[InstCombine] Moving overflow computation logic from InstCombine to ValueTracking; NFC

Differential Revision: https://reviews.llvm.org/D46704

Change-Id: Ifabcbe431a2169743b3cc310f2a34fd706f13f02

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@332026 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed