[m-rev.] for review: Fix compiler abort during liveness detection.

[Julien Fischer]

Hi Peter,

On Wed, 4 Sep 2013, Peter Wang wrote:

> [I'm not certain of the fix]

Neither am I.

Do you know where the call to goal_info_get_post_births that is causing
the aborts is?  In particular, is it whne detect_deadness (i.e. stage 2
of of liveness analysis) is processing an if-then-else?

Cheers,
Julien.
>
> The compiler would abort during liveness detection on an if-then-else goal
> with an unreachable Then branch, due to the Then goal not having its
> liveness-related fields initialised.  Bug #51.
>
> compiler/liveness.m:
> 	    As above.
>
> tests/valid/Mercury.options:
> tests/valid/Mmakefile:
> tests/valid/bug51.m:
> 	    Add test case.
>
> NEWS:
> 	    Announce the change.