Re: [PATCH] Early LTO debug TODO

[Jason Merrill <jason at redhat dot com>]

On Thu, Aug 31, 2017 at 4:03 PM, Richard Biener <rguenther@suse.de> wrote:
> On Thu, 31 Aug 2017, Richard Biener wrote:
>
>>
>> As suspected during review the DECL_ABSTRACT_P handling in
>> gen_formal_parameter_die is no longer necessary so the following
>> patch removes it.
>>
>> [LTO] bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
>> The gdb testsuite shows no regression.
>>
>> Will apply after testing finished.
>
> Ok, so it doesn't work - it regresses for example
> gcc.dg/debug/dwarf2/inline1.c because we end up annotating the
> abstract DIE with a location.  This is because in gen_subprogram_die
> (with decl set as abstract-self and thus generating a concrete
> instance subroutine die) we call
>
>           else if (parm && !POINTER_BOUNDS_P (parm))
>             {
>               dw_die_ref parm_die = gen_decl_die (parm, NULL, NULL,
> subr_die);
>
> thus unconditionally pass NULL as origin where gen_formal_parameter_die
> just has
>
>   /* If we have a previously generated DIE, use it, unless this is an
>      concrete instance (origin != NULL), in which case we need a new
>      DIE with a corresponding DW_AT_abstract_origin.  */
>   bool reusing_die;
>   if (parm_die && origin == NULL)
>     reusing_die = true;
>   else
>     {
>       parm_die = new_die (DW_TAG_formal_parameter, context_die, node);
>       reusing_die = false;
>     }
>
> but obviously that logic is flawed with us passing origin as NULL...
>
> What saved us here is the check whether the existing param_die has
> the correct parent, if not we didn't re-use it.  OTOH for die_parent
> == NULL we have the extra check that would have been dead code.
>
> Any hint as to whether we should pass in anything as origin or
> whether we should keep the existing die_parent logic somehow?
> (do we ever get a NULL context_die passed?)

The problem is that we aren't checking decl_ultimate_origin soon
enough, and thereby setting origin.

Tested x86_64-pc-linux-gnu, applying to trunk:

Attachment: parm-debug.diff
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