llvm dev - Mar 2018 - [RFC] Generate Debug Information for Labels in Function

> Based on that I think it might be sufficient to have a flag on an IR label
> that marks a user-originated label and triggers the backend to create a
> DW_TAG_label for it. If we do need source location information for the
> DW_TAG_label, we could grab it from the first instruction.
Are there languages where labels are scoped?  If so we'd need explicit
metadata to identify the parent scope.  In C/C++ the only scope is the
containing function, which I'm guessing we wouldn't need to specify
(except for inlined functions? that might need some care to get right).

I feel compelled to point out that the top instructions in a block do not
necessarily have a valid source location so we might want to carry that
explicitly just for sanity's sake.
--paulr

> -----Original Message-----
> From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of via
> llvm-dev
> Sent: Thursday, March 29, 2018 1:54 PM
> To: aprantl at apple.com; hsiangkai at gmail.com
> Cc: llvm-dev at lists.llvm.org
> Subject: Re: [llvm-dev] [RFC] Generate Debug Information for Labels in
> Function
> 
> > Based on that I think it might be sufficient to have a flag on an IR
> label
> > that marks a user-originated label and triggers the backend to create
a
> > DW_TAG_label for it. If we do need source location information for the
> > DW_TAG_label, we could grab it from the first instruction.
> 
> Are there languages where labels are scoped?  If so we'd need explicit
> metadata to identify the parent scope.  In C/C++ the only scope is the
> containing function, which I'm guessing we wouldn't need to specify
> (except for inlined functions? that might need some care to get right).
> 
> I feel compelled to point out that the top instructions in a block do not
> necessarily have a valid source location so we might want to carry that
> explicitly just for sanity's sake.
That is, carry the source location explicitly on the label.
> --paulr
> 
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> On Mar 29, 2018, at 10:55 AM, paul.robinson at sony.com wrote:
> 
> 
> 
>> -----Original Message-----
>> From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of
via
>> llvm-dev
>> Sent: Thursday, March 29, 2018 1:54 PM
>> To: aprantl at apple.com; hsiangkai at gmail.com
>> Cc: llvm-dev at lists.llvm.org
>> Subject: Re: [llvm-dev] [RFC] Generate Debug Information for Labels in
>> Function
>> 
>>> Based on that I think it might be sufficient to have a flag on an
IR
>> label
>>> that marks a user-originated label and triggers the backend to
create a
>>> DW_TAG_label for it. If we do need source location information for
the
>>> DW_TAG_label, we could grab it from the first instruction.
>> 
>> Are there languages where labels are scoped?  If so we'd need
explicit
>> metadata to identify the parent scope.  In C/C++ the only scope is the
>> containing function, which I'm guessing we wouldn't need to
specify
>> (except for inlined functions? that might need some care to get right).
>> 
>> I feel compelled to point out that the top instructions in a block do
not
>> necessarily have a valid source location so we might want to carry that
>> explicitly just for sanity's sake.
> 
> That is, carry the source location explicitly on the label.
Thanks that's a good point. I still wonder what a debugger would do with the
source location of a label though? For setting breakpoints it seems redundant
with the location of the next instruction. Does GCC emit source location for a
label, or just its name? If yes, does GDB do anything with that information?

-- adrian