[llvm] [VPlan] Remove loop region in optimizeForVFAndUF. (PR #108378)

[via llvm-commits]

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@@ -3845,9 +3843,8 @@ class VPlan {
   const VPBasicBlock *getEntry() const { return Entry; }
 
   /// Returns the preheader of the vector loop region.
-  VPBasicBlock *getVectorPreheader() {
-    return cast<VPBasicBlock>(getVectorLoopRegion()->getSinglePredecessor());
-  }
+  VPBasicBlock *getVectorPreheader();
+  VPBasicBlock *getVectorPreheader() const;
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ayalz wrote:

Worth extending the comment to explain that the vector preheader VPBB continues to exist beyond its vector loop region, when the latter is removed for having a single iteration.

https://github.com/llvm/llvm-project/pull/108378