[llvm] [LoopVectorizer] Prune VFs based on plan register pressure (PR #132190)

[David Sherwood via llvm-commits]

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@@ -4885,8 +4872,248 @@ void LoopVectorizationCostModel::collectElementTypesForWidening() {
   }
 }
 
+/// Estimate the register usage for \p Plan and vectorization factors in \p VFs.
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david-arm wrote:

Is it necessary to move this function? It makes it a lot more difficult to review. If it can't be avoided then perhaps it should be moved in a separate NFC commit within the same PR or done in a different PR?

https://github.com/llvm/llvm-project/pull/132190