Re: Profiling Ada binaries

["Markus Schöpflin" <no.spam@spam.spam>]

Am 25.07.2016 um 18:45 schrieb rieachus@comcast.net:

> Gee. I would never think to compile the math libraries with -O1.
> Seriously, the math libraries are written with ease of understanding in
> mind.  You may have thousands of calls in the implementation of one
> function, and due to the packages being generic, every one of those calls
> will do an elaboration check.  How can that be efficient?

GNAT by default uses static elaboration. There should be no elaboration checks 
when calling the generic versions. Or am I mistaken here?

 > I believe GNAT
> has non-generic versions for Short_Float, Float, and Long_Float which use
> the hardware built-ins.  But I doubt you would get that automatically with
> -O1.

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

> Try compiling everything with -O3 (or whatever you use) then recompile only
> the unit you want the tracing for with -O1 and -fno-inline-functions-called-once.

-O3 is explicitly discouraged by the documentation, so we're normally using 
-O2. And to get a general feeling on where the application is burning its CPU 
cycles, -O1 seems to be OK, as the execution time normally is dominated by the 
choice of algorithms and not by differences in the optimization level.

Markus