https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81192
--- Comment #7 from Tom de Vries <vries at gcc dot gnu.org> ---
I used dotfn (based on dot-fn in gdbhooks.py):
...
void
dotfn (const char *name)
{
FILE *fp = fopen (name, "w");
if (fp == NULL)
return;
start_graph_dump (fp, "<debug>");
print_graph_cfg (fp, cfun, dump_flags);
end_graph_dump (fp);
fclose (fp);
}
...
to debug this test-case and found that the sigsegv goes away when I use dotfn
before init_worklist.
As it turns out, draw_cfg_edges calls mark_dfs_back_edges, which sets
EDGE_DFS_BACK for bb4 -> bb5. Consequently, the outgoing edges of bb4 and bb6
don't have the same flags any more, and tail-merge bails out.
