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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/113372] wrong code with _BitInt() arithmetics
 at -O1
Date: Mon, 15 Jan 2024 10:28:57 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113372

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Seems this is invalid variable sharing during RTL, I'm afraid we have tons =
of
open bugs against that, and I'm afraid I don't know anything what to do on =
the
bitint lowering side.
Bitint lowering creates 3 large variables:
  unsigned long bitint.8[75];
  unsigned long bitint.7[75];
  unsigned long bitint.6[100];
where bitint.6 corresponds to
  _3 =3D _2 % y_14(D);
and later when _3 isn't needed anymore to
  _8 =3D -y_14(D);
bitint.7 corresponds to
  _4 =3D -_3;
  _5 =3D (unsigned _BitInt(4745)) _4;
and bitint.8 corresponds to
  _7 =3D _5 * _6;
Reusing the same variable bitint.6 for 2 different _BitInt(6384) SSA_NAMEs
ought to be fine, they aren't live at the same time.
After lowering, we end up with:
  .DIVMODBITINT (0B, 0, &bitint.6, 6384, &D.2796, -8, &y, -6384);
  // Above fills in bitint.6 array
...
  loop which uses bitint.6 to compute bitint.7
  bitint.6 =3D{v} {CLOBBER(eos)};
...
  .MULBITINT (&bitint.8, 4745, &bitint.7, 4745, &D.2795, -8);
  // Above fills in bitint.8 array
...
  loop to compute bitint.6
...
  loop which uses bitint.6
...
  _21 =3D MEM[(unsigned long *)&bitint.8];
  _22 =3D (_BitInt(8)) _21;
  _18 =3D _22;
  return _18;
  // I.e. use bitint.8 for the return value

But unfortunately RTL expansion decides to use the same underlying memory f=
or
bitint.6 and bitint.8 arrays, even when the second uses of bitint.6 happens
when bitint.8 is live.

Or am I using incorrect CLOBBER kind when an underlying variable is used for
more than one SSA_NAME?  Like should that be just eob rather than eos?=