AMDGPU/SI: Add a MachineMemOperand to MIMG instructions

Summary:
Without a MachineMemOperand, the scheduler was assuming MIMG instructions
were ordered memory references, so no loads or stores could be reordered
across them.

Reviewers: arsenm

Subscribers: arsenm, kzhuravl, wdng, nhaehnle, yaxunl, tony-tye

Differential Revision: https://reviews.llvm.org/D27536

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290179 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed