[X86] Warn if a scheduling instrs/instregex entry doesn't alter the default schedule

[RKSimon]

Bugzilla Link	35548
Version	trunk
OS	Windows NT
Depends On	#36479
Blocks	#31672
CC	@adibiagio,@legrosbuffle,@topperc,@rotateright

Extended Description

Scheduler model instregex entries only need to be added if they alter the behaviour of an instruction's default scheduling class/itinerary.

If the instregex is effectively useless, then tablegen should at least emit a debug warning reporting that.

[RKSimon]

This should also cover instrs, not just instregex

[llvmbot]

After some investigation I realised I don't understand the issue:
what is default scheduling class/itinerary?
could you show any example of wrong instregex and/or instrs?

In any case instregex uses WriteRes which "tuned" to CPU specific resource. Even if we have Latency = 1 we're using a new resource for every CPU that's why we simply can't keep "default" behaviour. Am I right?

Please, clarify when instregex/instrs could be "effectively useless".

[llvmbot]

OK, it seems I understood the issue - forget about my question.

[RKSimon]

mentioned in issue #36479