[Bug c++/117980] [15 Regression] ICE in in cxx_eval_outermost_constant_expr, at cp/constexpr.cc:8950 on nix-2.25.2 since r15-6052-g12de1942a0a673

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117980

--- Comment #11 from GCC 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:fa99002538bc91c869f3b1fd9af7f14e410e1e1a

commit r15-6369-gfa99002538bc91c869f3b1fd9af7f14e410e1e1a
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue Dec 10 18:43:56 2024 -0500

    c++: ICE in TARGET_EXPR evaluation in cp_fold_r [PR117980]

    This ICE started with the recent prvalue optimization (r15-6052).  In
    cp_fold_r we have:

          if (tree &init = TARGET_EXPR_INITIAL (stmt))
            {
              cp_walk_tree (&init, cp_fold_r, data, NULL);
              // ...
              tree folded = maybe_constant_init (init, TARGET_EXPR_SLOT
(stmt));

    What can happen here is that originally the TARGET_EXPR is:

        TARGET_EXPR <D.2747, <<< Unknown tree: aggr_init_expr
          5
          __ct_comp
          D.2747
          (struct subrange *) <<< Unknown tree: void_cst >>>
          &TARGET_EXPR <D.2707, {.it=TARGET_EXPR <D.2695, ...>}> >>>>

    but after the first cp_walk_tree we fold the D.2707 TARGET_EXPR into:

        TARGET_EXPR <D.2707, <<< Unknown tree: expr_stmt
          D.2707.it = TARGET_EXPR <D.2695, ...> >>>>

    and then we pass the EXPR_STMT to maybe_constant_init, with D.2707 as
    the object.  But their types don't match anymore, so we crash.  We'd
    have to pass D.2707.it as the object for it to work.

    This patch adjusts cxx_eval_outermost_constant_expr to take the object's
    type if available.

    constexpr-prvalue3.C is reduced from a large std::ranges libstdc++ test.

            PR c++/117980

    gcc/cp/ChangeLog:

            * constexpr.cc (cxx_eval_outermost_constant_expr): If there's
            an object to initialize, take its type.  Don't set the type
            in the constexpr dtor case.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/constexpr-prvalue2.C: New test.
            * g++.dg/cpp0x/constexpr-prvalue3.C: New test.

    Co-authored-by: Jason Merrill <jason@redhat.com>