[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/

[Eric Christopher]

On Wed, Dec 5, 2012 at 11:45 AM, Bill Wendling <wendling at apple.com> wrote:

> On Dec 5, 2012, at 11:40 AM, David Blaikie <dblaikie at gmail.com> wrote:
>
> > On Wed, Dec 5, 2012 at 11:29 AM, Eric Christopher <echristo at gmail.com>
> wrote:
> >> On Wed, Dec 5, 2012 at 11:25 AM, Bill Wendling <isanbard at gmail.com>
> wrote:
> >>>
> >>> On Dec 5, 2012, at 11:07 AM, Eric Christopher <echristo at gmail.com>
> wrote:
> >>>
> >>>>> Awesome. FWIW we're probably getting those cases wrong in debug info
> >>>>> :)
> >>>>>
> >>>> We're definitely getting the negative lower bounds wrong, since the
> >>>> value's retrieved as a uint64_t. The zero case will be omitted for
> Ada and
> >>>> friends.
> >>>>
> >>>> Agreed. If you'd like to fix it that'd be awesome, if not file a bug
> and
> >>>> I'll get to it eventually.
> >>>>
> >>> Okay. The fix is to emit the lower bound in all cases. I don't think
> this
> >>> will be a problem for the debugger. It just adds extra information that
> >>> it'll probably ignore in C/C++. :)
> >>
> >>
> >> No, it's not. The correct is to omit it when the lower bound is the
> same as
> >> the default lower bound which I just gave in this thread :)
> >
> > (I'm not sure I'm helping here, but I'm confused as to the degree of
> > talking-past that's gone on with this issue... hopefully I'm doing
> > more good than harm)
> >
> > Frontends (Clang, DragonEgg, etc) know which language they're emitting
> > debug info for & what the default is. They emit lower bounds whenever
> > the bound is not the language-specific default.
> > Backend (LLVM) unconditionally emits whatever the frontend gave it.
> >
> > & thus we get the minimum required debug info: values when they're not
> > the default, relying on the default when it matches.
> >
> Here's my problem. Let's say that Ada is using an array that starts at
> '0'. Right now, we treat a lower bound of '0' as the default for the
> language (because we're assuming C/C++ here) and we won't emit it in the
> DWARF. This is wrong for Ada, which defaults to '1' as the lower bound of
> an array. Conversely, we *will* emit a lower bound for Ada if it says that
> the lower bound is '1', since we don't expect that to be the default.
> Emitting a lower bound of '1' is not needed here, of course.
>
> I just need a way of determining if the lower bound given to us is the
> default for the source language or not. If it's not, then we will emit the
> lower bound attribute. Otherwise, we won't.
>

It's pretty simple, the compile unit has the source language (look for
AT_language) or Language in DwarfCompileUnit.h, basically we'll need a
small function that checks the value of language and switches on that and
the "known defaults" as to when we'd want to emit it.

-eric
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20121205/1cfc7665/attachment.html>