[Bug c++/126215] ICE constant not recomputed when 'ADDR_EXPR' changed

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126215

--- Comment #5 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <[email protected]>:

https://gcc.gnu.org/g:706c0877e818b1035b763863b227d4d928ade421

commit r17-2663-g706c0877e818b1035b763863b227d4d928ade421
Author: Marek Polacek <[email protected]>
Date:   Wed Jul 22 17:28:03 2026 -0400

    c++: constant not recomputed when ADDR_EXPR changed [PR126215]

    Like in PR110822, the attached test produces an ICE in verify_address:

          error: constant not recomputed when 'ADDR_EXPR' changed

    since r10-7718, but it wasn't fixed by r15-7762.  The reason is that
    here we have:

      {.D.3013={.D.3006={.a={.ptr=&<retval>.D.3013.D.3006.a}},
                .D.3007={.b={.ptr=&<retval>.D.3013.D.3007.b}}}}

    and we replace '<retval>' with 'names', but we only call
    recompute_tree_invariant_expr for the first ADDR_EXPR, not the latter.
    For the second ADDR_EXPR d->changed will be false: the first replacement
    changed the shared tree <retval>.D.3013.  In replace_placeholders_r we
    unshare_expr when replacing a PLACEHOLDER_EXPR, but we also replace
    PLACEHOLDER_EXPRs in lookup_placeholder which didn't have this
    unsharing.

            PR c++/126215

    gcc/cp/ChangeLog:

            * constexpr.cc (lookup_placeholder): Do unshare_expr.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1z/constexpr-nsdmi1.C: New test.

    Reviewed-by: Jason Merrill <[email protected]>