[Bug debug/97599] [8/9/10/11 Regression] missing unspecified_parameters DIE in DWARF for functions with variable arguments

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97599

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think the main confusion is as to how we represent IPA clones in debug,
namely making them have an abstract origin to the cloned function even though
their signatures do not match.  In reality we're creating a new function
[entry] with a different signature.  I think a better representation for
a function clone would be

 <1><ab>: Abbrev Number: 10 (DW_TAG_subprogram)
          DW_AT_artificial : 1
<clone signature>

 <2>      DW_TAG_inlined_subroutine <original function DIE>

plus the parameter mapping.  Thus represent a clone as what it really is,
a new function calling the old one with appropriate parameters.

This doesn't work for the function splitting tail though (IIRC we had another
PR about that).

The question is whether we need to have any debug for the formal parameters
of clones or if it is enough to appropriately specify the
DW_TAG_inlined_subroutine (that's where users would expect breakpoints as
well).

So in the end I don't believe the current situation is "fixable" since we
cannot distinguish clones from abstract vs. concrete instances in the
DWARF itself.  And the abstract origin we have on the tree level is just
misleading.