[m-dev.] logging proposal

[Mark Brown]

On 19-Mar-2006, Ian MacLarty <maclarty at cs.mu.OZ.AU> wrote:
> On 3/19/06, Mark Brown <mark at cs.mu.oz.au> wrote:
> > On 19-Mar-2006, Julien Fischer <juliensf at cs.mu.OZ.AU> wrote:
> > > But then how much latitude is the compiler going to have to optimize code
> > > containing debug goals?
> >
> > Good question.  The strictness of mdb's events is determined by the
> > `--trace-optimized' option.  Perhaps we shohuld go by this or something
> > similar.
> >
> > I think that, as with the current debug events, users would expect their
> > debugging goals to be strict.  If they want to observe the optimized version
> > of their program they can ask for it with a compiler option.
> >
> 
> I'm not really following this part of the discussion.  What's the
> issue here?

Sometimes it is more helpful to observe the unoptimized version of your
program to figure out why it is misbehaving, and sometimes it is more
helpful to observe the optimized version.  Mdb provides both, with the
former being default and the latter being selected by the
`--trace-optimized' option.  We will also provide both with this feature,
since the user can get the unoptimized version with `-O-1', for example,
or the optimized version with `-O5' and maybe `--trace-optimized'.

So I guess the issue is what the default should be: optimized or
unoptimized.  That is, should the trace level (or whatever) that selects
these events affect the set of optimizations that are done, like
`--trace deep' does?

> If the trace goals are enabled then they cannot be
> optimized away or reordered in the predicate they appear in.  If the
> predicate the trace goal appears in is optimized away by the compiler,
> then it is equivalent to true in the semantics of the object code and
> why would anyone write a pure predicate always equivalent to true?

They may have done so unwittingly.  Garbage-In-Garbage-Out is never a
good foundation for debugging tools -- people who write garbage are the
ones who will need debugging the most.  ;-)

Having said that, I don't feel strongly either way what the default
behaviour should be.

Cheers,
Mark.

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