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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/99648] [11 regression] gcc.dg/torture/pr71522.c fails
 starting with r11-165 for 32 bits
Date: Fri, 09 Apr 2021 16:48:19 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99648

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Ok, I can finally reproduce, one needs -m32 -Os -mcpu=3Dpower7 (or power8 or
power9) to reproduce.
And the bug is created in store_bit_field_1 doing:
      rtx sub;
      HOST_WIDE_INT regnum;
      poly_uint64 regsize =3D REGMODE_NATURAL_SIZE (GET_MODE (op0));
      if (known_eq (bitnum, 0U)
          && known_eq (bitsize, GET_MODE_BITSIZE (GET_MODE (op0))))
        {
          sub =3D simplify_gen_subreg (GET_MODE (op0), value, fieldmode, 0);
          if (sub)
            {
              if (reverse)
                sub =3D flip_storage_order (GET_MODE (op0), sub);
              emit_move_insn (op0, sub);
              return true;
            }
        }
(there is similar code later on).
value is
(const_vector:V16QI [
        (const_int 65 [0x41]) repeated x15
        (const_int 0 [0])
    ])
simplify_gen_subreg from V16QImode to TFmode makes
(const_double:TF 4.5232690196078126318752765655517578125e+6
[0x0.8a0a0a0a0a0904p+23])
out of that and the problem is that this constant doesn't convert back to v=
alue
when simplify_gen_subreg converted back to V16QImode, instead it yields
(const_vector:V16QI [
        (const_int 65 [0x41])
        (const_int 81 [0x51])
        (const_int 65 [0x41]) repeated x5
        (const_int 32 [0x20])
        (const_int 62 [0x3e])
        (const_int 0 [0]) repeated x7
    ])
So, to me this looks like a dup of PR95450, except in simplify-rtx.c rather
than in fold-const.c.
Do we want to do the same thing in simplify_subreg and try to convert back =
for
MODE_COMPOSITE_P?=