[llvm] [VPlan] Introduce VPlan-based hasTailFolded helper. (NFC) (PR #208329)

[Luke Lau via llvm-commits]

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@@ -4894,6 +4894,12 @@ class VPlan {
   /// loop region contains a nested loop region.
   LLVM_ABI_FOR_TEST bool isOuterLoop() const;
 
+  /// Returns true if the vector loop region is tail-folded.
+  bool hasTailFolded() const {
+    const VPRegionBlock *LoopRegion = getVectorLoopRegion();
+    return LoopRegion && LoopRegion->getHeaderMask();
+  }
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lukel97 wrote:

I forgot, the header mask is now a symbolic value. And it will stick around after `VPlanTransforms::materializeHeaderMask`, even if the materialized mask is removed

https://github.com/llvm/llvm-project/pull/208329