Bug (segmentation fault) in the generation of counterexamples

Hello,

I believe there is a bug in the code that generates counterexamples. I am using Bison to generate parser from some proprietary grammar and it is running normally and generating desired output in regular case. But when I want to generate debug information with command line options " --report=counterexamples --report-file=out.txt" then Bison terminates with segmentation fault. I have built debug version of Bison 3.7.4 (I have passed CFLAGS="-ggdb3 -O0" CXXFLAGS="-ggdb3 -O0" LDFLAGS="-ggdb3" into Bison's configure) and generated core file which I am attaching to this e-mail. 

Running Bison under gdb also points that the segmentation fault might be related to generation of counterexamples report:

Program received signal SIGSEGV, Segmentation fault.
0x0000555555578631 in eligible_state_items (target=0x7ffff74bd500) at src/lssi.c:140
140	      BITSET_FOR_EACH (biter, rsi, sin, 0)
(gdb) bt
#0  0x0000555555578631 in eligible_state_items (target=0x7ffff74bd500) at src/lssi.c:140
#1  0x0000555555578721 in shortest_path_from_start (target=965, next_sym=11) at src/lssi.c:155
#2  0x00005555555678b3 in counterexample_report (itm1=965, itm2=968, next_sym=11, shift_reduce=false, out=0x5555558151b0, prefix=0x5555555e55f2 "    ") at src/counterexample.c:1240
#3  0x000055555556813c in counterexample_report_reduce_reduce (itm1=965, itm2=968, conflict_syms=0x5555557e6bb0, out=0x5555558151b0, prefix=0x5555555e55f2 "    ") at src/counterexample.c:1335
#4  0x0000555555568491 in counterexample_report_state (s=0x5555557cec20, out=0x5555558151b0, prefix=0x5555555e55f2 "    ") at src/counterexample.c:1379
#5  0x000055555559a6ee in print_state (out=0x5555558151b0, s=0x5555557cec20) at src/print.c:364
#6  0x000055555559ad47 in print_results () at src/print.c:471
#7  0x0000555555579756 in main (argc=7, argv=0x7fffffffe1b8) at src/main.c:178

I hope that it would be possible to debug the problem with attached core file. If not, please let me know and I will try to provide more information about the grammar (some minimal example) I am using to generate the problem.

Best regards,
Michal Bartkowiak