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From: "ktkachov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/97442] New: Wrong represenation of AArch64 saba in RTL
Date: Thu, 15 Oct 2020 11:18:34 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97442

            Bug ID: 97442
           Summary: Wrong represenation of AArch64 saba in RTL
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ktkachov at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64

This is similar to the issue fixed in
https://gcc.gnu.org/git/?p=3Dgcc.git&a=3Dcommit;h=3D8544ed6eea68a80999504c8=
a4b21b77d29cd86e2

The representation of the SABA (and UABA) in RTL is not correct and the bel=
ow
testcase will abort at -O3 -fwrapv:

#define N 16
signed char a[] =3D {-100, -100, -100, -100,-100, -100, -100, -100, -100, -=
100,
-100, -100, -100, -100, -100, -100 };
signed char b[] =3D { 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, 100=
, 100,
100, 100, 100, 100 };

signed char out[N] =3D { 100, 100, 100, 100, 100, 100, 100, 100, 100, 100, =
100,
100, 100, 100, 100, 100 };

__attribute__ ((noinline,noipa))
void
foo (void)
{
  for (int i =3D 0; i < N; i++)
    {
      signed char diff =3D b[i] - a[i];
      out[i] +=3D diff > 0 ? diff : -diff;
    }
}

signed char out2[N] =3D { 100, 100, 100, 100, 100, 100, 100, 100, 100, 100,=
 100,
100, 100, 100, 100, 100 };

__attribute__ ((noinline,noipa))
void
foo_scalar (void)
{
  for (int i =3D 0; i < N; i++)
    {
      asm volatile ("");
      signed char diff =3D b[i] - a[i];
      out2[i] +=3D diff > 0 ? diff : -diff;
    }
}

int
main (void)
{
  foo ();
  foo_scalar ();
  for (int i =3D 0; i < N; i++)
    if (out[i] !=3D out2[i])
      __builtin_abort ();

  return 0;
}

due to function foo generating a saba when it shouldn't=