[VPlan] Initial modeling of middle block in VPlan.

[fhahn]

Summary

This patch extends the scope of VPlan to also include the exit (aka
middle) block.

For now, the exit block remains empty, but handling of exit values will
subsequently be moved to VPlan, by adding recipes to model exit values
in the exit block.

As a first step, this will allow fixing #51366.

[Ayal]

Nice preparation for expanding VPlan's scope to include exit/middle-block after its expansion to include preheader.
Looks good to me, adding minor nits.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

3673

Calls for some VPLoopRegion2IRLoop API?

3871

Can getEnclosingLoopRegion() of PhiR's parent? (it can go up to Plan to retrieve/assert it)

8772

nit: "MiddleBlock" >> "MiddleVPBB" (or "ExitVPBB") for consistency?

llvm/lib/Transforms/Vectorize/VPlan.cpp

327

Deserves a comment, potentially starting with "0."

nit: can retain indentation as it should be an "else if"; perhaps better to switch and deal with exit block afterwards (should fail B) for a simpler "else if"("reusing" existing IR Exit Block can then be documented as "D")

[fhahn]

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

3673

Sounds good, there's at least one other potential user. I'll do it as follow-up.

3871

Updated to use getEnclosingLoopRegion, thanks!

8772

Renamed, thanks!

llvm/lib/Transforms/Vectorize/VPlan.cpp

327

Updated to reduce the indent and updated the comment. I added a separate comment for re-using ExitBB, as this is different to re-using the last BB. I also retained the oder of checks as this keeps the existing conditions simpler.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

public:
   /// complex control flow around the loops.
   virtual std::pair<BasicBlock *, Value *> createVectorizedLoopSkeleton();
 
   /// Widen a single call instruction within the innermost loop.
   void widenCallInstruction(CallInst &I, VPValue *Def, VPUser &ArgOperands,
                             VPTransformState &State);
 
   /// Fix the vectorized code, taking care of header phi's, live-outs, and more.
-  void fixVectorizedLoop(VPTransformState &State);
+  void fixVectorizedLoop(VPTransformState &State, VPlan &Plan);
 
   // Return true if any runtime check is added.
   bool areSafetyChecksAdded() { return AddedSafetyChecks; }
 
   /// A type for vectorized values in the new loop. Each value from the
   /// original loop, when vectorized, is represented by UF vector values in the
   /// new unrolled loop, where UF is the unroll factor.
   using VectorParts = SmallVector<Value *, 2>;
for (unsigned Part = 0; Part < UF; ++Part) {
         Value *NewI = Inst->getOperand(0);
         Inst->eraseFromParent();
         State.reset(Def, NewI, Part);
       }
     }
   }
 }
 
-void InnerLoopVectorizer::fixVectorizedLoop(VPTransformState &State) {
+void InnerLoopVectorizer::fixVectorizedLoop(VPTransformState &State,
+                                            VPlan &Plan) {
   // Insert truncates and extends for any truncated instructions as hints to
   // InstCombine.
   if (VF.isVector())
     truncateToMinimalBitwidths(State);
 
   // Fix widened non-induction PHIs by setting up the PHI operands.
   if (OrigPHIsToFix.size()) {
     assert(EnableVPlanNativePath &&
            "Unexpected non-induction PHIs for fixup in non VPlan-native path");
     fixNonInductionPHIs(State);
   }
 
   // At this point every instruction in the original loop is widened to a
   // vector form. Now we need to fix the recurrences in the loop. These PHI
   // nodes are currently empty because we did not want to introduce cycles.
   // This is the second stage of vectorizing recurrences.
   fixCrossIterationPHIs(State);
 
   // Forget the original basic block.
   PSE.getSE()->forgetLoop(OrigLoop);
 
-  Loop *VectorLoop = LI->getLoopFor(State.CFG.PrevBB);
+  VPBasicBlock *LatchVPBB = Plan.getVectorLoopRegion()->getExitBasicBlock();
+  Loop *VectorLoop = LI->getLoopFor(State.CFG.VPBB2IRBB[LatchVPBB]);
   // If we inserted an edge from the middle block to the unique exit block,
   // update uses outside the loop (phis) to account for the newly inserted
   // edge.
   if (!Cost->requiresScalarEpilogue(VF)) {
     // Fix-up external users of the induction variables.
     for (auto &Entry : Legal->getInductionVars())
       fixupIVUsers(Entry.first, Entry.second,
                    getOrCreateVectorTripCount(VectorLoop->getLoopPreheader()),
void InnerLoopVectorizer::fixReduction(VPReductionPHIRecipe *PhiR,
   // the PHIs and the values we are going to write.
   // This allows us to write both PHINodes and the extractelement
   // instructions.
   Builder.SetInsertPoint(&*LoopMiddleBlock->getFirstInsertionPt());
 
   setDebugLocFromInst(LoopExitInst);
 
