Re: [PATCH 1/2] DWARF: process all TYPE_DECL nodes when iterating on scopes

[Pierre-Marie de Rodat <derodat at adacore dot com>]

On 01/18/2016 12:18 PM, Richard Biener wrote:
> Looking for TYPE_DECL_IS_STUB uses I come along dwarf2out_ignore_block
> which you'd need to change as well I think.

That is true, thank you!

First, Iâll answer your last point:
> Btw, not sure how you get at the "wrong" debug info gen order, I
> can't seem to get at it with a C testcase.
>
> As with the other patch this misses a testcase.

Thatâs true, sorry for that. I could not yield a C reproducer neither, 
so hereâs my original Ada testcase: I will include it in the next patch 
under gnat.dg.

So the problem Iâm trying to address is the following: Record_Type is 
declared in Debug5, and it is referenced by the R parameter in 
Debug5.Process (so far, so good). Now, because debug info for 
Debug5.Process is emitted before the one for Debug5, Record_Type is 
emitted in the global scope and is not relocated under Debug5 afterwards.

> > -  else if (TREE_CODE (decl_or_origin) == TYPE_DECL
> > -           && TYPE_DECL_IS_STUB (decl_or_origin))
> > +  else if (TREE_CODE (decl_or_origin) == TYPE_DECL)
> >       die = lookup_type_die (TREE_TYPE (decl_or_origin));
>
> But ... I think this change is wrong.  It is supposed to use the _type_ DIE
> in case the FE didn't create a proper TYPE_DECL.  So I think what is
> maybe missing is
>
>    else if (TREE_CODE (decl_or_origin) == TYPE_DECL)
>      die = lookup_decl_die (decl_or_origin);
>
> ?  That is, why should we lookup the type if the type-decl isn't a stub?

While I agree that for non-stub TYPE_DECL, it is sound to look for the 
decl itself rather than the type, this does not fix the bug I intended 
to fix. Indeed, when we reach this point for the TYPE_DECL corresponding 
to Record_Type, add_type_attribute just creates a DW_TAG_typedef for it, 
and the call it does to modified_type just returns the existing 
DW_TAG_record_type (still in the global scope).

So assuming your proposal of the change is correct, should we then use 
TYPE_CONTEXT in order to (potentially) relocate TREE_TYPE (decl) in 
add_type_attribute?

--
Pierre-Marie de Rodat

--  The aim of this test is to check that Ada types appear in the proper
--  context in the debug info.
-- 
--  Checking this directly would be really tedious just scanning for assembly
--  lines, so instead we rely on DWARFv4's .debug_types sections, which must be
--  created only for global-scope types. Checking the number of .debug_types is
--  some hackish way to check that types are output in the proper context (i.e.
--  at global or local scope).
--
--  { dg-options "-g -gdwarf-4 -cargs -fdebug-types-section -dA" }
--  { dg-final { scan-assembler-times "\\(DIE \\(0x\[a-f0-9\]*\\) DW_TAG_type_unit\\)" 0 } }

procedure Debug5 is
   type Array_Type is array (Natural range <>) of Integer;
   type Record_Type (L1, L2 : Natural) is record
      I1 : Integer;
      A1 : Array_Type (1 .. L1);
      I2 : Integer;
      A2 : Array_Type (1 .. L2);
      I3 : Integer;
   end record;

   function Get (L1, L2 : Natural) return Record_Type is
      Result : Record_Type (L1, L2);
   begin
      Result.I1 := 1;
      for I in Result.A1'Range loop
         Result.A1 (I) := I;
      end loop;
      Result.I2 := 2;
      for I in Result.A2'Range loop
         Result.A2 (I) := I;
      end loop;
      Result.I3 := 3;
      return Result;
   end Get;

   R1 : Record_Type := Get (0, 0);
   R2 : Record_Type := Get (1, 0);
   R3 : Record_Type := Get (0, 1);
   R4 : Record_Type := Get (2, 2);

   procedure Process (R : Record_Type) is
   begin
      null;
   end Process;

begin
   Process (R1);
   Process (R2);
   Process (R3);
   Process (R4);
end Debug5;