[dragonegg PATCH] Fix debug info for std::nullptr_t

[Eric Christopher]

On Wed, Jun 26, 2013 at 1:34 PM, Peter Collingbourne <peter at pcc.me.uk> wrote:
> On Wed, Jun 26, 2013 at 07:29:36PM +0200, Duncan Sands wrote:
>> Hi Peter,
>>
>> On 26/06/13 01:59, Peter Collingbourne wrote:
>>> On Tue, Jun 25, 2013 at 04:57:38PM -0700, Peter Collingbourne wrote:
>>>> Hi,
>>>>
>>>> This fixes debug info emission for std::nullptr_t (previously it would crash).
>>>>
>>>> OK to commit?
>>>
>>> With patch this time.
>>
>> thanks.  How about getting the name from the type rather than assuming it is
>> nullptr_t?
>
> I don't think it's possible for the debug info for nullptr_t to
> be of any form other than a DW_TAG_unspecified_type with a name of
> "nullptr_t" -- at least there doesn't seem to be a way to get Clang
> to spit out something else.  (For that matter, it isn't clear to me
> why DIBuilder::createNullPtrType lets you specify the name.)  Eric?
>

The short answer is that DW_TAG_unspecified_type can be used for more
than just nullptr_t.

The long answer is:

"An unspecified (implicit, unknown, ambiguous or nonexistent) type is
represented by a debugging information entry with the tag
DW_TAG_unspecified_type. If a name has been given to the type, then
the corresponding unspecified type entry has a DW_AT_name attribute
whose value is a null-terminated string containing the name as it
appears in the source program. The interpretation of this debugging
information entry is intentionally left flexible to allow it to be
interpreted appropriately in different languages. For example, in C
and C++ the language implementation can provide an unspecified type
entry with the name “void” which can be referenced by the type
attribute of pointer types and typedef declarations for 'void' (see
Sections 0 and 5.3, respectively). As another example, in Ada such an
unspecified type entry can be referred to by the type attribute of an
access type where the denoted type is incomplete (the name is declared
as a type but the definition is deferred to a separate compilation
unit)."

-eric