   Type *PhiTy = OrigPhi->getType();
-  BasicBlock *VectorLoopLatch =
-      LI->getLoopFor(State.CFG.PrevBB)->getLoopLatch();
+
+  VPBasicBlock *LatchVPBB =
+      PhiR->getParent()->getPlan()->getVectorLoopRegion()->getExitBasicBlock();
+  BasicBlock *VectorLoopLatch = State.CFG.VPBB2IRBB[LatchVPBB];
   // If tail is folded by masking, the vector value to leave the loop should be
   // a Select choosing between the vectorized LoopExitInst and vectorized Phi,
   // instead of the former. For an inloop reduction the reduction will already
   // be predicated, and does not need to be handled here.
   if (Cost->foldTailByMasking() && !PhiR->isInLoop()) {
     for (unsigned Part = 0; Part < UF; ++Part) {
       Value *VecLoopExitInst = State.get(LoopExitInstDef, Part);
       Value *Sel = nullptr;
void LoopVectorizationPlanner::executePlan(ElementCount BestVF, unsigned BestUF,
   // Keep all loop hints from the original loop on the vector loop (we'll
   // replace the vectorizer-specific hints below).
   MDNode *OrigLoopID = OrigLoop->getLoopID();
 
   Optional<MDNode *> VectorizedLoopID =
       makeFollowupLoopID(OrigLoopID, {LLVMLoopVectorizeFollowupAll,
                                       LLVMLoopVectorizeFollowupVectorized});
 
-  Loop *L = LI->getLoopFor(State.CFG.PrevBB);
+  VPBasicBlock *HeaderVPBB =
+      BestVPlan.getVectorLoopRegion()->getEntryBasicBlock();
+  Loop *L = LI->getLoopFor(State.CFG.VPBB2IRBB[HeaderVPBB]);
   if (VectorizedLoopID.hasValue())
     L->setLoopID(VectorizedLoopID.getValue());
   else {
     // Keep all loop hints from the original loop on the vector loop (we'll
     // replace the vectorizer-specific hints below).
     if (MDNode *LID = OrigLoop->getLoopID())
       L->setLoopID(LID);
 
     LoopVectorizeHints Hints(L, true, *ORE);
     Hints.setAlreadyVectorized();
   }
   // Disable runtime unrolling when vectorizing the epilogue loop.
   if (CanonicalIVStartValue)
     AddRuntimeUnrollDisableMetaData(L);
 
   // 3. Fix the vectorized code: take care of header phi's, live-outs,
   //    predication, updating analyses.
-  ILV.fixVectorizedLoop(State);
+  ILV.fixVectorizedLoop(State, BestVPlan);
 
   ILV.printDebugTracesAtEnd();
 }
 
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 void LoopVectorizationPlanner::printPlans(raw_ostream &O) {
   for (const auto &Plan : VPlans)
     if (PrintVPlansInDotFormat)
VPlanPtr LoopVectorizationPlanner::buildVPlanWithVPRecipes(
   };
 
   // ---------------------------------------------------------------------------
   // Build initial VPlan: Scan the body of the loop in a topological order to
   // visit each basic block after having visited its predecessor basic blocks.
   // ---------------------------------------------------------------------------
 
   // Create initial VPlan skeleton, starting with a block for the pre-header,
-  // followed by a region for the vector loop. The skeleton vector loop region
-  // contains a header and latch block.
+  // followed by a region for the vector loop, followed by the middle block. The
+  // skeleton vector loop region contains a header and latch block.
   VPBasicBlock *Preheader = new VPBasicBlock("vector.ph");
   auto Plan = std::make_unique<VPlan>(Preheader);
 
