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From: "aldyh at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/109154] [13 regression] jump threading
 de-optimizes nested floating point comparisons
Date: Wed, 22 Mar 2023 10:20:53 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109154

Aldy Hernandez <aldyh at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amacleod at redhat dot com,
                   |                            |law at gcc dot gnu.org,
                   |                            |rguenth at gcc dot gnu.org

--- Comment #4 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
(In reply to Tamar Christina from comment #3)
> Aldy, any thoughts here?

We need a "real" threading expert on this one, as the decision by ranger is
correct.  It looks like this is a profitability issue in the threader.

The problem can be seen with -O2 --param=3Dthreader-debug=3Dall, on the thr=
eadfull1
dump:

The threaded path is:
path: 4->5->7 SUCCESS

ranger can fold the conditional in BB5:

    if (_1 < 1.0e+0)
      goto <bb 7>; [41.00%]
    else
      goto <bb 6>; [59.00%]

...because on entry to BB5 we know _1 < 0.0:

  <bb 3> [local count: 955630225]:
  _1 =3D (float) l_9;
  _2 =3D _1 < 0.0;
  zone1_15 =3D (int) _2;
  if (_1 < 0.0)
    goto <bb 4>; [41.00%]
  else
    goto <bb 5>; [59.00%]

  <bb 4> [local count: 391808389]:

  <bb 5> [local count: 955630225]:
  # iftmp.0_10 =3D PHI <zone1_15(4), 1(3)>
  fasten_main_natpro_chrg_init.2_3 =3D fasten_main_natpro_chrg_init;
  _4 =3D fasten_main_natpro_chrg_init.2_3 * iftmp.0_10;
  _5 =3D (float) _4;
  if (_1 < 1.0e+0)
    goto <bb 7>; [41.00%]
  else
    goto <bb 6>; [59.00%]

If this shouldn't be threaded because of a hot/cold issue, perhaps the code
goes in back_threader_profitability::profitable_path_p() where there's alre=
ady
logic wrt hot blocks.=