[llvm-commits] [llvm] r169218 - in /llvm/trunk: include/llvm/ lib/CodeGen/AsmPrinter/ lib/VMCore/ test/CodeGen/ARM/ test/CodeGen/Thumb/ test/CodeGen/X86/ test/DebugInfo/ test/DebugInfo/X86/ test/JitListener/

[Bill Wendling]

On Dec 6, 2012, at 8:33 AM, David Blaikie <dblaikie at gmail.com> wrote:

>> why don't you emit it?  If the front-end produced it, shouldn't you just
>> output
>> it?
> 
> Yeah, this was sort of my thinking. The issue is that there's no way
> for the frontend /not/ to emit it in the current debug info LLVM
> metadata schema. And no nice way to make that field alone optional.
> (also: this would make frontends even more DWARF/debugger specific as
> they would be encoding knowledge of the defaults that are shared with
> debuggers - this could be a problem if we ever wanted to produce other
> debug info formats that had different, or nonexistent, defaults)
> 
>> Or is this basically a compression scheme to reduce the size of object
>> files?
> 
> Yes, that's the only reason to omit it - reducing the size of debug
> info data produced in the end.
> 
That's my guess too.

>> This is wrong for Ada, which defaults to '1' as the lower bound of an
>> array.
>> 
>> There isn't really a default specified by the Ada language itself.  However
>> I
>> guess what matters is what gdb/lldb thinks the lower bound is if there is no
>> explicit lower bound.  Did anyone rummage around inside the debuggers to
>> determine that?
> 
> Not sure - I believe the DWARF spec has some suggestions, but I'm not
> sure if Bill took that or other data to make the determination.
> 
I looked at the DWARF spec and it specified 1 as the default for Ada, Fortran, and friends.

-bw