[m-rev.] for review: add ll_debug GC grade

[Julien Fischer]

On Wed, 7 Dec 2011, Ian MacLarty wrote:

> On Wed, Dec 7, 2011 at 11:04 AM, Julien Fischer
> <juliensf at csse.unimelb.edu.au> wrote:
>>
>> On Wed, 7 Dec 2011, Peter Ross wrote:
>>
>>> On 6 December 2011 20:29, Ian MacLarty <maclarty at csse.unimelb.edu.au>
>>> wrote:
>>>>
>>>> For review by Julien.
>>>>
>>>> Branches: main, 11.07
>>>>
>>>> Add a new GC grade for the .ll_debug Mercury grade.
>>>>
>>>> Previously the .ll_debug grade used the usual "gc" GC grade.  This was a
>>>> problem, because it meant that installing a .ll_debug grade would
>>>> overwrite the
>>>> libgc library with the unoptimised .ll_debug version, resulting in a
>>>> severe
>>>> performance loss for applications even if they weren't built in the
>>>> .ll_debug
>>>> grade.
>>>>
>>>> compiler/compile_target_code.m:
>>>>    Link against the ll_debug GC library if low-level debugging
>>>>    is enabled.
>>>>
>>>> scripts/ml.in:
>>>>    Use the new ll_debug GC grade for the .ll_debug Mercury
>>>>    grades.
>>>>
>>> Maybe the ll_debug grade should imply the gcd grade?  Rather than
>>> installing a new version of the gc library.
>>
>>
>> I disagree.  I use the ll_debug grade quite a bit for debugging programs
>> written in the hlc grade that make heavy use of the C foreign code.
>> I have nver required the gcd grades for this; outside of debugging
>> interactions between the collector and the rest of the system I think
>> they are of too limited use.
>
> But would it hurt to use the .gcd version of boehm in ll_debug grades?
> In ll_debug grades C optimizations are already turned off, so what
> difference will also disabling NO_DEBUGGING in boehm make?

I'm not sure what the additional effects of adding disabling NO_DEBUGGING
are.  I know that doing so will enable code within the collector that is
intended for debugging the collector.

> It just seems a bit confusing to have two debug versions of the GC library.

Who will it confuse?  The circumstances in which the gcd version is
actually needed (or even installed) are very rare.

> What about the following solution:
> - Make the .gcd Mercury grade component also imply -g -O0 when building boehm.
> - Make the .ll_debug Mercury grade component turn off -DNO_DEBUGGING in boehm.
> (So boehm is built the same way if we're using either .ll_debug or
> .gcd mercury grade components).
> - Make the .ll_debug Mercury grade component imply the gc_debug GC
> grade component (i.e. make it use the .gcd version of boehm).

I think it is a solution to a problem that doesn't exist in the first
place.  Just add the ll_debug component for the .ll_debug grades and be
done with it.

Julien.