   VPBasicBlock *HeaderVPBB = new VPBasicBlock("vector.body");
   VPBasicBlock *LatchVPBB = new VPBasicBlock("vector.latch");
   VPBlockUtils::insertBlockAfter(LatchVPBB, HeaderVPBB);
   auto *TopRegion = new VPRegionBlock(HeaderVPBB, LatchVPBB, "vector loop");
   VPBlockUtils::insertBlockAfter(TopRegion, Preheader);
+  VPBasicBlock *MiddleBlock = new VPBasicBlock("middle.block");
+  VPBlockUtils::insertBlockAfter(MiddleBlock, TopRegion);
 
   Instruction *DLInst =
       getDebugLocFromInstOrOperands(Legal->getPrimaryInduction());
   addCanonicalIVRecipes(*Plan, Legal->getWidestInductionType(),
                         DLInst ? DLInst->getDebugLoc() : DebugLoc(),
                         !CM.foldTailByMasking(), false);
 
   // Scan the body of the loop in a topological order to visit each basic block

llvm/lib/Transforms/Vectorize/VPlan.cpp

void VPBasicBlock::execute(VPTransformState *State) {
   VPBasicBlock *PrevVPBB = State->CFG.PrevVPBB;
   VPBlockBase *SingleHPred = nullptr;
   BasicBlock *NewBB = State->CFG.PrevBB; // Reuse it if possible.
 
   auto IsNonReplicateR = [](VPBlockBase *BB) {
     auto *R = dyn_cast<VPRegionBlock>(BB);
     return R && !R->isReplicator();
   };
 
+  if (getPlan()->getVectorLoopRegion()->getSingleSuccessor() == this) {
+    NewBB = State->CFG.ExitBB;
+    State->CFG.PrevBB = NewBB;
+  } else {
     // 1. Create an IR basic block, or reuse the last one if possible.
     // The last IR basic block is reused, as an optimization, in three cases:
     // A. the first VPBB reuses the loop pre-header BB - when PrevVPBB is null;
     // B. when the current VPBB has a single (hierarchical) predecessor which
     //    is PrevVPBB and the latter has a single (hierarchical) successor which
     //    both are in the same non-replicator region; and
     // C. when the current VPBB is an entry of a region replica - where PrevVPBB
-  //    is the exit of this region from a previous instance, or the predecessor
-  //    of this region.
+    //    is the exit of this region from a previous instance, or the
+    //    predecessor of this region.
     if (PrevVPBB && /* A */
         !((SingleHPred = getSingleHierarchicalPredecessor()) &&
           SingleHPred->getExitBasicBlock() == PrevVPBB &&
           PrevVPBB->getSingleHierarchicalSuccessor() &&
           (SingleHPred->getParent() == getEnclosingLoopRegion() &&
            !IsNonReplicateR(SingleHPred))) &&      /* B */
         !(Replica && getPredecessors().empty())) { /* C */
       NewBB = createEmptyBasicBlock(State->CFG);
       State->Builder.SetInsertPoint(NewBB);
       // Temporarily terminate with unreachable until CFG is rewired.
       UnreachableInst *Terminator = State->Builder.CreateUnreachable();
-    // Register NewBB in its loop. In innermost loops its the same for all BB's.
+      // Register NewBB in its loop. In innermost loops its the same for all
+      // BB's.
       if (State->CurrentVectorLoop)
         State->CurrentVectorLoop->addBasicBlockToLoop(NewBB, *State->LI);
       State->Builder.SetInsertPoint(Terminator);
       State->CFG.PrevBB = NewBB;
     }
+  }
 
   // 2. Fill the IR basic block with IR instructions.
   LLVM_DEBUG(dbgs() << "LV: vectorizing VPBB:" << getName()
                     << " in BB:" << NewBB->getName() << '\n');
 
   State->CFG.VPBB2IRBB[this] = NewBB;
   State->CFG.PrevVPBB = this;
 
for (auto VPBB : State->CFG.VPBBsToFix) {
 
     for (VPBlockBase *SuccVPBlock : VPBB->getHierarchicalSuccessors()) {
       VPBasicBlock *SuccVPBB = SuccVPBlock->getEntryBasicBlock();
       BBTerminator->setSuccessor(Idx, State->CFG.VPBB2IRBB[SuccVPBB]);
       ++Idx;
     }
   }
 
-  BasicBlock *VectorLatchBB = State->CFG.PrevBB;
+  VPBasicBlock *LatchVPBB = getVectorLoopRegion()->getExitBasicBlock();
+  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))
       continue;

llvm/test/Transforms/LoopVectorize/first-order-recurrence-sink-replicate-region.ll

