[AMDGPU] detect WaW hazards when moving/merging load/store instructions

Summary:
    In order to combine memory operations efficiently, the load/store
    optimizer might move some instructions around. It's usually safe
    to move instructions down past the merged instruction because the
    pass checks if memory operations can be re-ordered.

    Though, the current logic doesn't handle Write-after-Write hazards.

    This fixes a reflection issue with Monster Hunter World and DXVK.

    v2: - rebased on top of master
        - clean up the test case
        - handle WaW hazards correctly

    Bugzilla: https://bugs.llvm.org/show_bug.cgi?id=40130

Original patch by Samuel Pitoiset.

Reviewers: tpr, arsenm, nhaehnle

Reviewed By: nhaehnle

Subscribers: ronlieb, arsenm, kzhuravl, jvesely, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye

Differential Revision: https://reviews.llvm.org/D61313

llvm-svn: 361008