llvm dev - Aug 2017 - 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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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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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.

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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