[Bug c++/107574] [10/11/12/13 Regression] ICE: tree check in cp_fold_convert with ptr to member field cast inside a class not completed and inherent since r9-50-gd760b06868d660bc

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107574

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:de81e06273c613d7e06cbe2c8d9e72826c638056

commit r13-6400-gde81e06273c613d7e06cbe2c8d9e72826c638056
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Feb 2 18:15:37 2023 -0500

    c++: can't eval PTRMEM_CST in incomplete class [PR107574]

    Here we're attempting to evaluate a PTRMEM_CST in a class that hasn't
    been completed yet, but that doesn't work:

            /* We can't lower this until the class is complete.  */
            if (!COMPLETE_TYPE_P (DECL_CONTEXT (member)))
              return cst;

    and then this unlowered PTRMEM_CST is used as EXPR in

        tree op1 = build_nop (ptrdiff_type_node, expr);

    and we crash in a subsequent cp_fold_convert which gets
type=ptrdiff_type_node,
    expr=PTRMEM_CST and does

      else if (TREE_CODE (expr) == PTRMEM_CST
               && same_type_p (TYPE_PTRMEM_CLASS_TYPE (type),
                               PTRMEM_CST_CLASS (expr)))

    where TYPE_PTRMEM_CLASS_TYPE (type) is going to crash since the type
    is ptrdiff_type_node.  We could just add a TYPE_PTRMEM_P check before
    accessing TYPE_PTRMEM_CLASS_TYPE but I think it's nicer to explain why
    we couldn't evaluate the expression.

            PR c++/107574

    gcc/cp/ChangeLog:

            * constexpr.cc (cxx_eval_constant_expression): Emit an error when
            a PTRMEM_CST cannot be evaluated.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/ptrmem-cst1.C: New test.