[Pipeliner] Fix in the pipeliner phi reuse code

When the definition of a phi is used by a phi in the next iteration,
the pipeliner was assuming that the definition is processed first.
Because of the assumption, an incorrect phi name was used. This patch
has a check to see if the phi definition has been processed already.

Patch by Brendon Cahoon.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@328510 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed