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

[Clemens Eisserer]

Hi,

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?

Thank you in advance, Clemens Eisserer