[InlineCost] Tracking Values through PHI Nodes

This patch fix this FIXME in visitPHI()

FIXME: We should potentially be tracking values through phi nodes,
especially when they collapse to a single value due to deleted CFG edges
during inlining.

Differential Revision: https://reviews.llvm.org/D38594

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@320699 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed