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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/102124] [11/12 Regression] -ftree-loop-vectorize Causing
 Data To Lose Sign Bit on AARCH64 Platform
Date: Mon, 30 Aug 2021 08:32:46 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102124

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |joelh at gcc dot gnu.org,
                   |                            |rsandifo at gcc dot gnu.org
           Priority|P3                          |P2
   Target Milestone|---                         |11.3
            Summary|GCC 11.2.1                  |[11/12 Regression]
                   |-ftree-loop-vectorize       |-ftree-loop-vectorize
                   |Causing Data To Lose Sign   |Causing Data To Lose Sign
                   |Bit on AARCH64 Platform     |Bit on AARCH64 Platform
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2021-08-30

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r11-5160-g9fc9573f9a5e9432e53c7de93985cfbd267f0309 .

Slightly reduced testcase:
int
foo (const unsigned char *a, const unsigned char *b, unsigned long len)
{
  int ab, ba;=20
  unsigned long i;
  for (i =3D 0, ab =3D 0, ba =3D 0; i < len; i++)
    {
      ab |=3D a[i] - b[i];
      ba |=3D b[i] - a[i];
    }=20=20=20
  return (ab | ba) >=3D 0;
}

int main ()
{
  unsigned char a[32] =3D {'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a'=
, 'a',
'a', 'a', 'a', 'a', 'a'};
  unsigned char b[32] =3D {'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a'=
, 'a',
'a', 'a', 'a', 'a', 'a'};
  unsigned char c[32] =3D {'b', 'b', 'b', 'b', 'b', 'b', 'b', 'b', 'b', 'b'=
, 'b',
'b', 'b', 'b', 'b', 'b'};
  if (!foo (a, b, 16))
    __builtin_abort ();
  if (foo (a, c, 16))
    __builtin_abort ();
  return 0;
}=