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

[Hafiz Abid Qadeer]

On 19/07/2021 11:45, Richard Biener wrote:
> 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)
> 
This causes an ICE,
internal compiler error: tree check: expected class 'type', have 'declaration' (function_decl)

Did you intend something like this:

diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index 561f8b23517..c61f0041fba 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -6121,3 +6121,8 @@ maybe_create_die_with_external_ref (tree decl)
-  /* Peel types in the context stack.  */
-  while (ctx && TYPE_P (ctx))
-    ctx = TYPE_CONTEXT (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_P (ctx) ? TYPE_CONTEXT (ctx) : DECL_CONTEXT (ctx);
+


> 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.
> 


-- 
Hafiz Abid Qadeer
Mentor, a Siemens Business