Ah ha! What does this mean for whether it's worthwhile to include the .gcda contents in the hash when using -fprofile-use, and therefore if it's worthwhile to cache -fprofile-use at all?
On Wed, Aug 10, 2011 at 11:03 AM, Justin Lebar <justin.le...@gmail.com> wrote: > gcda files are cumulative. Try > > $ ./test; md5sum test.gcda; rm test.gcda > hello world > 1c14199a60b2e5b9e6f1e96360adc40c test.gcda > $ ./test; md5sum test.gcda; rm test.gcda > hello world > 1c14199a60b2e5b9e6f1e96360adc40c test.gcda > > On Wed, Aug 10, 2011 at 10:51 AM, Chris AtLee <ch...@atlee.ca> wrote: >> On Mon, Aug 8, 2011 at 4:24 PM, Justin Lebar <justin.le...@gmail.com> wrote: >>>> The .gcda files themselves aren't cached, their contents are used to >>>> calculate the hash for a -fprofile-use run. So if the .o file doesn't >>>> exist, and you have the same .gcda file, you get a cache hit. >>> >>> Ah, I see. What if the .o file does exist? Why should that matter, >>> if gcc is going to overwrite it anyway? >> >> It doesn't really matter..my point was that hopefully your make >> dependencies are set up so you're not calling gcc if you don't need >> to. >> >>> You mentioned earlier that a simple program without branches or loops >>> didn't generate the same .gcda files when the program was run twice. >>> Would you mind including that code? I wrote a pretty simple testcase >>> and observed the opposite result. Maybe it's different in different >>> versions of gcc or something. >> >> I have a simple hello world program. Even if I comment out the printf >> I get different .gcda files after each run. >> >> #include <stdio.h> >> >> int main() { >> printf("hello world\n"); >> return 0; >> } >> >> gcc -fprofile-generate -c -o test.o test.c >> gcc -fprofile-generate test.o -o test >> ./test; md5sum test.gcda >> 83fdede120951b154184271416082bdb test.gcda >> ./test; md5sum test.gcda >> 230d10c340e6ae068a7d65b4bc355472 test.gcda >> > _______________________________________________ ccache mailing list ccache@lists.samba.org https://lists.samba.org/mailman/listinfo/ccache