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From: Dmitry A. Kazakov on 8 Oct 2009 05:11
On Wed, 7 Oct 2009 17:48:56 -0700 (PDT), Yannick Duch�ne Hibou57 wrote:

> I understand what you mean about testing, but I am mainly looking for
> average answers.

The average answer is that any static constraint known to hold must be
specified.

Rationale: this weakens the precondition, which the compiler should
otherwise check dynamically, i.e. possibly generate some additional code.

For non-static constraints the rule is opposite, because it strengthens the
precondition.

So:

in before in out
constant before <nothing>
pool specific before general access

But:

not null vs. <nothing> depends on the where that constraint was put
subtype vs. type, ditto
specific type vs. class, ditto

--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
From: Gautier write-only on 8 Oct 2009 05:38
> I understand what you mean about testing, but I am mainly looking for
> average answers. Just things to know and to have in mind. Even if
> there is no required implementation, it is well known that a lot of
> compilers share some common implementation designs. I'm seeking for
> informations about it, just like the way I'm sometime reading about
> general tips or thoughts (I used to do the same with some prior
> languages like Pascal and Eiffel, it's a bit part of learning the
> thing).

So here is my rule: use only "in" (whenever possible), "in out" and
"out" and you will be happy.
These modes are meaningful for you and the compiler knows how to
handle it efficiently. Especially the compiler will consider passing
by copy, even through a register (and not on the stack), an "in"
parameter:

procedure P_in(i: in Integer; s: in String) is
begin
Put_Line(Integer'Image(i));
Put_Line(s);
end;

-> through GNAT GPL 2008 with -gnatp -O2:

movl %edi, %edx
movl %esi, %ecx
movl $5678, %eax
call _test_in_out__p_in.1893

_________________________________________________________
Gautier's Ada programming -- http://sf.net/users/gdemont/
NB: For a direct answer, e-mail address on the Web site!
From: Gautier write-only on 8 Oct 2009 05:55
> I understand what you mean about testing, but I am mainly looking for
> average answers. Just things to know and to have in mind. Even if
> there is no required implementation, it is well known that a lot of
> compilers share some common implementation designs. I'm seeking for
> informations about it, just like the way I'm sometime reading about
> general tips or thoughts (I used to do the same with some prior
> languages like Pascal and Eiffel, it's a bit part of learning the
> thing).

So here is my rule: use only "in" (whenever possible), "in out" and
"out" and you will be happy.
These modes are meaningful for you and the compiler knows how to
handle it efficiently. Especially the compiler will consider passing
by copy, even through a register (and not on the stack), an "in"
parameter:

procedure P_in(i: in Integer; s: in String) is
begin
Put_Line(Integer'Image(i));
Put_Line(s);
end;

The call P_in(5678,s) is compiled by GNAT GPL 2008 with (-gnatp -O2)
as:

movl %edi, %edx
movl %esi, %ecx
movl $5678, %eax
call _test_in_out__p_in.1893
_________________________________________________________
Gautier's Ada programming -- http://sf.net/users/gdemont/
NB: For a direct answer, e-mail address on the Web site!
From: Yannick Duchêne Hibou57 on 8 Oct 2009 12:04
On 8 oct, 11:55, Gautier write-only <gautier_niou...(a)hotmail.com>
wrote:
> The call P_in(5678,s) is compiled by GNAT GPL 2008 with (-gnatp -O2)
> as:
>
>         movl    %edi, %edx
>         movl    %esi, %ecx
>         movl    $5678, %eax
>         call    _test_in_out__p_in.1893

I was always using the -S option to be passed to GCC, but this was not
building to whole application, so this was not meaningful.

I've just learned the -save-temps is to be used instead : this keep
assembly files *and* build the whole application (providing the
compiler is or is based on GCC)

Otherwise generics does not show anything, this option solve to it.

Do some one have examples from other Ada compilers ? (GNAT is not the
only one).
From: Yannick Duchêne Hibou57 on 8 Oct 2009 12:46
There is also an option named -fverbose-asm which leaves more
informations in the assembly, like some variable names and other more
or less readable stuff, but seemingly no source line numbers. This
help to see interesting things.
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