6738933: assert with base pointers must match with compressed oops enabled
Reviewed-by:

Loop opts attempts to clone loop invariant uses of loop varying values
into the loop exits but because the clones don't actually differ from
the original node GVN will simply recommon them. To deal with this it
removes the clones from the worklist. There's a special case in there
for loads because this causes assertion failures concerning the base
of AddPs. This special case needs to be extended to included DecodeN
since they also form the base of oop loads. If the cloning weren't so
blind it could make sure that the cloned AddPs kept the same base but
for now extending the special case is good enough.

Tested with dacapo.