1) With X86 lowering change, the following can no longer happen since

   the branch's chain is also produced by cmp.
          [ch, r : ld]
             ^ ^
             | |
      [XX]--/   \- [flag : cmp]
       ^             ^
       |             |
       \---[br flag]-

Remove an isel check which prevents loads from being folded into cmp / test
instructions.

2) Whenever possible, delete a selected node to allow more load folding
opportunities. Note not all nodes can be deleted after it has been
selected. Some may have simply morphed; some have not changed at all (e.g.
EntryToken).

llvm-svn: 30242