[Bug gcov-profile/54487] [4.8 Regression] profiledbootstrap broken by r190952

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54487

--- Comment #8 from Teresa Johnson <tejohnson at google dot com> 2012-09-06 18:58:55 UTC ---
I think I have a solution for the issue that H.J. is encountering. Details
below. Markus and H.J., would you be able to try the following patch to see if
it addresses the failure you were seeing? Markus, were you only seeing failures
when using a parallel make?

Index: libgcc/libgcov.c
===================================================================
--- libgcc/libgcov.c    (revision 191035)
+++ libgcc/libgcov.c    (working copy)
@@ -707,7 +707,9 @@ gcov_exit (void)
         memcpy (cs_all, cs_prg, sizeof (*cs_all));
       else if (!all_prg.checksum
            && (!GCOV_LOCKED || cs_all->runs == cs_prg->runs)
-           && memcmp (cs_all, cs_prg, sizeof (*cs_all)))
+                   && memcmp (cs_all, cs_prg,
+                              sizeof (*cs_all) - (sizeof (gcov_bucket_type)
+                                                  * GCOV_HISTOGRAM_SIZE)))
         {
           fprintf (stderr, "profiling:%s:Invocation mismatch - some data files
may have been removed%s\n",
                gi_filename, GCOV_LOCKED


After looking at the cp-demangle matching issue for awhile, I finally realized
that in my case at least, it was a valid issue with the preprocessed
cp-demangle source code not matching the existing cp-demangle.gcda file. I
tracked that down to different includes being done due to a difference in the
libiberty configure. The libiberty config.log showed that there were some
failures in some of the checks which were using the instrumented prev-gcc/xgcc
that was giving errors like:

profiling:/home/tejohnson/extra/gcc_trunk_4_validate4/gcc/dwarf2out.gcda:Invocation
mismatch - some data files may have been removed
configure:3427: $? = 0
configure: failed program was:
...

When profile merging happens, there are some sanity checks to ensure that the
merged summaries for all object files are the same. These tests are failing in
some cases due to small differences in the merged histograms, resulting in the
above message. The total of the counter values in the histogram is the same,
but there are slight differences in the cumulative counter values assigned to
consecutive buckets. This could happen due to the way the cumulative counter
values are apportioned out to the counters when merging. If the summaries are
merged in different orders by the parallel runs, the integer division
truncation may result in small differences. Ultimately these differences don't
matter much as the sum of all the counter values saved in the histograms is
consistent and the differences will be small and not significant. 

The best solution is to ignore the histogram when doing the sanity check, and
just compare the high-level summary info (sum_all, sum_max, run_max, etc). That
seems to be addressing the issue I was having. At least, I haven't been able to
reproduce it yet.