Re: [debug-early] equate new DIE with DW_AT_specificationto a previous declaration

[Aldy Hernandez <aldyh at redhat dot com>]

On 03/17/2015 07:12 PM, Jason Merrill wrote:
> On 03/17/2015 03:58 PM, Aldy Hernandez wrote:
> > The problem is that, for -fno-implicit-templates, the decl is now
> > DECL_EXTERNAL, which means we never equate this new "DIE with
> > DW_AT_specification" to the DECL.  That is, we never fall through here:
> >
> >    else if (!DECL_EXTERNAL (decl))
> >      {
> >        HOST_WIDE_INT cfa_fb_offset;
> >
> >        struct function *fun = DECL_STRUCT_FUNCTION (decl);
> >
> >        if (!old_die || !get_AT (old_die, DW_AT_inline))
> >      equate_decl_number_to_die (decl, subr_die);
> >
> > However, when we call gen_subprogram_die() the third time through the
> > outlining_inline_function hook (late debug), we again try to add a
> > DW_AT_specification to the DIE cached from the first time around, but
> > this time we ICE because we're not supposed to have multiple
> > DW_AT_specification's pointing to the same DIE (the old original DIE).
>
> Why are we outlining a DECL_EXTERNAL function?

SRA is analyzing Object<int>::Method() and noticing that `this' is never 
used, so it's trying to rewrite the call to avoid passing `this' (by 
creating a clone).

SRA has no restrictions on whether a function is DECL_EXTERNAL.  For 
that matter, the SRA pass is called on all functions that have a gimple 
body, irregardless of DECL_EXTERNAL, courtesy of the pass manager:

          if (node->has_gimple_body_p ())
            callback (DECL_STRUCT_FUNCTION (node->decl), data);

...and since Object<int>::Method() has a gimple body even though it is 
marked DECL_EXTERNAL...we get the call into dwarf2out_abstract_decl.

> Incidentally,
>
> >           /* If we have no location information, this must be a
> >              partially generated DIE from early dwarf generation.
> >              Fall through and generate it.  */
>
> Why aren't we checking dumped_early here?

Good point.  I'll add an assert.

Aldy