[Bug middle-end/91226] wrong propagation of non-canonical _Decimal64 and _Decimal128 constant (BID only)

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91226

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-8 branch has been updated by Joseph Myers <jsm28@gcc.gnu.org>:

https://gcc.gnu.org/g:a8d3c5702a422025e42b22ce860e245b50ff57a2

commit r8-9931-ga8d3c5702a422025e42b22ce860e245b50ff57a2
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Mon Jan 13 22:15:01 2020 +0000

    Fix libdecnumber handling of non-canonical BID significands (PR
middle-end/91226).

    As reported in bug 91226, the libdecnumber code used on the host to
    interpret DFP values in the BID encoding fails, for _Decimal64 and
    _Decimal128, to check for the case where a significand is too large
    and so specified in IEEE 754 to be a non-canonical encoding of the
    zero significand.  This patch adds the required handling of that case,
    together with tests both using -O2 (testing this host code) and -O0
    (testing libgcc code, which already worked before the patch); the
    tests also cover _Decimal32, which already had the required check.

    In the _Decimal128 case, where the code previously completely ignored
    the case where the first four bits of the combination field are 1100,
    1101 or 1110, the logic for determining the correct quantum exponent
    in that case is also newly added by this patch, so tests are added for
    that as well (again, libgcc already handled it correctly when the
    conversion was done at runtime rather than at compile time).

    Bootstrapped with no regressions for x86_64-pc-linux-gnu.

        PR middle-end/91226
    libdecnumber:
        * bid/bid2dpd_dpd2bid.c (_bid_to_dpd64): Handle non-canonical
        significands.
        (_bid_to_dpd128): Likewise.  Check for case where combination
        field starts 1100, 1101 or 1110.

    gcc/testsuite:
        * gcc.dg/dfp/bid-non-canonical-d128-1.c,
        gcc.dg/dfp/bid-non-canonical-d128-2.c,
        gcc.dg/dfp/bid-non-canonical-d128-3.c,
        gcc.dg/dfp/bid-non-canonical-d128-4.c,
        gcc.dg/dfp/bid-non-canonical-d32-1.c,
        gcc.dg/dfp/bid-non-canonical-d32-2.c,
        gcc.dg/dfp/bid-non-canonical-d64-1.c,
        gcc.dg/dfp/bid-non-canonical-d64-2.c: New tests.

    (cherry picked from commit 0fad54f0a88160e81c3150b63c91fd9809665474)