[Bug c++/107295] [13 Regression] Rejected code in libreoffice with -m32 since r13-3290-g98e341130f87984a

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107295

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:2cc41601d9a948e8d612a21c3b9a44ce0b977747

commit r13-3438-g2cc41601d9a948e8d612a21c3b9a44ce0b977747
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Oct 21 18:04:54 2022 +0200

    c++: Don't shortcut TREE_CONSTANT vector type CONSTRUCTORs in
cxx_eval_constant_expression [PR107295]

    The excess precision support broke building skia (dependency of firefox)
    on ia32 (it has something like the a constexpr variable), but as the other
    cases show, it is actually a preexisting problem if one uses casts from
    constants with wider floating point types.
    The problem is that cxx_eval_constant_expression tries to short-cut
    processing of TREE_CONSTANT CONSTRUCTORs if they satisfy
    reduced_constant_expression_p - instead of calling cxx_eval_bare_aggregate
    on them it just verifies flags and if they are TREE_CONSTANT even after
    that, just fold.
    Now, on the testcase we have a TREE_CONSTANT CONSTRUCTOR containing
    TREE_CONSTANT NOP_EXPR of REAL_CST.  And, fold, which isn't recursive,
    doesn't optimize that into VECTOR_CST, while later on we are only able
    to optimize VECTOR_CST arithmetics, not arithmetics with vector
    CONSTRUCTORs.
    The following patch fixes that by rejecting CONSTRUCTORs with vector type
    in reduced_constant_expression_p regardless of whether they have
    CONSTRUCTOR_NO_CLEARING set or not, folding result in
cxx_eval_bare_aggregate
    even if nothing has changed but it wasn't non-constant and removing folding
    from the TREE_CONSTANT reduced_constant_expression_p short-cut.

    2022-10-21  Jakub Jelinek  <jakub@redhat.com>

            PR c++/107295
            * constexpr.cc (reduced_constant_expression_p) <case CONSTRUCTOR>:
            Return false for VECTOR_TYPE CONSTRUCTORs even without
            CONSTRUCTOR_NO_CLEARING set on them.
            (cxx_eval_bare_aggregate): If constant but !changed, fold before
            returning VECTOR_TYPE_P CONSTRUCTOR.
            (cxx_eval_constant_expression) <case CONSTRUCTOR>: Don't fold
            TREE_CONSTANT CONSTRUCTOR, just return it.

            * g++.dg/ext/vector42.C: New test.