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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/110963] [14 Regression] Dead Code Elimination
 Regression since r14-2946-g46c8c225455
Date: Wed, 09 Aug 2023 19:52:59 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: pinskia at gcc dot gnu.org
X-Bugzilla-Status: NEW
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X-Bugzilla-Priority: P3
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X-Bugzilla-Target-Milestone: 14.0
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X-Bugzilla-Changed-Fields: cf_reconfirmed_on bug_status everconfirmed
Message-ID: <bug-110963-4-naC9x1sOKA@http.gcc.gnu.org/bugzilla/>
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110963

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-08-09
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.
PRE seems to have missed an obvious redundant load here though:
The IR after PRE:
```
  pretmp_12 =3D h;
  if (f.2_9 !=3D 0)
    goto <bb 3>; [50.00%]
  else
    goto <bb 6>; [50.00%]
...
  <bb 6> [local count: 536870912]:
  if (pretmp_12 =3D=3D 0B)
    goto <bb 8>; [30.00%]
  else
    goto <bb 7>; [70.00%]

  <bb 7> [local count: 375809640]:
  h =3D 0B;

  <bb 8> [local count: 536870912]:
  g =3D 0;
  h.6_15 =3D h;
```

The IR before PRE:
```
  <bb 2> [local count: 1073741824]:
  # VUSE <.MEM_2(D)>
  f.2_9 =3D f;
  if (f.2_9 !=3D 0)
    goto <bb 3>; [50.00%]
  else
    goto <bb 5>; [50.00%]

  <bb 3> [local count: 536870912]:
  # VUSE <.MEM_2(D)>
  _11 =3D h;
  if (_11 !=3D 0B)
    goto <bb 4>; [0.00%]
  else
    goto <bb 9>; [100.00%]
...
  <bb 5> [local count: 536870912]:
  # VUSE <.MEM_2(D)>
  _13 =3D h;
  if (_13 =3D=3D 0B)
    goto <bb 7>; [30.00%]
  else
    goto <bb 6>; [70.00%]

  <bb 6> [local count: 375809640]:
  # .MEM_20 =3D VDEF <.MEM_2(D)>
  h =3D 0B;

  <bb 7> [local count: 536870912]:
  # .MEM_16 =3D PHI <.MEM_2(D)(5), .MEM_20(6)>
  # .MEM_21 =3D VDEF <.MEM_16>
  g =3D 0;
  # VUSE <.MEM_21>
  h.6_15 =3D h;
```=