Re: [PATCH] [DWARF] Fix hierarchy of debug information for offload kernels.

[Richard Biener <richard.guenther@gmail.com>]

On Fri, Jul 16, 2021 at 10:23 PM Hafiz Abid Qadeer
<abid_qadeer@mentor.com> wrote:
>
> On 15/07/2021 13:09, Richard Biener wrote:
> > On Thu, Jul 15, 2021 at 12:35 PM Hafiz Abid Qadeer
> > <abid_qadeer@mentor.com> wrote:
> >>
> >> On 15/07/2021 11:33, Thomas Schwinge wrote:
> >>>
> >>>> Note that the "parent" should be abstract but I don't think dwarf has a
> >>>> way to express a fully abstract parent of a concrete instance child - or
> >>>> at least how GCC expresses this causes consumers to "misinterpret"
> >>>> that.  I wonder if adding a DW_AT_declaration to the late DWARF
> >>>> emitted "parent" would fix things as well here?
> >>>
> >>> (I suppose not, Abid?)
> >>>
> >>
> >> Yes, adding DW_AT_declaration does not fix the problem.
> >
> > Does emitting
> >
> > DW_TAG_compile_unit
> >   DW_AT_name    ("<artificial>")
> >
> >   DW_TAG_subprogram // notional parent function (foo) with no code range
> >     DW_AT_declaration 1
> > a:    DW_TAG_subprogram // offload function foo._omp_fn.0
> >       DW_AT_declaration 1
> >
> >   DW_TAG_subprogram // offload function
> >   DW_AT_abstract_origin a
> > ...
> >
> > do the trick?  The following would do this, flattening function definitions
> > for the concrete copies:
> >
> > diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
> > index 82783c4968b..a9c8bc43e88 100644
> > --- a/gcc/dwarf2out.c
> > +++ b/gcc/dwarf2out.c
> > @@ -6076,6 +6076,11 @@ maybe_create_die_with_external_ref (tree decl)
> >    /* Peel types in the context stack.  */
> >    while (ctx && TYPE_P (ctx))
> >      ctx = TYPE_CONTEXT (ctx);
> > +  /* For functions peel the context up to namespace/TU scope.  The abstract
> > +     copies reveal the true nesting.  */
> > +  if (TREE_CODE (decl) == FUNCTION_DECL)
> > +    while (ctx && TREE_CODE (ctx) == FUNCTION_DECL)
> > +      ctx = DECL_CONTEXT (ctx);
> >    /* Likewise namespaces in case we do not want to emit DIEs for them.  */
> >    if (debug_info_level <= DINFO_LEVEL_TERSE)
> >      while (ctx && TREE_CODE (ctx) == NAMESPACE_DECL)
> > @@ -6099,8 +6104,7 @@ maybe_create_die_with_external_ref (tree decl)
> >         /* Leave function local entities parent determination to when
> >            we process scope vars.  */
> >         ;
> > -      else
> > -       parent = lookup_decl_die (ctx);
> > +      parent = lookup_decl_die (ctx);
> >      }
> >    else
> >      /* In some cases the FEs fail to set DECL_CONTEXT properly.
> >
>
> Thanks. This solves the problem. Only the first hunk was required. Second hunk
> actually causes an ICE when TREE_CODE (ctx) == BLOCK.
> OK to commit the attached patch?

I think we need to merge the TYPE_P peeling and FUNCTION_DECL peeling into
one loop since I suppose we can have a nested function in class scope.
So sth like

diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index 82783c4968b..61228410b51 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -6073,8 +6073,12 @@ maybe_create_die_with_external_ref (tree decl)
     }
   else
     ctx = DECL_CONTEXT (decl);
-  /* Peel types in the context stack.  */
-  while (ctx && TYPE_P (ctx))
+  /* Peel types in the context stack.  For functions peel the context up
+     to namespace/TU scope.  The abstract copies reveal the true nesting.  */
+  while (ctx
+        && (TYPE_P (ctx)
+            || (TREE_CODE (decl) == FUNCTION_DECL
+                && TREE_CODE (ctx) == FUNCTION_DECL)))
     ctx = TYPE_CONTEXT (ctx);
   /* Likewise namespaces in case we do not want to emit DIEs for them.  */
   if (debug_info_level <= DINFO_LEVEL_TERSE)

if that works it's OK.  Can you run it on the gdb testsuite with -flto added
as well please (you need to do before/after comparison since IIRC adding
-flto will add a few fails).

Thanks,
Richard.