https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101378
--- Comment #11 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:10db7573014008ff867098206f51012d501ab57b commit r12-5148-g10db7573014008ff867098206f51012d501ab57b Author: Jakub Jelinek <ja...@redhat.com> Date: Thu Nov 11 10:14:04 2021 +0100 dwarf2out: Fix up field_byte_offset [PR101378] For PCC_BITFIELD_TYPE_MATTERS field_byte_offset has quite large code to deal with it since many years ago (see it e.g. in GCC 3.2, although it used to be on HOST_WIDE_INTs, then on double_ints, now on offset_ints). But that code apparently isn't able to cope with members with empty class types with [[no_unique_address]] attribute, because the empty classes have non-zero type size but zero decl size and so one can end up from the computation with negative offset or offset 1 byte smaller than it should be. For !PCC_BITFIELD_TYPE_MATTERS, we just use tree_result = byte_position (decl); which seems exactly right even for the empty classes or anything which is not a bitfield (and for which we don't add DW_AT_bit_offset attribute). So, instead of trying to handle those no_unique_address members in the current already very complicated code, this limits it to bitfields. stor-layout.c PCC_BITFIELD_TYPE_MATTERS handling also affects only bitfields, twice it checks DECL_BIT_FIELD and once DECL_BIT_FIELD_TYPE. As discussed, this patch uses DECL_BIT_FIELD_TYPE check, because DECL_BIT_FIELD might be cleared for some bitfields with bitsizes multiple of BITS_PER_UNIT and e.g. struct S { int e; int a : 1, b : 7, c : 8, d : 16; } s; struct T { int a : 1, b : 7; long long c : 8; int d : 16; } t; int main () { s.c = 0x55; s.d = 0xaaaa; t.c = 0x55; t.d = 0xaaaa; s.e++; } has different debug info with DECL_BIT_FIELD check. 2021-11-11 Jakub Jelinek <ja...@redhat.com> PR debug/101378 * dwarf2out.c (field_byte_offset): Do the PCC_BITFIELD_TYPE_MATTERS handling only for DECL_BIT_FIELD_TYPE decls. * g++.dg/debug/dwarf2/pr101378.C: New test.
