NewGVN: Fix PR32838.
This is a complicated bug involving two issues:
1. What do we do with phi nodes when we prove all arguments are not
live?
2. When is it safe to use value leaders to determine if we can ignore
an argumnet?

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@303453 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed