[llvm-dev] Why LLVM doesn't have debug information of function right parentheses？

[Robinson, Paul via llvm-dev]

> -----Original Message-----
> From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Simon
> Cook via llvm-dev
> Sent: Thursday, August 03, 2017 11:06 AM
> To: llvm-dev at lists.llvm.org
> Subject: Re: [llvm-dev] Why LLVM doesn't have debug information of
> function right parentheses？
> 
> 
> I have implemented this exact behavior in an out of tree LLVM fork I
> maintain, where one of my users needed this behavior, and it seems to
> work well. What we have done is extend the definition of DISubprogram to
> contain a new field "endLine" which holds the line number of the closing
> brace. A pass late in our backend uses this information to set the
> DebugLoc of return instructions in our programs.

Interesting.  I'd have thought the front end could generate the
return-value expression with the source location of the expression,
and the return instruction itself with source location of the closing
brace.  Then it would automatically apply to all targets (and all
debug-info formats).

Or, if that distinction got lost during some optimization, the
separate source location could be attached during instruction
selection?  Hopefully that could also be done in a target-neutral
way.
--paulr

> 
> I haven't yet tidied up and submitted this upstream for review, as
> without a consumer of this information, the extension itself is rather
> dead, but could if some backends would find that information useful and
> make use of it.
> 
> Thanks,
> Simon
> 
> On 03/08/17 15:13, Robinson, Paul via llvm-dev wrote:
> > I've had this request from my users as well, but it has never been high
> > enough on the priority list to look at closely.
> >
> > I think it would be feasible to have the actual ret instruction
> > associated with the closing brace, while the load/computation of the
> > return value would be associated with the `return` statement; but that's
> > as far as I got when I looked at this before.
> >
> > --paulr
> >
> >
> >
> > P.S. The word "parenthesis" plural "parentheses" refers specifically to
> > these characters: ( )
> >
> > Generally [ ] are "square brackets" or sometimes just "brackets" while {
> > } are called "braces" or "curly brackets."
> >
> >
> >
> > *From:*llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of
> > *Frozen via llvm-dev
> > *Sent:* Wednesday, August 02, 2017 11:19 PM
> > *To:* llvm-dev at lists.llvm.org
> > *Subject:* [llvm-dev] Why LLVM doesn't have debug information of
> > function right parentheses？
> >
> >
> >
> > Simple Case:
> >
> > 1.int main()
> > 2.{
> > 3.   int i = 0;
> > 4.   return 0;
> > 5.}
> >
> > compile command: clang -g a.c
> >
> > In LLVM IR, we have one attribute named "scopeLine" to indicate the left
> > parentheses. But we don't have one attribute to indicate the right
> > parentheses (line 5 in this example).
> >
> > So if we use gdb to debug it:
> > (gdb) b main
> > Breakpoint 1 at 0x100005c8: file a.c, line 3.
> > (gdb) r
> > Breakpoint 1, main () at a.c:3
> > 3      int i = 0;
> > Missing separate debuginfos,
> > (gdb) n
> > 4      return 0;
> > (gdb) n
> > 0x00003fffb7db4580 in generic_start_main.isra.0
> > We can not stop at line 5.
> >
> > But GCC can stop at line 5
> > (gdb) b main
> > Breakpoint 1 at 0x100005e0: file a.c, line 3.
> > (gdb) r
> > Breakpoint 1, main () at a.c:3
> > 3      int i = 0;
> > Missing separate debuginfos
> > (gdb) n
> > 4      return 0;
> > (gdb) n
> > 5    }
> > (gdb)
> >
> >
> >
> >
> >
> >
> >
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