transformations in target-specific DAG combines without causing DAGCombiner to
delete the same node twice. If you know of a better way to avoid this (see my
next patch for an example), please let me know.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128758 91177308-0d34-0410-b5e6-96231b3b80d8