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

[Alexey Bataev via llvm-commits]

================
@@ -1032,51 +1047,55 @@ void VPlan::execute(VPTransformState *State) {
   for (VPBlockBase *Block : vp_depth_first_shallow(Entry))
     Block->execute(State);
 
-  VPBasicBlock *LatchVPBB = getVectorLoopRegion()->getExitingBasicBlock();
-  BasicBlock *VectorLatchBB = State->CFG.VPBB2IRBB[LatchVPBB];
-
   // Fix the latch value of canonical, reduction and first-order recurrences
   // phis in the vector loop.
-  VPBasicBlock *Header = getVectorLoopRegion()->getEntryBasicBlock();
-  for (VPRecipeBase &R : Header->phis()) {
-    // Skip phi-like recipes that generate their backedege values themselves.
-    if (isa<VPWidenPHIRecipe>(&R))
+  for (VPBasicBlock *Header :
+       VPBlockUtils::blocksOnly<VPBasicBlock>(vp_depth_first_shallow(Entry))) {
+    if (!Header->isHeader())
       continue;
+    for (VPRecipeBase &R : Header->phis()) {
+      VPBasicBlock *LatchVPBB =
+          cast<VPBasicBlock>(Header->getPredecessors()[1]);
+      BasicBlock *VectorLatchBB = State->CFG.VPBB2IRBB[LatchVPBB];
 
-    if (isa<VPWidenPointerInductionRecipe>(&R) ||
-        isa<VPWidenIntOrFpInductionRecipe>(&R)) {
-      PHINode *Phi = nullptr;
-      if (isa<VPWidenIntOrFpInductionRecipe>(&R)) {
-        Phi = cast<PHINode>(State->get(R.getVPSingleValue()));
-      } else {
-        auto *WidenPhi = cast<VPWidenPointerInductionRecipe>(&R);
-        assert(!WidenPhi->onlyScalarsGenerated(State->VF.isScalable()) &&
-               "recipe generating only scalars should have been replaced");
-        auto *GEP = cast<GetElementPtrInst>(State->get(WidenPhi));
-        Phi = cast<PHINode>(GEP->getPointerOperand());
-      }
-
-      Phi->setIncomingBlock(1, VectorLatchBB);
+      // Skip phi-like recipes that generate their backedege values themselves.
+      if (isa<VPWidenPHIRecipe>(&R))
+        continue;
 
-      // Move the last step to the end of the latch block. This ensures
-      // consistent placement of all induction updates.
-      Instruction *Inc = cast<Instruction>(Phi->getIncomingValue(1));
-      Inc->moveBefore(VectorLatchBB->getTerminator()->getPrevNode());
+      if (isa<VPWidenPointerInductionRecipe>(&R) ||
+          isa<VPWidenIntOrFpInductionRecipe>(&R)) {
----------------
alexey-bataev wrote:

```suggestion
      if (isa<VPWidenPointerInductionRecipe,VPWidenIntOrFpInductionRecipe>(&R)) {
```


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