[x86] Extract a helper function to compute the full addressing mode from
an x86 MachineInstr's operands. This will be super useful to fix some
bad atomics code in my next commit.

No functionality changed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264819 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed