[Bug middle-end/83019] New: Compiler dumps predictions with -nan%

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83019

            Bug ID: 83019
           Summary: Compiler dumps predictions with -nan%
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ubizjak at gmail dot com
  Target Milestone: ---

Recent patch caused some dumps to dump -nam%.

One example is gcc.dg/graphite/interchange-12.c, which generates:

./cc1 -O2 -ffast-math -floop-nest-optimize -fdump-tree-graphite-all
interchange-12.c

interchange-12.c.150t.graphite:

...
Predictions for bb 29
  first match heuristics: 99.0%  exec 0 (estimated locally) hit 0 (estimated
locally) (-nan%)
  combined heuristics: 99.0%  exec 0 (estimated locally) hit 0 (estimated
locally) (-nan%)
  loop iterations heuristics of edge 29->28: 1.0%  exec 0 (estimated locally)
hit 0 (estimated locally) (-nan%)
Predictions for bb 30
1 edges in bb 30 predicted to even probabilities
Predictions for bb 28
  first match heuristics: 99.0%  exec 0 (estimated locally) hit 0 (estimated
locally) (-nan%)
  combined heuristics: 99.0%  exec 0 (estimated locally) hit 0 (estimated
locally) (-nan%)
  loop iterations heuristics of edge 28->22: 1.0%  exec 0 (estimated locally)
hit 0 (estimated locally) (-nan%)
...

The above dump was generated with x86_64-linux-gnu host. This is problematic
with hosts (e.g. alpha) that require -mieee when dealing with NaNs, resulting
in several ICEs [1].

The cause is the division 0/0 in:

Program received signal SIGFPE, Arithmetic exception.
0x00000001207a4ee4 in dump_prediction (file=0x121665bf0, predictor=<optimized
out>, probability=<optimized out>, bb=0x2000099df48, reason=<optimized o
ut>, 
    ep_edge=<optimized out>) at
/space/homedirs/uros/gcc-svn/trunk/gcc/predict.c:750
750               fprintf (file, " (%.1f%%)", e->count ().to_gcov_type() *
100.0
(gdb) bt
#0  0x00000001207a4ee4 in dump_prediction (file=0x121665bf0,
predictor=<optimized out>, probability=<optimized out>, bb=0x2000099df48, 
    reason=<optimized out>, ep_edge=<optimized out>) at
/space/homedirs/uros/gcc-svn/trunk/gcc/predict.c:750
#1  0x00000001207af424 in combine_predictions_for_bb (bb=0x2000099df48,
dry_run=<optimized out>) at /space/homedirs/uros/gcc-svn/trunk/gcc/predict.c:1
270
#2  0x00000001207b23d0 in tree_estimate_probability (dry_run=<optimized out>)
at /space/homedirs/uros/gcc-svn/trunk/gcc/predict.c:2819
#3  0x0000000120f6bf24 in graphite_transform_loops () at
/space/homedirs/uros/gcc-svn/trunk/gcc/graphite.c:425
#4  0x0000000120f6d374 in graphite_transforms (fun=0x12120fc31) at
/space/homedirs/uros/gcc-svn/trunk/gcc/graphite.c:447
#5  (anonymous namespace)::pass_graphite_transforms::execute (this=0x121665bf0,
fun=0x12120fc31) at /space/homedirs/uros/gcc-svn/trunk/gcc/graphite.c:
524
#6  0x000000012078b038 in execute_one_pass (pass=0x1214fe7c0) at
/space/homedirs/uros/gcc-svn/trunk/gcc/passes.c:2497
#7  0x000000012078bc08 in execute_pass_list_1 (pass=0x1214fe7c0) at
/space/homedirs/uros/gcc-svn/trunk/gcc/passes.c:2586
#8  0x000000012078bc24 in execute_pass_list_1 (pass=0x1214fe760) at
/space/homedirs/uros/gcc-svn/trunk/gcc/passes.c:2587
#9  0x000000012078bc24 in execute_pass_list_1 (pass=0x1214fe400) at
/space/homedirs/uros/gcc-svn/trunk/gcc/passes.c:2587
#10 0x000000012078bc24 in execute_pass_list_1 (pass=0x1214fd070) at
/space/homedirs/uros/gcc-svn/trunk/gcc/passes.c:2587
#11 0x000000012078bca4 in execute_pass_list (fn=<optimized out>,
pass=0x12120fc31) at /space/homedirs/uros/gcc-svn/trunk/gcc/passes.c:2597
#12 0x0000000120363804 in cgraph_node::expand (this=0x200009c8000) at
/space/homedirs/uros/gcc-svn/trunk/gcc/cgraphunit.c:2139
#13 0x00000001203652a0 in expand_all_functions () at
/space/homedirs/uros/gcc-svn/trunk/gcc/cgraphunit.c:2275
#14 symbol_table::compile (this=<optimized out>) at
/space/homedirs/uros/gcc-svn/trunk/gcc/cgraphunit.c:2623
#15 0x000000012036874c in compile (this=0x200008a4000) at
/space/homedirs/uros/gcc-svn/trunk/gcc/cgraphunit.c:2682
#16 symbol_table::finalize_compilation_unit (this=0x200008a4000) at
/space/homedirs/uros/gcc-svn/trunk/gcc/cgraphunit.c:2716
#17 0x00000001208a695c in compile_file () at
/space/homedirs/uros/gcc-svn/trunk/gcc/toplev.c:480
#18 0x000000012013ae90 in do_compile () at
/space/homedirs/uros/gcc-svn/trunk/gcc/toplev.c:2060
#19 toplev::main (this=0x11fdff040, argc=<optimized out>, argv=<optimized out>)
at /space/homedirs/uros/gcc-svn/trunk/gcc/toplev.c:2195
#20 0x000000012013cf60 in main (argc=<optimized out>, argv=0x11fdff168) at
/space/homedirs/uros/gcc-svn/trunk/gcc/main.c:39
(gdb) list
745           bb->count.dump (file);
746           if (e)
747             {
748               fprintf (file, " hit ");
749               e->count ().dump (file);
750               fprintf (file, " (%.1f%%)", e->count ().to_gcov_type() *
100.0
751                        / bb->count.to_gcov_type ());
752             }
753         }
754

[1] https://gcc.gnu.org/ml/gcc-testresults/2017-11/msg01330.html