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This commit adds a new IR level pass to the AMDGPU backend to perform atomic optimizations. It works by: - Running through a function and finding atomicrmw add/sub or uses of the atomic buffer intrinsics for add/sub. - If all arguments except the value to be added/subtracted are uniform, record the value to be optimized. - Run through the atomic operations we can optimize and, depending on whether the value is uniform/divergent use wavefront wide operations (DPP in the divergent case) to calculate the total amount to be atomically added/subtracted. - Then let only a single lane of each wavefront perform the atomic operation, reducing the total number of atomic operations in flight. - Lastly we recombine the result from the single lane to each lane of the wavefront, and calculate our individual lanes offset into the final result. Differential Revision: https://reviews.llvm.org/D51969 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@343973 91177308-0d34-0410-b5e6-96231b3b80d8
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