Now that we have operand info for machine instructions, use it to create

Now that we have operand info for machine instructions, use it to create
temporary registers for things that define a register.  This allows dag->dag
isel to compile this:

int %test() { ret int 65535 }

into:

_test:
        lis r2, 0
        ori r2, r2, 65535
        blr

Next up, getting CopyFromReg to work, allowing arguments and cross-bb values.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22932 91177308-0d34-0410-b5e6-96231b3b80d8