[m-rev.] for review: Implement unify/compare of tuples in Mercury.

[Julien Fischer]

Hi Peter,

I haven't had time to review this fully, but there's one rather obvious
thing wrong with.  In principle the change is fine by me -- can you now
deep profile prince?

On Mon, 7 Jul 2014, Peter Wang wrote:

> Branches: master
>
> The hand-written C unify and compare predicates for tuples did not preserve
> deep profiler invariants correctly across the recursive unify/compare of
> tuple arguments.  I tried to do so, and failed.  Instead, implement the
> predicates in Mercury so the compiler can perform the deep profiling
> transformation on them.  Bug #3.
>
> A micro-benchmark on my machine is about twice as fast in asm_fast.gc
> after this patch, and equally fast in hlc.gc.  The change to the
> high-level C backend is only to reduce code duplication.
>
> I seem to have hit an unrelated bug in compare_representation so I did
> not implement the compare_representation predicate for tuples yet.
>
> library/builtin.m:
> 	Add `unify_tuple' and `compare_tuple' predicates.
>
> 	Add module initialisation predicate which sets
> 	`MR_special_pred_hooks' to point to those predicates.

That won't work.  You need to ensure that they are registered *before*
any user code (such as module local initialisers) can be called.  So the
right way to do it is as part of io.init_state.

Cheers,
Julien.