[CodeGen] Use RegUnits to track register aliases (NFC)

Summary: Use RegUnits to track register aliases in PostRASink and AArch64LoadStoreOptimizer.

Reviewers: thegameg, mcrosier, gberry, qcolombet, sebpop, MatzeB, t.p.northover, javed.absar

Reviewed By: thegameg, sebpop

Subscribers: javed.absar, llvm-commits, kristof.beyls

Differential Revision: https://reviews.llvm.org/D45695

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@331066 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed