[Dominators] Add PDT constructor from Function

Summary: This patch adds a PDT constructor from Function and lets codes previously using a local class to do this use PostDominatorTree class directly.

Reviewers: davide, kuhar, grosser, dberlin

Reviewed By: kuhar

Author: NutshellySima

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D46709

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@333102 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed