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

[Alexey Bataev via llvm-commits]

================
@@ -3543,6 +3585,8 @@ class VPBasicBlock : public VPBlockBase {
     return NewBlock;
   }
 
+  bool isHeader() { return any_of(phis(), IsaPred<VPHeaderPHIRecipe>); }
----------------
alexey-bataev wrote:

```suggestion
  bool isHeader() const { return any_of(phis(), IsaPred<VPHeaderPHIRecipe>); }
```


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