[PATCH] D92887: [LoopUnroll] Use llvm.experimental.noalias.scope.decl for duplicating noalias metadata as needed

[Alina Sbirlea via Phabricator via llvm-commits]

asbirlea added a comment.

My concern with this patch is in the iteration on all instructions in the blocks in `cloneAndAdaptNoAliasScopes` and `identifyNoAliasScopesToClone`. 
Perhaps for LoopUnroll is not an issue, if unroll cost model is taken into account before this (i.e. unroll doesn't happen for large BBs). But when doing loop rotate, this may explode for IRs with large BBs, so I'd say some measurements would be helpful here.
For loop rotate, which instructions are cloned from the header to the preheader is known at the callsite, so as to not iterate over the entire original preheader, but I'm not sure this is sufficient.



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Comment at: llvm/test/Transforms/PhaseOrdering/pr39282.ll:56
   ret void
 }
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Nit: CHECKs for MDNodes?


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