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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/112733] [14 Regression] ICE: Segmentation fault in
 wide-int.cc during GIMPLE pass: sccp
Date: Tue, 28 Nov 2023 17:43:00 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112733

--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 56707
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D56707&action=3Dedit
gcc14-pr112733-2.patch

Second patch to be tested.  Turned out it is more complicated than that.
If n > m, i.e. when divisor in absolute value is larger than dividend, we w=
ant
divmod_internal_2 to know that, such that e.g. it skips the main loop and l=
ooks
at correct most significant half limb of the divisor, but the
  if (s)
    for (i =3D 0; i < n; i++)
      b_remainder[i] =3D (b_dividend[i] >> s)
        | (b_dividend[i+1] << (HOST_BITS_PER_HALF_WIDE_INT - s));
  else
    for (i =3D 0; i < n; i++)
      b_remainder[i] =3D b_dividend[i];
loops in such case already may invoke UB, because they copy stuff from
b_dividend which just isn't there, at best some random upper bits, at worst
crash.  We can't copy more than there is in the array and need to tell the
caller how much we've initialized, so that wi_pack can take it into account.

While looking into this, I've noticed that I've allocated in case of XALLOC=
AVEC
multiplication and division/remainder calculations twice or 4 times as much
as really needed, so this patch fixes that too.=