[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

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

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

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Are we sure we want to accept this?  I know we did, but that seems like an
accident (cp_fold_convert wasn't checking same_type_p).

Essentially it comes down to the fact that 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 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.  We could just add a
TYPE_PTRMEM_P check and go back to the GCC 7 error.