Re: GNAT not generating any code for sub‑program: known bug?

["Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr>]

Le Sun, 28 Apr 2013 00:22:41 +0200, Yannick Duchêne (Hibou57)  
<yannick_duchene@yahoo.fr> a écrit:

> Le Sat, 27 Apr 2013 23:08:52 +0200, Yannick Duchêne (Hibou57)  
> <yannick_duchene@yahoo.fr> a écrit:
>
>> Hi all,
>>
>> I will make a stripped‑down version of the case, later.
>
> Here is:
> http://www.les-ziboux.rasama.org/download/2013-04-28-cla-gnat-bug.zip
>
> The bug disappears when optimization is disabled or else when the  
> sub‑program is made inlinable.

Seems there is an issue with sub‑program using Ada's machine‑code  
insertion.

If the sub‑program which contains machine‑code insertion is not inlined,  
then the machine‑code insertion part gets dropped by compiler  
optimization, which so seems to be more a GCC bug than a GNAT bug. The  
sub‑programs invoke this sub‑program either directly or indirectly, also  
has to all be inlined too.

There is a work‑around: implement the sub‑program using machine‑code  
insertion as a generic, say `GP`. Then implement `P` which use an  
instantiation of `GP` internally, and it will works. `GP` cannot be  
declared inlined, or else you will get a GNAT bug‑box. However, if `P`  
declared inlined, then its containing `GP` instantiation will be properly  
inlined. `P` will be generated when it's either inlined or not  
(effectively workaround the bug), and will be really fully inline if  
declared inlined (no efficiency cost).

Template as a summary:

     generic
        …
     procedure/function GP (…);
     -- No `Inline` here! either `True` or `False`,
     -- or else GNAT says “kaboom”.

     procedure/function GP (…) is
     begin
       -- Machine code insertion here
     end;

     procedure/function P (…)
        [with Inline => True/False];
        -- Works with either of the three.

     procedure/function P (…) is
         procedure/function Implementation is
            new GP (…);
     begin
         [return] Implementation (…);
     end;


-- 
“Syntactic sugar causes cancer of the semi-colons.” [1]
“Structured Programming supports the law of the excluded muddle.” [1]
[1]: Epigrams on Programming — Alan J. — P. Yale University