Re: Profiling Ada binaries

["Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>]

On 08/01/2016 03:40 PM, rieachus@comcast.net wrote:
> On Tuesday, July 26, 2016 at 4:37:31 AM UTC-4, Markus Schöpflin wrote:
>  
> 
>> Even using the non-generic versions I have not been able to get the hardware 
>> built-ins. The best I can achieve for a call to e.g. cos(X) is: 
> 
>>         call    ada__numerics__long_elementary_functions__cos
> 
> Again GNAT docs to the rescue: 15.1 Machine code insertions:

I think the OP would benefit from knowing why this is necessary.

If you look at the body of Ada.Numerics.Long_Elementary_Functions.Cos, you'll
probably find a call to {something that calls} the built-in function.

If you look at the requirements for the Cos function in Annex A and Annex G (if
implemented, which it is for GNAT), you'll find a number of requirements for
accuracy and special cases. If you look at the definition of the built-in
function, you'll likely find that it doesn't meet all of those requirements. Any
call to Cos has to involve wrapping a call to the built-in function in code to
ensure those requirements are met, so you won't find a call to the built-in
function in the generated code.

Even if the built-in function met all the requirements, the desire for the
compiler to be portable will result in the call to the built-in being squirreled
away, not produced by the code generator.

The general rule, "If you need specific machine code, use a machine-code
insertion," applies here. Of course, the result is non-portable code, while the
call to the language-defined library function is portable.

-- 
Jeff Carter
"Hello! Smelly English K...niggets."
Monty Python & the Holy Grail
08