Why is this a SetVector?
I think this won't work in the case where the operand itself has a subregister.
%0:vreg_64 = REG_SEQUENCE %vreg_64.sub0, sub1, %vreg_64.1, sub0
I think you can use composeSubRegIndices here
No else after continue
It cannot directly happen because we are in SSA and def must be a result of mov_dpp, i.e. defining the whole register.
What's wrong with it? A register either has def or not. The other way would be to keep all reg_sequences along with the info about all subregs, if they were combined or not.
That is not necessarily a mov anymore, it can be a reg_sequence operand now. But I guess this is part of older patch, because all reg_sequences are processed inside this function now. I probably need to remove it.