How to properly use -fprofile-use

[Frederic Chardon]

Hello the list,
I'm using dosbox to run an old game and as for all emulators, the CPU
ressources needed are quite high. After playing with dosbox
configuration there are almost no slowdowns anymore (yipee). So to
remove the last few lag I started to look into gcc flags and in
particular profiling which seems just great to optimize speed for one
specific port. I deactivated ccache since it mess with the .gcda files
creation, and after adding -fprofile-generate to CFLAGS and recompile
it runs awfully slowly and a bunch of .gcda and .gcno are created in
the work directory. So I believe this part works as it should.
The problem is when I later recompile: replace -fprofile-generate by
-fprofile-use then make -DFORCE_PKG_REGISTER install clean, the first
thing make do is... delete the .gcda (but not the .gcno). Quite
annoying isn't it? I then have a lot of warning complaining about
"xxx.gcda not found".
My question is, how should I do to correctly use profiling for a port?
In src.conf (I use RELENG_7) I have WITHOUT_PROFILE, does it have any
influence?
Best regards
Frederic