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From: "linkw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/106322] [12/13 Regression] tree-vectorize:
 Wrong code at O2 level (-fno-tree-vectorize is working) since
 r12-2404-ga1d27560770818c5
Date: Wed, 10 Aug 2022 05:25:29 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106322

--- Comment #37 from Kewen Lin <linkw at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #36)
> You might need to do -O2 -fPIE -pie to reproduce the issue as debian is
> configured with --enable-default-pie

Thanks for the hint! I can reproduce this but it needs one more explicit cpu
type like -mcpu=3Dpower4/5/6. The problem comes from slp1, so
-fno-tree-slp-vectorize can make it pass.

It seems to expose one latent issue, for the code in vect_recog_mulhs_patte=
rn:

  vect_pattern_detected ("vect_recog_mulhs_pattern", last_stmt);

  /* Check for target support.  */
  tree new_vectype =3D get_vectype_for_scalar_type (vinfo, new_type);
  if (!new_vectype
      || !direct_internal_fn_supported_p
            (ifn, new_vectype, OPTIMIZE_FOR_SPEED))
    return NULL;

At this time, the new_vectype is=20

(gdb) pge new_vectype
vector(2) short unsigned int

the current target doesn't support umul_highpart optab for V2HImode at all,=
 but
the check doesn't fail since in the function direct_optab_supported_p

static bool
direct_optab_supported_p (direct_optab optab, tree_pair types,
                          optimization_type opt_type)
{
  machine_mode mode =3D TYPE_MODE (types.first);
  gcc_checking_assert (mode =3D=3D TYPE_MODE (types.second));
  return direct_optab_handler (optab, mode, opt_type) !=3D CODE_FOR_nothing;
}

(gdb) pge types.first
vector(2) short unsigned int
(gdb) p mode
$12 =3D E_SImode

the current target does support umul_highpart optab for SImode, so it doesn=
't
fail. But we expected to query with vector mode for the given type, it's wr=
ong
in functionality to use scalar insn for vector operation here, so this resu=
lt
is unexpected.=