More changes for non-top-down fast-isel.

More changes for non-top-down fast-isel.

Split the code for materializing a value out of
SelectionDAGBuilder::getValue into a helper function, so that it can
be used in other ways. Add a new getNonRegisterValue function which
uses it, for use in code which doesn't want a CopyFromReg even
when FuncMap.ValueMap already has an entry for it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106422 91177308-0d34-0410-b5e6-96231b3b80d8