Fix PR 49014

[Andrey Belevantsev]

On 25.05.2011 18:41, Bernd Schmidt wrote:
>
> On 05/25/2011 08:21 AM, Andrey Belevantsev wrote:
>> Vlad, Bernd, I wonder if we can avoid having recog_memoized>=0 insns
>> that do not have proper DFA reservations (that is, they do not change
>> the DFA state).  I see that existing practice allows this as shown by
>> Bernd's patch to 48403, i.e. such insns do not count against
>> issue_rate.  I would be happy to fix sel-sched in the same way.
>> However, both sel-sched ICEs as shown by PRs 48143 and 49014 really
>> uncover the latent bugs in the backend.  So, is it possible to stop
>> having such insns if scheduling is desired, or otherwise distinguish the
>> insns that wrongly miss the proper DFA reservation?
>
> Add a bool target podhook, targetm.sched.all_insns_have_reservations,
> and add an assert in the scheduler if it is true.
>
> I'm not sure what a good default value would be. Defining it to true
> would almost certainly break a few ports initially (even assuming we
> override it in sh where it's known not to be true), but I guess it such
> an assertion failure would be useful information for the target maintainers.
I think the hook is a better idea than the attribute because nobody will 
care to mark all offending insns with an attribute.  However, I must take a 
look to see how much work should be done for x86-64 to make the hook return 
true by default.  I didn't get even past the very first libgcc build with 
this assert enabled.

Andrey

>
> Or, if we want to enable extra checking on ports where not all insns
> have a reservation, a new insn attribute ("has_reservation") could be
> defined, defined to evaluate to true by default in genattrtab, and
> (set_attr "has_reservation" "0") added in the machine descriptions where
> necessary.
>
>
> Bernd