[Bug tree-optimization/98474] [8/9 Regression] incorrect results using __uint128_t

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98474

--- Comment #11 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-8 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:8cbe9fc12453026f7efc02dad569c6270d595427

commit r8-10872-g8cbe9fc12453026f7efc02dad569c6270d595427
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Dec 31 11:06:56 2020 +0100

    wide-int: Fix wi::to_mpz [PR98474]

    The following testcase is miscompiled, because niter analysis miscomputes
    the number of iterations to 0.
    The problem is that niter analysis uses mpz_t (wonder why, wouldn't
    widest_int do the same job?) and when wi::to_mpz is called e.g. on the
    TYPE_MAX_VALUE of __uint128_t, it initializes the mpz_t result with wrong
    value.
    wi::to_mpz has code to handle negative wide_ints in signed types by
    inverting all bits, importing to mpz and complementing it, which is fine,
    but doesn't handle correctly the case when the wide_int's len (times
    HOST_BITS_PER_WIDE_INT) is smaller than precision when wi::neg_p.
    E.g. the 0xffffffffffffffffffffffffffffffff TYPE_MAX_VALUE is represented
    in wide_int as 0xffffffffffffffff len 1, and wi::to_mpz would create
    0xffffffffffffffff mpz_t value from that.
    This patch handles it by adding the needed -1 host wide int words (and has
    also code to deal with precision that aren't multiple of
    HOST_BITS_PER_WIDE_INT).

    2020-12-31  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/98474
            * wide-int.cc (wi::to_mpz): If wide_int has MSB set, but type
            is unsigned and excess negative, append set bits after len until
            precision.

            * gcc.c-torture/execute/pr98474.c: New test.

    (cherry picked from commit a4d191d08c6acb24034af4182b3524e6ef97546c)