Hi Jakub,
On Mon, Aug 24, 2020 at 07:40:51PM +0200, Jakub Jelinek wrote:
> On Mon, Aug 24, 2020 at 02:56:55PM +0200, Mark Wielaard wrote:
> > In DWARF5 class variables (static data members) are represented with a
> > DW_TAG_variable instead of a DW_TAG_member. Make sure the variable isn't
> > optimized away in the constexpr-var-1.C testcase so we can still match (2)
> > const_expr in the the assembly output.
> >
> > Note that the same issue causes some failures in the gdb testsuite
> > for static data members when we enable DWARF5 by default:
> > https://sourceware.org/bugzilla/show_bug.cgi?id=26525
> > ---
> > gcc/testsuite/g++.dg/debug/dwarf2/constexpr-var-1.C | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/gcc/testsuite/g++.dg/debug/dwarf2/constexpr-var-1.C
> > b/gcc/testsuite/g++.dg/debug/dwarf2/constexpr-var-1.C
> > index 19062e29fd59..c6ad3f645379 100644
> > --- a/gcc/testsuite/g++.dg/debug/dwarf2/constexpr-var-1.C
> > +++ b/gcc/testsuite/g++.dg/debug/dwarf2/constexpr-var-1.C
> > @@ -7,3 +7,4 @@ struct S
> > {
> > static constexpr int b = 6;
> > } s;
> > +const int &c = s.b;
>
> This looks incorrect to me, that is a workaround for a real GCC bug.
I was discussing this after the BoF with Tom Tromey (CCed) and he also
thought gdb could/should actually support the DWARF5 representation,
but because the DW_TAG_variable was removed because the static data
member wasn't referenced in the gdb testcases.
> Shouldn't we instead do something like (untested) following patch?
> I mean, for DWARF < 5 the static data members were using DW_TAG_member,
> which has been always marked by the function, so IMHO we should also always
> mark the DW_TAG_variables at the class scope that replaced those.
>
> 2020-08-24 Jakub Jelinek <ja...@redhat.com>
>
> * dwarf2out.c (prune_unused_types_walk): Mark DW_TAG_variable DIEs
> at class scope for DWARF5+.
This looks really good, and it makes all the FAILs in the gdb bug
report PASS (when build with -gdwarf-5 as default).
> --- gcc/dwarf2out.c.jj 2020-07-28 15:39:09.883757946 +0200
> +++ gcc/dwarf2out.c 2020-08-24 19:33:16.503961786 +0200
> @@ -29392,6 +29392,13 @@ prune_unused_types_walk (dw_die_ref die)
> if (die->die_perennial_p)
> break;
>
> + /* For static data members, the declaration in the class is supposed
> + to have DW_TAG_member tag in DWARF{3,4} but DW_TAG_variable in
> + DWARF5. DW_TAG_member will be marked, so mark even such
> + DW_TAG_variables in DWARF5. */
> + if (dwarf_version >= 5 && class_scope_p (die->die_parent))
> + break;
> +
> /* premark_used_variables marks external variables --- don't mark
> them here. But function-local externals are always considered
> used. */
Thanks,
Mark
