[VPlan] Group together helpers for retrieving various VPBlocks (NFCI).

Group together functions to retrieve various blocks of a VPlan, as
suggested in #114292.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -3825,12 +3825,17 @@ class VPlan {
   VPBasicBlock *getEntry() { return Entry; }
   const VPBasicBlock *getEntry() const { return Entry; }
 
-  /// Return the VPIRBasicBlock wrapping the header of the scalar loop.
-  VPIRBasicBlock *getScalarHeader() const { return ScalarHeader; }
+  /// Returns the preheader of the vector loop region.
+  VPBasicBlock *getVectorPreheader() {
+    return cast<VPBasicBlock>(getVectorLoopRegion()->getSinglePredecessor());
+  }
 
-  /// Return the VPBasicBlock for the preheader of the scalar loop.
-  VPBasicBlock *getScalarPreheader() const {
-    return cast<VPBasicBlock>(ScalarHeader->getSinglePredecessor());
+  /// Returns the VPRegionBlock of the vector loop.
+  VPRegionBlock *getVectorLoopRegion() {
+    return cast<VPRegionBlock>(getEntry()->getSingleSuccessor());
+  }
+  const VPRegionBlock *getVectorLoopRegion() const {
+    return cast<VPRegionBlock>(getEntry()->getSingleSuccessor());
   }
 
   /// Returns the 'middle' block of the plan, that is the block that selects
@@ -3843,6 +3848,14 @@ class VPlan {
     return cast<VPBasicBlock>(getVectorLoopRegion()->getSingleSuccessor());
   }
 
+  /// Return the VPBasicBlock for the preheader of the scalar loop.
+  VPBasicBlock *getScalarPreheader() const {
+    return cast<VPBasicBlock>(ScalarHeader->getSinglePredecessor());
+  }
+
+  /// Return the VPIRBasicBlock wrapping the header of the scalar loop.
+  VPIRBasicBlock *getScalarHeader() const { return ScalarHeader; }
+
   /// Return an iterator range over the VPIRBasicBlock wrapping the exit blocks
   /// of the VPlan, that is leaf nodes except the scalar header. Defined in
   /// VPlanHCFG, as the definition of the type needs access to the definitions
@@ -3953,19 +3966,6 @@ class VPlan {
   LLVM_DUMP_METHOD void dump() const;
 #endif
 
-  /// Returns the VPRegionBlock of the vector loop.
-  VPRegionBlock *getVectorLoopRegion() {
-    return cast<VPRegionBlock>(getEntry()->getSingleSuccessor());
-  }
-  const VPRegionBlock *getVectorLoopRegion() const {
-    return cast<VPRegionBlock>(getEntry()->getSingleSuccessor());
-  }
-
-  /// Returns the preheader of the vector loop region.
-  VPBasicBlock *getVectorPreheader() {
-    return cast<VPBasicBlock>(getVectorLoopRegion()->getSinglePredecessor());
-  }
-
   /// Returns the canonical induction recipe of the vector loop.
   VPCanonicalIVPHIRecipe *getCanonicalIV() {
     VPBasicBlock *EntryVPBB = getVectorLoopRegion()->getEntryBasicBlock();