[PATCH] D151341: AMDGPU: Special case uniformity info for singlethreaded workitem IDs

[Nicolai Hähnle via Phabricator via llvm-commits]

nhaehnle added a comment.

This could be a top-level check in isSourceOfDivergence: if a source of divergence executes with a single lane, it de facto stops being a source of divergence.

But even beyond that: it is reasonably common to have compute shaders that do something like this:

  if (threadid == 0) {
    ...
  }

So it would be interesting to be able to handle this more generally in UniformityAnalysis, perhaps by having a callback that analyzes conditional branches and returns whether one side of the branch is entered by at most one lane.

Once that's the long-term goal, it seems plausible to me to make `isSingleLaneExecution(Function &)` a callback that is accessible to UniformityAnalysis, as opposed to querying it from isSourceOfDivergence.


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  https://reviews.llvm.org/D151341/new/

https://reviews.llvm.org/D151341