[m-dev.] not_reached inst

Simon Taylor staylr at gmail.com
Wed Apr 11 14:43:31 AEST 2007

On 11-Apr-2007, Ian MacLarty <maclarty at csse.unimelb.edu.au> wrote:
> I've been reading David Overton's PHD thesis and discovered the not_reached
> inst.
> I would find it useful to use this inst in some Mercury code that is being
> automatically generated.  The not_reached insts is however not documented
> anywhere in the reference manual.  Could we make the not_reached inst
> "official" by documenting it in the reference manual?  Are there any problems
> with using the not_reached inst in Mercury programs?

In what context do you want to use not_reached insts?  What would the
documented behaviour be?

My understanding is that not_reached insts are used internally by the compiler
to signal that the current program point is unreachable.  A single variable in
an instmap can't have a not_reached inst.  Either the instmap is reachable, and
no variables have a not_reached inst, or the instmap is unreachable and all
variables have a not_reached inst.  The instmap is made unreachable by a goal
with determinism failure or erroneous.

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