[PATCH] D147408: [AMDGPU] Enable AMDGPU Atomic Optimizer Pass by default.

[Jay Foad via Phabricator via llvm-commits]

foad added a comment.

> Scalar branches may be the most expensive aspect of this algorithm

If not-taken conditional branches are cheap then we could do something like this. It only has one taken branch, when we have finished handling all the active lanes.

    // Inclusive plus-scan v0 into v1. Also leaves the result of the plus-reduction in s3.
    s_mov s0, exec
    s_mov s3, 0 // accumulator
  // repeat this section 32 or 64 times:
    s_ff1 s1, s0 // find lowest remaining active lane
    s_cmp_eq s1, -1
    s_cbranch_scc1 end
    s_bitset0 s0, s1
    v_readlane s2, v0, s1
    s_add s3, s2
    v_writelane v1, s3, s1
  // end of repeated section
  end:


Repository:
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  https://reviews.llvm.org/D147408/new/

https://reviews.llvm.org/D147408