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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/96931] [11 Regression] ICE in add_phi_arg, at
 tree-phinodes.c:359
Date: Fri, 04 Sep 2020 08:34:48 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96931

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
So the testcase only triggers on trunk because store commoning is new there=
 and
it transforms (interestingly!)

  <bb 2> [local count: 10631108]:
  p3 ();
  bl =3D 0;

  <bb 3> [local count: 1073741824]:
  bl.0_1 =3D bl;
  _2 =3D bl.0_1 + 1;
  bl =3D _2;
  goto <bb 3>; [100.00%]

to

  <bb 2> [local count: 10631108]:
  p3 ();

  <bb 3> [local count: 1073741824]:
  # _8 =3D PHI <0(2), _2(3)>
  bl =3D _8;
  bl.0_1 =3D bl;
  _2 =3D bl.0_1 + 1;
  goto <bb 3>; [100.00%]

which predcom tries to "improve" to

  <bb 2> [local count: 10631108]:
  p3 ();
  _10 =3D bl;

  <bb 3> [local count: 1073741824]:
  # _8 =3D PHI <0(2), _2(4)>
  # bl_lsm0.3_7 =3D PHI <_10(2), bl_lsm0.3_6(4)>
  bl =3D _8;
  bl_lsm0.3_6 =3D _8;
  bl.0_1 =3D bl_lsm0.3_6;
  _2 =3D bl.0_1 + 1;

  <bb 4> [local count: 1073741824]:
  goto <bb 3>; [100.00%]

so the situation is quite arcane and eventually not worth fixing on branche=
s.=