[Bug c++/94050] [10 Regression] C++ ABI change on armv7hl-linux-gnueabi since r10-1302

[Bug c++/94050] [10 Regression] C++ ABI change on armv7hl-linux-gnueabi since r10-1302

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94050

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
commit r10-7089-g8475f2902a2e2ca5f7ace8bc5265bd1a815dda20
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Mar 5 14:07:25 2020 -0500

    c++: Fix ABI issue with alignas on armv7hl [PR94050]

    The static_assert in the following test was failing on armv7hl because
    we were disregarding the alignas specifier on Cell.  BaseShape's data
    takes up 20B on 32-bit architectures, but we failed to round up its
    TYPE_SIZE.  This happens since the
    <https://gcc.gnu.org/ml/gcc-patches/2019-06/msg01189.html>
    patch: here, in layout_class_type for TenuredCell, we see that the size
    of TenuredCell and its CLASSTYPE_AS_BASE match, so we set

      CLASSTYPE_AS_BASE (t) = t;

    While TYPE_USER_ALIGN of TenuredCell was 0, because finalize_type_size
    called from finish_record_layout reset it, TYPE_USER_ALIGN of its
    CLASSTYPE_AS_BASE still remained 1.  After we replace it, it's no longer
    1.  Then we perform layout_empty_base_or_field for TenuredCell and since
    TYPE_USER_ALIGN of its CLASSTYPE_AS_BASE is now 0, we don't do this
    adjustment:

      if (CLASSTYPE_USER_ALIGN (type))
        {
          rli->record_align = MAX (rli->record_align, CLASSTYPE_ALIGN (type));
          if (warn_packed)
            rli->unpacked_align = MAX (rli->unpacked_align, CLASSTYPE_ALIGN
(type));
          TYPE_USER_ALIGN (rli->t) = 1;
        }

    where rli->t is BaseShape.  Then finalize_record_size won't use the
    correct rli->record_align and therefore
      /* Round the size up to be a multiple of the required alignment.  */
      TYPE_SIZE (rli->t) = round_up (unpadded_size, TYPE_ALIGN (rli->t));
    after this we end up with the wrong size.

    Since the original fix was to avoid creating extra copies for LTO
    purposes, I think the following fix should be acceptable.

            PR c++/94050 - ABI issue with alignas on armv7hl.
            * class.c (layout_class_type): Don't replace a class's
            CLASSTYPE_AS_BASE if their TYPE_USER_ALIGN don't match.

            * g++.dg/abi/align3.C: New test.

[Bug c++/94050] [10 Regression] C++ ABI change on armv7hl-linux-gnueabi since r10-1302

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94050

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed.