[NewGVN] Stop assuming PHI args ordering when looking at phi-of-ops.

It's not guaranteed. There's a bug open to sort them in predecessor
order, but it won't happen anytime soon. In the meanwhile, passes
will have to do an O(#preds) scan. Such is life.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@316953 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed