[llvm] [LV] Use wide lane masks as the canonical form when tail-folding & interleaving (PR #209484)

[Kerry McLaughlin via llvm-commits]

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@@ -147,29 +150,33 @@ addVPLaneMaskPhiAndUpdateExitBranch(VPlan &Plan) {
   // TODO: Check if dropping the flags is needed.
   TopRegion->clearCanonicalIVNUW(CanonicalIVIncrement);
   DebugLoc DL = CanonicalIVIncrement->getDebugLoc();
-  // We can't use StartV directly in the ActiveLaneMask VPInstruction, since
-  // we have to take unrolling into account. Each part needs to start at
-  //   Part * VF
+  // We can't use StartV directly in the WideActiveLaneMask
+  // VPInstruction, since we have to take unrolling into account.
+  // Each part needs to start at Part * VF
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kmclaughlin-arm wrote:

I think `EntryIncrement` is still needed to make sure `ExtractVectorForPart` is unrolled correctly, but I've reworded the comment and moved it further down to where the instruction is created.

https://github.com/llvm/llvm-project/pull/209484