[m-rev.] ssdb v1.0 fixed

[Ian MacLarty]

On Wed, Dec 05, 2007 at 02:55:19PM +1100, Julien Fischer wrote:
>
>
>
> On Wed, 5 Dec 2007, Peter Wang wrote:
>
>> On 2007-12-05, Julien Fischer <juliensf at csse.unimelb.edu.au> wrote:
>>>>        I'm not sure where the ssdb transform should go. I assume as 
>>>> early
>>>> as
>>>> 	possible.
>>>
>>>  I think the opposite is probably true.

Can you explain your rationale?  I think earlier is better, because
generally user's don't want to debug code that's been transformed into
something unrecognisable (note that the target users of the debugger
should be Mercury users, not the compiler developers).

>>
>> One problem with doing that is that putting breakpoints on the original
>> procedures won't work reliably because earlier transformations may have
>> e.g. specialised that procedure and changed the call sites.  Which
>> practically means disabling all transformations that might affect the
>> user's view of the program if ssdb is enabled.
>
> Which is what mdb does.  I think trying to preserve the user's
> view of the program in the presence of program transformations is
> a fairly tall order.
>

Doing it early on would allow us to still apply later optimisations
(which would hopefully speed up the debugger a little bit).  Later
optimisations shouldn't affect the behaviour of the debugger, because
the should respect the impurity annotations of the debugger-transformed
code.

Ian.
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