[llvm] [VPlan] Use target's index type for {First,Last}ActiveLane instead of i64 (PR #186361)

[Florian Hahn via llvm-commits]

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@@ -45,6 +45,7 @@ class VPTypeAnalysis {
   /// any underlying IR value (like the vector trip count or the backedge-taken
   /// count).
   Type *CanonicalIVTy;
+  Type *IndexTy;
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fhahn wrote:

do we need to sore in context just for 2 recipes? Seems fairly cheap to determine inline?

If w want to keep this member, would be good to document

https://github.com/llvm/llvm-project/pull/186361