What kind of data is collected with -fprofile-generate?

[Clemens Eisserer]

Hi Ian,

> The profiling information collects execution counts.  The size scales
> with the number of branches in your program.  It does not scale with the
> amount of data nor how long the program runs.
Thanks a lot for explaining.
The results profile-driven optimizations yield are really impressive :)

- Clemens


2009/7/24 Ian Lance Taylor <iant@google.com>:
> Clemens Eisserer <linuxhippy@gmail.com> writes:
>
>> I've been playing with profile driven optimizations lately and it
>> seems to work really well :)
>> Even with -mtune=generic I am able to get a 20% time reduction for a
>> critical piece of code.
>>
>> What I wonder however is, how the profiling informations are collected.
>>
>> E.g. when profiling pixman, I feed about 1Mio trapezoids to it,
>> however gcc only collects  ~1.5kb profile information for that Object
>> file:
>>> -rw-rw-r-- 1 ce ce  1784 2009-07-24 15:22 libpixman_1_la-pixman-trap.gcda
>>
>> It seems irrelevant how much test-data I feed duing the profiling
>> stage, it won't grow beyond that 1.7kb.
>>
>> Any ideas why?
>

>
> Ian
>