[X86] Split WriteIMul into 8/16/32/64 implementations

[RKSimon]

Bugzilla Link	36931
Resolution	FIXED
Resolved on	Sep 24, 2018 08:57
Version	trunk
OS	Windows NT
Depends On	#35432
Blocks	#31672 #35898 #36479 #36256
CC	@alexey-bataev,@adibiagio,@legrosbuffle,@topperc,@rotateright
Fixed by commit(s)	rL331770, rL342892

Extended Description

MUL64 definitely needs its own scheduler class, possibly the others as well. Multiply by constant (IMUL32rmi etc.) may need splitting off as well.

Note: Integer multiplies seem to be a common issue in vectorization regressions (incorrectly comparing scalar/vector integer multiply costs), so all need to be accurate for [Bug #​36550] to work well.

[RKSimon]

assigned to @RKSimon

[RKSimon]

rL331770 split off WriteIMul for i64 multiplies.

Note: I haven't set this up for all models yet - there are a lot of models that are missing some versions (IMUL64rri32 etc.) that need cleaning up first.

[RKSimon]

rL342892 splits WriteIMul by size and also by IMUL multiply-by-imm and multiply-by-reg cases, removing all overrides in the scheduler models.

[RKSimon]

mentioned in issue #36479