-fprofile-generate and multiple runs

[Martin Mitáš]

Hi.

I'm working on a shared lib which I would like to optimize
with profile guided optimization. I would prefer to have
multiple small programs (one for typical use case), each
examining a single module of the lib rather then one big
program covering complete lib's API, and to generate the
profile by running all those use cases.

When built with -fprofile-generate, and the resulted binary
is executed multiple times, are the .gcda files (re)written
from scratch every time, or are they updated so they contain
a combined profile data from multiple runs?

Any other gotchas this approach might bring?

gcc manual does not provide any details about this...

Thanks in advance,
Mity