Address feedback in https://reviews.llvm.org/D133637
https://reviews.llvm.org/D133637 fixes the problem where we should hash raw content of
register mask instead of the pointer to it.
Fix the same issue in `llvm::hash_value()`.
Remove the added API `MachineOperand::getRegMaskSize()` to avoid potential confusion.
Add an assert to emphasize that we probably should hash a machine operand iff it has
associated machine function, but keep the fallback logic in the original change.
Reviewed By: MatzeB
Differential Revision: https://reviews.llvm.org/D133747