could turn out to become one of
the most impactful new features in terms of how I write code.

Regards,
Markus

On Tue, Mar 8, 2016 at 5:53 PM, Alain Frisch <alain.frisch@lexifi.com> wrote:
> 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
>>
>



-- 
Markus Mottl        http://www.ocaml.info        markus.mottl@gmail.com