[llvm] [VPlan] Replace VPRegionBlock with explicit CFG before execute (NFCI). (PR #117506)

[Alexey Bataev via llvm-commits]

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@@ -3958,9 +4006,7 @@ class VPlan {
   }
 
   /// Returns the preheader of the vector loop region.
-  VPBasicBlock *getVectorPreheader() {
-    return cast<VPBasicBlock>(getVectorLoopRegion()->getSinglePredecessor());
-  }
+  VPBasicBlock *getVectorPreheader() { return cast<VPBasicBlock>(getEntry()); }
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alexey-bataev wrote:

```suggestion
  VPBasicBlock *getVectorPreheader() const { return cast<VPBasicBlock>(getEntry()); }
```


https://github.com/llvm/llvm-project/pull/117506