[Bug target/108738] compile-time and memory-hog in mdreorg

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108738

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-02-09
     Ever confirmed|0                           |1
      Known to fail|                            |10.4.0
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Happens at least since GCC 10.

There's a comment already:

  /* ???  The following is quadratic since analyze_register_chain
     iterates over all refs to look for dual-mode regs.  Instead this
     should be done separately for all regs mentioned in the chain once.  */
  df_ref ref;
  for (ref = DF_INSN_UID_DEFS (insn_uid); ref; ref = DF_REF_NEXT_LOC (ref))
    if (!HARD_REGISTER_P (DF_REF_REG (ref)))
      analyze_register_chain (candidates, ref);

but the walk also adds to the queue, so it's more interwinded and the suggested
solution isn't the proper.  Instead it might be possible to just record
already visited regs.