Hello,

With the recent work for PR debug/65549, we observed a regression in the 
generated debugging information. Take the attached reproducer, build it 
and look at the output DWARF:

      $ gcc -c -O1 -g foo.c
      $ objdump --dwarf=info foo.o
      [...]
       <2><4e>: Abbrev Number: 3 (DW_TAG_GNU_call_site)
          <4f>   DW_AT_low_pc      : 0x9
       <2><57>: Abbrev Number: 0

There is no DW_AT_abstract_origin attribute anymore, whereas there used 
to be one.

On PowerPC with -mlongcall, for instance, call instructions are indirect 
and we (at AdaCore) rely on this attribute to determine what function is 
actually called (it's easier this way than interpreting machine 
code...). The DWARF proposal for call sites also say debuggers should be 
able to use this attribute (to build virtual call stacks in the presence 
of tail calls), but I could not observe this in practice with GDB.

The attached patch is an attempt to restore this attribute. The logic 
behind it is: this is what we used to do previously for contexts that 
are alien translation unit (through the call to force_decl_die), so this 
should not harm.

Bootstrapped and regtested on x86_64-linux. Ok to commit?
Thank you in advance!

gcc/ChangeLog
         * dwarf2out.c (lookup_context_die): Return the DIE for the
         current compilation unit when the input context is a
         TRANSLATION_UNIT_DECL.

-- 
Pierre-Marie de Rodat