[Bug bootstrap/55051] [4.8 Regression] profiledbootstrap failed

["tejohnson at google dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55051

--- Comment #25 from Teresa Johnson <tejohnson at google dot com> 2012-11-15 14:34:10 UTC ---
On Thu, Nov 15, 2012 at 2:56 AM, hubicka at ucw dot cz <
gcc-bugzilla@gcc.gnu.org> wrote:

>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55051
>
> --- Comment #24 from Jan Hubicka <hubicka at ucw dot cz> 2012-11-15
> 10:56:53 UTC ---
> > Note though that this is not an assert. It just emits a message to
> > stderr. Do you think a better error message is appropriate? I'm not
> > sure the "some data files may have been removed" is an accurate
> > description of the issue. Perhaps something like "Profile data file
> > mismatch may indicate corrupt profile data"?
>
> Well, we should figure out why sum_all starts to diverge.  If we had
> problems mixing cc1 and cc1plus executions, we should get mismatches in
> number of counters.


Right, it doesn't appear to be different executables since the number of
counters is identical. I'll instrument it and see if I can figure out why
they diverge.


> What happens after the miscompare?
>

A flag is set so that the error is emitted at most once per merge, and then
we continue on with the merge and ignore it. Basically what it is doing is
saving the first merged summary (for the first object file's gcda we merge
into), and then for each additional object file that gets its counters
merged the resulting program summary is compared against the saved program
summary. But only if the number of runs is the same as the saved summary.
This could happen if the gcda files are walked in a different order during
updates (i.e. the gcov_list is in a different order for different processes
of the same executable), but I am not sure if that can happen.

Teresa


> Honza
>
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