fix a bug where we had an implicit assumption that the

fix a bug where we had an implicit assumption that the
result instruction operand numbering matched the result pattern.

Fixing this allows us to move the xchg/test aliases to the .td file.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@118334 91177308-0d34-0410-b5e6-96231b3b80d8