[Bug rtl-optimization/105559] [12/13 Regression] -g and -O3 cause timeout since r12-156-g8d4c374c4419a875

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105559

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |compile-time-hog
          Component|c                           |rtl-optimization

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
stuck in RTL jump pass btw, calling delete_trivially_dead_insns at the start
of its invocation (_not_ during the jump threading iteration).

We have a block with very many DEBUG_INSN at end and delete_insn_and_edges
does

/* Like delete_insn but also purge dead edges from BB.
   Return true if any edges are eliminated.  */

bool
delete_insn_and_edges (rtx_insn *insn)
{
  bool purge = false;

  if (INSN_P (insn) && BLOCK_FOR_INSN (insn))
    {
      basic_block bb = BLOCK_FOR_INSN (insn);
      if (BB_END (bb) == insn)
        purge = true;
      else if (DEBUG_INSN_P (BB_END (bb)))
        for (rtx_insn *dinsn = NEXT_INSN (insn);
             DEBUG_INSN_P (dinsn); dinsn = NEXT_INSN (dinsn))
          if (BB_END (bb) == dinsn)
            {
              purge = true;
              break;
            }
    }
  delete_insn (insn);
  if (purge)
    return purge_dead_edges (BLOCK_FOR_INSN (insn));

that's highly inefficient when insn is a debug insn itself.  Fixing that
alone doesn't seem to be enough to make it "fast" but at least it
finishes in 20s for me then with no obvious peak.