[meta][x86] Improve scheduler classes instruction coverage

[RKSimon]

Bugzilla Link	36908
Resolution	FIXED
Resolved on	Feb 02, 2020 05:50
Version	trunk
OS	Windows NT
Depends On	#32204 #34956 #36229 #36257 #36259 #36272 #36278 #36279
Blocks	#31672

Extended Description

We've tended to avoid introducing too many scheduler classes, especially as not all targets need to support them [Bug #​35608].

However, we could considerably reduce the number of custom InstRW entries if we were smarter about the instructions attached to each class - adding/splitting classes, etc.

[RKSimon]

Resolving - we've done a lot of cleanup of the x86 schedule classes over the past 2 years, and SubtargetEmitter/CodeGenSchedModels warns for inefficient use of regex etc.

[RKSimon]

mentioned in issue #36257

[RKSimon]

mentioned in issue #36259

[RKSimon]

mentioned in issue #36272

[RKSimon]

mentioned in issue #36278

[RKSimon]

mentioned in issue #36279