[llvm] [SLP] Split blocking build-vector stores in scalar chains (PR #194970)

[Yaxun Liu via llvm-commits]

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@@ -2241,7 +2221,7 @@ class slpvectorizer::BoUpSLP {
   }
 
   /// Returns true if the tree is a reduction tree.
-  bool isReductionTree() const { return UserIgnoreList != nullptr; }
+  bool isReductionTree() const { return IsReductionTree; }
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yxsamliu wrote:

Good point. The IsReductionTree flag is gone in the rebased stack. The new commits use UserIgnoreList directly under a store reduction framing: the original insertelement chain plus the original StoreInsts play the role of the reduction-operation chain, and they go straight into UserIgnoreList. There is no separate flag and no new TreeEntry state added for this path.

https://github.com/llvm/llvm-project/pull/194970