[Bug lto/66229] New: LTO fails with -fauto-profile on mcf

["spop at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66229

            Bug ID: 66229
           Summary: LTO fails with -fauto-profile on mcf
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
          Assignee: hubicka at gcc dot gnu.org
          Reporter: spop at gcc dot gnu.org
                CC: dehao at gcc dot gnu.org, hiraditya at msn dot com
  Target Milestone: ---

lto1: internal compiler error: in compute_working_sets, at gcov-io.c:1006
0x790dad compute_working_sets(gcov_ctr_summary const*, gcov_working_set_info*)
        ../../gcc/gcov-io.c:1006
0xba0faa get_working_sets()
        ../../gcc/profile.c:264
0xaf0ac7 input_symtab()
        ../../gcc/lto-cgraph.c:1880
0x6c3da0 read_cgraph_and_symbols
        ../../gcc/lto/lto.c:3061
0x6c4be9 lto_main()
        ../../gcc/lto/lto.c:3479


MCF from SPEC 2006 on x86_64-linux and other programs would fail with LTO +
AutoFDO with the following flags:
COPTIMIZE   = -Ofast -g3 -fno-strict-aliasing -flto
-fauto-profile=mcf_base.gcc43-64bit.gcov

This fails with both trunk gcc and with the 5.1 release.
Also fails with an empty profile.
We collected the profile with create_gcov from a linux perf data.

We ran gdb on lto1 and have seen that the crash happens in gcov reader of lto:
gcc/gcov-io.c:1006

/* Compute the working set information from the counter histogram in
   the profile summary. This is an array of information corresponding to a
   range of percentages of the total execution count (sum_all), and includes
   the number of counters required to cover that working set percentage and
   the minimum counter value in that working set.  */

GCOV_LINKAGE void
compute_working_sets (const struct gcov_ctr_summary *summary,
                      gcov_working_set_t *gcov_working_sets)
{
[...]
  /* Next, walk through the histogram in decending order of hotness
     and compute the statistics for the working set summary array.
     As histogram entries are accumulated, we check to see which
     working set entries have had their expected cum_value reached
     and fill them in, walking the working set entries in increasing
     size of cum_value.  */
  ws_ix = 0; /* The current entry into the working set array.  */
  cum = 0; /* The current accumulated counter sum.  */
  count = 0; /* The current accumulated count of block counters.  */
  for (h_ix = GCOV_HISTOGRAM_SIZE - 1;
       h_ix >= 0 && ws_ix < NUM_GCOV_WORKING_SETS; h_ix--)
    {
      histo_bucket = &summary->histogram[h_ix];

      /* If we haven't reached the required cumulative counter value for
         the current working set percentage, simply accumulate this histogram
         entry into the running sums and continue to the next histogram
         entry.  */
      if (cum + histo_bucket->cum_value < working_set_cum_values[ws_ix])
        {
          cum += histo_bucket->cum_value;
          count += histo_bucket->num_counters;
          continue;
        }

[Here continue is always taken such that ws_ix never gets incremented.]
[...]
    }
  gcov_nonruntime_assert (ws_ix == NUM_GCOV_WORKING_SETS);

[And this would assert because ws_ix is still 0.]