[TwoAddressInstructionPass] Replace subregister uses when processing tied operands

Summary:
TwoAddressInstruction pass typically rewrites
  %1:short = foo %0.sub_lo:long
as
  %1:short = COPY %0.sub_lo:long
  %1:short = foo %1:short
when having tied operands.

If there are extra un-tied operands that uses the same reg and
subreg, such as the second and third inputs to fie here:
  %1:short = fie %0.sub_lo:long, %0.sub_hi:long, %0.sub_lo:long
then there was a bug which replaced the register %0 also for
the un-tied operand, but without changing the subregister indices.
So we used to get:
  %1:short = COPY %0.sub_lo:long
  %1:short = fie %1, %1.sub_hi:short, %1.sub_lo:short
With this fix we instead get:
  %1:short = COPY %0.sub_lo:long
  %1:short = fie %1, %0.sub_hi:long, %1

Reviewers: arsenm, JesperAntonsson, kparzysz, MatzeB

Reviewed By: MatzeB

Subscribers: bjope, kparzysz, wdng, llvm-commits

Differential Revision: https://reviews.llvm.org/D36224

llvm-svn: 344492