[PATCH] Emit DWARF5 DW_AT_reference and DW_AT_rvalue_reference

Jason Merrill jason@redhat.com
Mon Oct 31 13:56:00 GMT 2016

On 10/24/2016 03:09 PM, Jakub Jelinek wrote:
> On Mon, Oct 24, 2016 at 02:34:04PM -0400, Jason Merrill wrote:
>> On Mon, Oct 24, 2016 at 10:29 AM, Jakub Jelinek <jakub@redhat.com> wrote:
>>> This is another addition in DWARF5.  The patch emits these attributes
>>> only for DW_TAG_subprogram for non-static ref-qualified member functions.
>>> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>> OK.
> Thanks, committed.
>>> We really should emit it also for DW_TAG_subroutine_type for PMF types,
>>> the problem is that for FUNCTION_TYPE/METHOD_TYPE, dwarf2out.c uses
>>> type_main_variant and get_qualified_type, neither of them understand
>>> ref-qualifies.  I think we'd need to change get_qualified_type to use
>>> some lang-hook which for C++ would also check the ref qualifiers, and then
>>> for these two avoid type_main_variant and instead use get_qualified_type
>>> to get the non-const/volatile/restrict etc. qualified one (and only then
>>> we can use the decl_dwarf_attribute langhook to ask the FE whether the
>>> attribute should be emitted).  Does that make sense, or do you have another
>>> approach?
>> Can we pull out the ref-qualifier before we clobber the qualifiers on the type?
> We could handle it like "reverse" flag, basically replace bool reverse with
> int that would hold bitmask of the flags, but I really don't understand how
> the reverse flag works right now, I don't see how it can work reliably when
> we use and rely on equate_type_number_to_die/lookup_type_die mechanism where
> we store just a single DIE for each type.  We either equate it to a type
> with DW_AT_endianity present, or not, and then the rest of the lookups will
> be just random.  I'm afraid to make it work reliably we'd need to somehow
> store both the "reverse" and "!reverse" DIEs for each type DIE, and
> similarly for the & and && flags.
> Or by changing get_qualified_die (in particular check_base_type) to use a
> langhook, we could at least for DW_AT_{reference,rvalue_reference} just use
> equate_type_number_to_die/lookup_type_die reliably (DW_AT_endianity issue
> remains).

Yeah, I think that adding a langhook is the right way to go.  The 
generic code clobbering C++ qualifiers is a frequent headache.


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