[Bug middle-end/93092] g++ takes tremendous compilation times in var-tracking

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93092

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
On trunk:

(gdb) p cfun->cfg->x_last_basic_block 
$1 = 8940
(gdb) p cfun->cfg->x_n_edges
$2 = 14897

so we miss

  if (n_basic_blocks_for_fn (cfun) > 500
      && n_edges_for_fn (cfun) / n_basic_blocks_for_fn (cfun) >= 20)
    {
      vt_debug_insns_local (true);
      return 0;
    }

this isn't really a good absolute limit, it's just singling out very
insane cases of very many edges (but allow scaling with the number of BBs).

There's another limit for the dataflow problem size that is also not hit
(--param max-vartrack-size).

There are plenty of similar bugreports (unfortunately).