Re: Ada Shootout program for K-Nucleotide (patches)

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Georg Bauhaus <rm.dash-bauhaus@futureapps.de> writes:

> Martin schrieb:
>
>>             .           function Get_Key (E : Element_Access) return
>> Fragment is
>>             .           begin
>> 1,395,255,084              return E.all.Key;
>> 
>> Is there some accessibility check going on in this? Could a 'pragma
>> Assert (E.all /= null);' help?

No, pragma Assert will not help, efficiency-wise.

There is no accessibility check, here.  There's a null check,
which can be suppressed, assuming you "know" it can't fail.

> I'll try this.  Thanks. (-gnatp is on; does it suppress
> accessibility checks, too?)

-gnatp controlls language-defined checks, including the above null
 check.  Pragma Assert is not affected by -gnatp -- pragma Assert
is off by default, and is turned on by -gnata.  If pragma Assert
is turned off, the compiler does not base any optimization decisions on
it -- it's as if it were just erased from the program.

> Hm. Null excluding subtypes...

Yes, I believe adding "not null" will eliminate the above null check in
recent versions of GNAT.  The null check then moves to the call site.
I didn't look at the whole code, but if you're lucky, the call site
will also have "not null" -- the idea is to push the "not null"s as
far as possible, until you get to "new" or "'Access", which obviously
cannot return null.

But if you're using -gnatp, all null checks will be eliminated anyway.

- Bob