This commit fixes the DPP sequence in the atomic optimizer (which was
previously missing the row_shr:3 step), and works around a read_register
exec bug by using a ballot instead.
Differential Revision: https://reviews.llvm.org/D57737
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@353703 91177308-0d34-0410-b5e6-96231b3b80d8
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
