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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/111779] Fail to vectorize the struct include
 struct
Date: Thu, 12 Oct 2023 08:45:51 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111779

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c                           |tree-optimization
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
                 CC|                            |jamborm at gcc dot gnu.org
   Last reconfirmed|                            |2023-10-12

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
The issue is the aggregate copy:

t.c:26:22: missed:  not vectorized: more than one data ref in stmt: a =3D *=
_3;

which SRA fails to scalarize:

  <bb 3> [local count: 955630224]:
  # s_23 =3D PHI <s_18(3), 0(2)>
  # i_25 =3D PHI <i_20(3), 0(2)>
  _1 =3D (long unsigned int) i_25;
  _2 =3D _1 * 24;
  _3 =3D x_16(D) + _2;
  a =3D *_3;
  _4 =3D BIT_FIELD_REF <a.b4, 8, 64>;
  _12 =3D _4 & 1;
  _6 =3D (int) _12;
  s_18 =3D _6 + s_23;
  a =3D{v} {CLOBBER(eol)};
  i_20 =3D i_25 + 1;
  if (y_14(D) > i_20)

Candidate (2778): a
...
! Disqualifying a - No scalar replacements to be created.

the BIT_FIELD_REF is already created by early folding in
optimize_bit_field_compare folding (int) a.b4.f !=3D 0

    s =3D ((int) NON_LVALUE_EXPR <BIT_FIELD_REF <a.b4, 8, 64>> & 1) + s;

SRA could handle BIT_FIELD_REFs just fine - esp. quantities with
a byte size.  And then this folding is just premature...

Removing the folding that handles BF !=3D CST fixes it.  I know removing
all of it, esp. BF !=3D BF will regress some stuff.  I'll put this half-way
patch through testing.

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 82299bb7f1d..3db383360d6 100644
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -4695,7 +4695,7 @@ optimize_bit_field_compare (location_t loc, enum
tree_code code,
     return 0;

   if (const_p)
-    rreversep =3D lreversep;
+    return 0;
   else
    {
      /* If this is not a constant, we can only do something if bit positio=
ns,=