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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.
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