[ccache] Support for -fprofile-generate, -fprofile-use, -fprofile-arcs

[Chris AtLee]

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.lebar at 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 <chris at atlee.ca> wrote:
>> On Mon, Aug 8, 2011 at 4:24 PM, Justin Lebar <justin.lebar at 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
>>
>