[llvm] [AMDGPU] Add amdgpu-lower-special-lds pass to lower named-barrier LDS (PR #165692)

[Sameer Sahasrabuddhe via llvm-commits]

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+//===-- AMDGPULowerSpecialLDS.cpp -----------------------------------------===//
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ssahasra wrote:

I agree we don't want to say "special", but "barrier" is also not accurate because we will soon need to lower semaphores as well.

https://github.com/llvm/llvm-project/pull/165692