[llvm] [SLP] Use named structs in vectorizeStores() (NFC) (PR #132781)

[Gaëtan Bossu via llvm-commits]

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@@ -884,6 +884,42 @@ class InstructionsState {
   static InstructionsState invalid() { return {nullptr, nullptr}; }
 };
 
+/// A reference to a ld/st instruction and the distance of its address to a base
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gbossu wrote:

Is there really no code that can be shared? I see `getPointersDiff` is also used in the logic for vectorizing loads

https://github.com/llvm/llvm-project/pull/132781