[llvm] [LV] Avoid bailing on SCEVUnknown in uniformity-rew (PR #160144)

[Ramkumar Ramachandra via llvm-commits]

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@@ -528,14 +528,6 @@ class SCEVAddRecForUniformityRewriter
     return SCEVRewriteVisitor<SCEVAddRecForUniformityRewriter>::visit(S);
   }
 
-  const SCEV *visitUnknown(const SCEVUnknown *S) {
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artagnon wrote:

Thanks a lot for the example, by the way: it is somewhat unfortunate that we're blocked on the SCEVUnknown of the load, behind which an SCEVAddRec is hiding. I wonder if we can still get the benefits of the patch by looking inside the SCEVUnknown, and asserting that it is uncomputable if it is an Instruction?

https://github.com/llvm/llvm-project/pull/160144