[llvm] [NaryReassociate] Teach NaryReassociate about UniformityAnalysis (PR #175167)

[Jim M. R. Teichgräber via llvm-commits]

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@@ -183,6 +184,7 @@ class NaryReassociatePass : public PassInfoMixin<NaryReassociatePass> {
   ScalarEvolution *SE;
   TargetLibraryInfo *TLI;
   TargetTransformInfo *TTI;
+  UniformityInfo *UI;
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J-MR-T wrote:

I'm not sure it will be of any use here, but we implemented a prototype for updatable uniformity analysis [here](https://github.com/J-MR-T/llvm-project/commit/f171f467659b4822305f6014d39484811efac7b6).

Unfortunately, I don't have time to continue the project at the moment. But if there are any questions, I'd be happy to answer them! 

One of the most fundamental problems making it hard to integrate into upstream is that it relies on a newly added way to register RAUW and Delete callbacks with values. While it has low overhead when unused, that overhead is not zero, and hard to measure as well.

https://github.com/llvm/llvm-project/pull/175167