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

[Joseph Huber via Phabricator via llvm-commits]

jhuber6 added a comment.

In D151341#4380694 <https://reviews.llvm.org/D151341#4380694>, @nhaehnle wrote:

> 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.

We have a similar check for that explicit case in the `OpenMPOpt` pass https://github.com/llvm/llvm-project/blob/main/llvm/lib/Transforms/IPO/OpenMPOpt.cpp#L2760.


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