10db757301
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 <jakub@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.
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