Remove the TRI::getSubRegisterRegClass() hook.
This restores my karma after I added TRI::getSubClassWithSubReg().
Register constraints are applied 'backwards'. Starting from the
register class required by an instruction operand, the correct question
is: 'How can I constrain the super-register register class so all its
sub-registers satisfy the instruction constraint?' The
getMatchingSuperRegClass() hook answers that.
We never need to go 'forwards': Starting from a super-register register
class, what register class are the sub-registers in? The
getSubRegisterRegClass() hook did that.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141258
91177308-0d34-0410-b5e6-
96231b3b80d8