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From: "liuhongt at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/115406] [15 Regression] wrong code with vector compare
 at -O0 with -mavx512f since r15-920-gb6c6d5abf0d31c
Date: Tue, 11 Jun 2024 02:55:15 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115406

--- Comment #3 from Hongtao Liu <liuhongt at gcc dot gnu.org> ---
typedef __attribute__((__vector_size__ (1))) char V;

char
foo (V v)
{
  return ((V) v =3D=3D v)[0];
}

int
main ()
{
  char x =3D foo ((V) { });
  if (x !=3D -1)
    __builtin_abort ();
}

w/ vcond_mask_qiqi, it's not lowered by veclower, and we get

char foo (V v)
{
  vector(1) signed char D.5142;
  char D.5141;
  vector(1) <signed-boolean:8> _1;
  vector(1) signed char _2;
  char _5;

  <bb 2> :
  _1 =3D { -1 };
  _2 =3D VEC_COND_EXPR <_1, { -1 }, { 0 }>;
  D.5142 =3D _2;
  _5 =3D VIEW_CONVERT_EXPR<char>(D.5142);

  <bb 3> :
<L0>:
  return _5;
}

But it's further simplified to=20

char foo (V v)
{
  vector(1) signed char D.3765;
  char D.3764;
  vector(1) <signed-boolean:8> _1;
  vector(1) signed char _2;
  char _5;

  <bb 2> :
  _1 =3D { -1 };
  _2 =3D VIEW_CONVERT_EXPR<vector(1) signed char>(_1);
  D.3765 =3D _2;
  _5 =3D VIEW_CONVERT_EXPR<char>(D.3765);

  <bb 3> :
<L0>:
  return _5;

}

by isel

and for _2 =3D VIEW_CONVERT_EXPR<vector(1) signed char>(_1); we explicitly =
clear
the upper bits due to PR113576, and then we get 1 hit the abort.

It sound to me=20
  _1 =3D { -1 };
  _2 =3D VEC_COND_EXPR <_1, { -1 }, { 0 }>;
shouldn't be simplified to=20
_2 =3D VIEW_CONVERT_EXPR<vector(1) signed char>(_1);

when nunits is less than mode precision since the upper bit will be cleared=
.=