[Bug rtl-optimization/59811] [4.9/5/6 Regression] Huge increase in memory usage and compile time in combine

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59811

--- Comment #15 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note that the wide-int merge brought some extra slowness into
get_ref_base_and_extent which is no longer call free.  For example

        case BIT_FIELD_REF:
          bit_offset += wi::to_offset (TREE_OPERAND (exp, 2));
          break;

is optimized to

<L24>:
  _68 = exp_403->exp.operands[2];
  MEM[(struct  &)&D.86120] ={v} {CLOBBER};
  _445 = MEM[(unsigned int *)&bit_offset + 24B];
  _448 = MEM[(const union tree_node *)_68].base.u.int_length.offset;
  _449 = (unsigned int) _448;
  _451 = _445 + _449;
  if (_451 == 2)
    goto <bb 31>;
  else
    goto <bb 32>;

  <bb 31>:
  _455 = MEM[(const long int *)&bit_offset];
  _456 = (long unsigned int) _455;
  _457 = MEM[(const long int *)_68 + 16B];
  _458 = (long unsigned int) _457;
  resultl_459 = _456 + _458;
  resultl.194_460 = (long int) resultl_459;
  MEM[(long int *)&D.86120] = resultl.194_460;
  _1156 = resultl.194_460 >= 0;
  _896 = (long int) _1156;
  _895 = -_896;
  MEM[(long int *)&D.86120 + 8B] = _895;
  _462 = _456 ^ resultl_459;
  _463 = _458 ^ resultl_459;
  _464 = _462 & _463;
  _465 = _464 >> 63;
  _466 = (unsigned int) _465;
  _467 = _466 + 1;
  MEM[(struct fixed_wide_int_storage *)&D.86120].len = _467;
  goto <bb 33>;

  <bb 32>:
  _450 = &MEM[(const union tree_node *)_68].int_cst.val[0];
  _468 = wi::add_large (&MEM[(struct fixed_wide_int_storage *)&D.86120].val,
&MEM[(const struct fixed_wide_int_storage *)&bit_offset].val, _445, _450, _449,
128, 1, 0B);
  MEM[(struct fixed_wide_int_storage *)&D.86120].len = _468;

  <bb 33>:
  MEM[(struct generic_wide_int *)&bit_offset] = MEM[(struct generic_wide_int
*)&D.86120];
  D.86120 ={v} {CLOBBER};
  pretmp_580 = exp_403->exp.operands[0];
  goto <bb 119>;

while it was a simple

<L21>:
  _64 = exp_1->exp.operands[2];
  SR.212_245 = MEM[(struct double_int *)_64 + 16B];
  SR.213_244 = MEM[(struct double_int *)_64 + 24B];
  MEM[(struct double_int *)&D.52195] = SR.212_245;
  MEM[(struct double_int *)&D.52195 + 8B] = SR.213_244;
  double_int::operator+= (&bit_offset, D.52195);
  pretmp_295 = exp_1->exp.operands[0];
  goto <bb 70>;

in GCC 4.9 (ok, looks like double_int::operator+= wasn't inlined there
either).

That said, more detailed profiling is needed here but get_ref_base_and_extent
is one of the bottle-necks here.