Question about extra debug (DWARF) info generated by gcc6/7

[Peter Edwards]

I've submitted bug 81135 to track this -
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81135

On Tue, Jun 20, 2017 at 8:27 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Mon, Jun 19, 2017 at 7:18 PM, Jason Merrill <jason@redhat.com> wrote:
>> On Mon, Jun 19, 2017 at 3:45 AM, Richard Biener
>> <richard.guenther@gmail.com> wrote:
>>> On Sat, Jun 17, 2017 at 9:09 AM, Siva Narayanan <sinaraya@arista.com> wrote:
>>>> Hello all,
>>>>
>>>> My colleague Peter managed to use "git bisect" on the git mirror of
>>>> gcc source code. The commit from a branch called "debug-early" seems
>>>> like a possible point when the new behavior got introduced.
>>>>
>>>> We have also looked at this conversation:
>>>> https://gcc.gnu.org/ml/gcc/2015-05/msg00046.html
>>>>
>>>> We would like to know if this work:
>>>>
>>>>>Shortly after the merge I'll work on a pass to prune unused decl DIEs as >we're presently creating more DIEs than mainline. This was expected, >and if I understood Jason correctly, it is ok to work on this post-merge. >However, even without such a pass, the .debug_info size difference is >reasonable:
>>>>
>>>> happened along with a future commit or if there is still some work
>>>> pending. As I wrote, in our environment the debug_info size difference
>>>> (from earlier 5.4 version of gcc) is significant that the object file
>>>> size change is non-trivial with gcc 6.3.1.
>>>
>>> To my knowledge this hasn't happened yet.
>>
>> Is there an open PR for this?
>
> I can't find one but IIRC there was one maybe only slightly related to
> this and thus already "fixed".  In talking to
> Pierre-Marie about some dwarf2 patch he has to not bail out early when
> trying to emit early debug for
> declarations (w/o struct function) I also mentioned the possibility of
> always generating those DIEs but later
> doing sth like the unused type DIE removal for (global) decl DIEs as
> well (just do a symtab lookup at early finish
> time and see if there are any references to it, if not, prune the DIE).
>
> Deciding on if sth is used at the point we call
> dwarf2out_early_global_decl seems premature given that
> is called by rest_of_decl_compilation which the FEs call happily
> during parsing already.
>
> Richard.
>
>> Jason