[Bug c++/95508] [10 Regression] ICE on unexpected expression implicit_conv_expr since r10-7096

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95508

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Marek Polacek
<mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:1bab254fd30c2b94a675b9057349fc80946375b1

commit r10-8315-g1bab254fd30c2b94a675b9057349fc80946375b1
Author: Marek Polacek <polacek@redhat.com>
Date:   Wed Jun 17 14:38:05 2020 -0400

    c++: ICE with IMPLICIT_CONV_EXPR in array subscript [PR95508]

    Since r10-7096 convert_like, when called in a template, creates an
    IMPLICIT_CONV_EXPR when we're converting to/from array type.

    In this test, we have e[f], and we're converting f (of type class A) to
    int, so convert_like in build_new_op_1 created the IMPLICIT_CONV_EXPR
    that got into cp_build_array_ref which calls maybe_constant_value.  My
    patch above failed to adjust this spot to call fold_non_dependent_expr
    instead, which can handle codes like I_C_E in a template.  Fixed by
    using a new function maybe_fold_non_dependent_expr, which, if the expr
    can't be evaluated to a constant, returns the original expression.

    gcc/cp/ChangeLog:

            PR c++/95508
            * constexpr.c (maybe_fold_non_dependent_expr): New.
            * cp-tree.h (maybe_fold_non_dependent_expr): Declare.
            * typeck.c (cp_build_array_ref): Call maybe_fold_non_dependent_expr
            instead of maybe_constant_value.

    gcc/testsuite/ChangeLog:

            PR c++/95508
            * g++.dg/template/conv16.C: New test.