TableGen: Support lanemasks for classes without subregisters
Previously using lanemasks on registers without any subregisters was not
well defined. This commit extends TargetRegisterInfo/tablegen to:
- Report a lanemask of 1 for regclasses without subregisters
- Do the right thing when mapping a 0/1 lanemask from a class without
subregisters into a class with subregisters in
TargetRegisterInfo::composeSubRegIndexLaneMasks().
This will be used in the upcoming "DetectDeadLanes" patch.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267848
91177308-0d34-0410-b5e6-
96231b3b80d8