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

[via llvm-dev]

> -----Original Message-----
> From: aprantl at apple.com [mailto:aprantl at apple.com]
> Sent: Thursday, March 29, 2018 2:23 PM
> To: Robinson, Paul
> Cc: hsiangkai at gmail.com; llvm-dev at lists.llvm.org
> Subject: Re: [llvm-dev] [RFC] Generate Debug Information for Labels in
> Function
> 
> 
> 
> > 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

A GUI debugger might show the source text near the label definition.
Suppose the first code after the label is an inlined function call.
Using the instruction's location would take you to the source for the
inlined function, not to the label and the source for the call.
--paulr