[Bug rtl-optimization/98863] WRF with LTO consumes a lot of memory in split2 pass

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98863

--- Comment #12 from Richard Biener <rguenth at gcc dot gnu.org> ---
Wow, so the MIR problem starts with

static void
df_mir_alloc (bitmap all_blocks)
{   
...
  EXECUTE_IF_SET_IN_BITMAP (all_blocks, 0, bb_index, bi)
    {
...
          bitmap_set_range (&bb_info->in, 0, DF_REG_SIZE (df));
          bitmap_set_range (&bb_info->out, 0, DF_REG_SIZE (df));

I'll see if I can apply the same trick I applied to tree PRE when it
had its "maximum set".