TwoAddressInstructionPass refactoring: Extract a method.

No functional change intended, except replacing a DenseMap with a
SmallDenseMap which should behave identically.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161281 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed