[Bug c/101537] -Wconversion false positive in ternary and |=

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101537

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:4e8c32ecfb87e723229dc6c08df8ea602e947f1e

commit r10-10666-g4e8c32ecfb87e723229dc6c08df8ea602e947f1e
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Jan 11 19:11:51 2022 +0100

    c-family: Fix up -W*conversion on bitwise &/|/^ [PR101537]

    The following testcases emit a bogus -Wconversion warning.  This is because
    conversion_warning function doesn't handle BIT_*_EXPR (only
unsafe_conversion_p
    that is called during the default: case, and that one doesn't handle
    SAVE_EXPRs added because the unsigned char & or | operands promoted to int
    have side-effects and =| or =& is used.

    The patch handles BIT_IOR_EXPR/BIT_XOR_EXPR like the last 2 operands of
    COND_EXPR by recursing on the two operands, if either of them doesn't fit
    into the narrower type, complain.  BIT_AND_EXPR too, but first it needs to
    handle some special cases that unsafe_conversion_p does, namely when one
    of the two operands is a constant.

    This fixes completely the pr101537.c test and for C also pr103881.c
    and doesn't regress anything in the testsuite, for C++ pr103881.c still
    emits the bogus warnings.
    This is because while the C FE emits in that case a SAVE_EXPR that
    conversion_warning can handle already, C++ FE emits
    TARGET_EXPR <D.whatever, ...>, something | D.whatever
    etc. and conversion_warning handles COMPOUND_EXPR by "recursing" on the
    rhs.  To handle that case, we'd need for TARGET_EXPR on the lhs remember
    in some hash map the mapping from D.whatever to the TARGET_EXPR and when
    we see D.whatever, use corresponding TARGET_EXPR initializer instead.

    2022-01-11  Jakub Jelinek  <jakub@redhat.com>

            PR c/101537
            PR c/103881
    gcc/c-family/
            * c-warn.c (conversion_warning): Handle BIT_AND_EXPR, BIT_IOR_EXPR
            and BIT_XOR_EXPR.
    gcc/testsuite/
            * c-c++-common/pr101537.c: New test.
            * c-c++-common/pr103881.c: New test.

    (cherry picked from commit 20e4a5e573e76f4379b353cc736215a5f10cdb84)