 ; CHECK-NEXT: Successor(s): loop.1.split
 ; CHECK-EMPTY:
 ; CHECK-NEXT: loop.1.split:
 ; CHECK-NEXT:   WIDEN ir<%add> = add ir<%conv>, vp<[[PRED2]]>
 ; CHECK-NEXT:   EMIT vp<[[CAN_IV_NEXT:%.+]]> = VF * UF + vp<[[CAN_IV]]>
 ; CHECK-NEXT:   EMIT branch-on-count vp<[[CAN_IV_NEXT]]> vp<[[VEC_TC]]>
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
+; CHECK-NEXT: Successor(s): middle.block
+; CHECK-EMPTY:
+; CHECK-NEXT: middle.block:
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
 ;
 entry:
   br label %loop
 
 loop:
   %0 = phi i32 [ 0, %entry ], [ %conv, %loop ]

 ; CHECK-NEXT: }
 ; CHECK-NEXT: Successor(s): loop.1
 ; CHECK-EMPTY:
 ; CHECK-NEXT: loop.1:
 ; CHECK-NEXT:   EMIT vp<[[CAN_IV_NEXT:%.+]]> = VF * UF + vp<[[CAN_IV]]>
 ; CHECK-NEXT:   EMIT branch-on-count vp<[[CAN_IV_NEXT]]> vp<[[VEC_TC]]>
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
+; CHECK-NEXT: Successor(s): middle.block
+; CHECK-EMPTY:
+; CHECK-NEXT: middle.block:
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
 ;
 entry:
   br label %loop
 
 loop:
   %recur = phi i32 [ 0, %entry ], [ %recur.next, %loop ]

 ; CHECK-NEXT: loop.0.split:
 ; CHECK-NEXT:   WIDEN ir<%add> = add vp<[[PRED]]>, ir<%recur.next>
 ; CHECK-NEXT:   WIDEN ir<%and.red.next> = and ir<%and.red>, ir<%add>
 ; CHECK-NEXT:   EMIT vp<[[SEL:%.+]]> = select vp<[[MASK]]> ir<%and.red.next> ir<%and.red>
 ; CHECK-NEXT:   EMIT vp<[[CAN_IV_NEXT:%.+]]> = VF * UF + vp<[[CAN_IV]]>
 ; CHECK-NEXT:   EMIT branch-on-count vp<[[CAN_IV_NEXT]]> vp<[[VEC_TC]]>
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
+; CHECK-NEXT: Successor(s): middle.block
+; CHECK-EMPTY:
+; CHECK-NEXT: middle.block:
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
 ;
 entry:
   br label %loop
 
 loop:
   %recur = phi i32 [ 0, %entry ], [ %recur.next, %loop ]

 ; CHECK:      loop.2:
 ; CHECK-NEXT:   WIDEN ir<%add.1> = add ir<%conv>, vp<[[PRED1]]>
 ; CHECK-NEXT:   WIDEN ir<%conv.lv.2> = sext vp<[[PRED2]]>
 ; CHECK-NEXT:   WIDEN ir<%add> = add ir<%add.1>, ir<%conv.lv.2>
 ; CHECK-NEXT:   EMIT vp<[[CAN_IV_NEXT:%.+]]> = VF * UF + vp<[[CAN_IV]]>
 ; CHECK-NEXT:   EMIT branch-on-count vp<[[CAN_IV_NEXT]]> vp<[[VEC_TC]]>
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
+; CHECK-NEXT: Successor(s): middle.block
+; CHECK-EMPTY:
+; CHECK-NEXT: middle.block:
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
 ;
 entry:
   br label %loop
 
 loop:
   %0 = phi i32 [ 0, %entry ], [ %conv, %loop ]

 ; CHECK-NEXT: }
 ; CHECK-NEXT: Successor(s): loop.2
 ; CHECK-EMPTY:
 ; CHECK-NEXT: loop.2:
 ; CHECK-NEXT:   EMIT vp<[[CAN_IV_NEXT:%.+]]> = VF * UF + vp<[[CAN_IV]]>
 ; CHECK-NEXT:   EMIT branch-on-count vp<[[CAN_IV_NEXT]]> vp<[[VEC_TC]]>
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
+; CHECK-NEXT: Successor(s): middle.block
+; CHECK-EMPTY:
+; CHECK-NEXT: middle.block:
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
 ;
 entry:
   br label %loop
 
 loop:                                             ; preds = %loop, %entry
   %recur = phi i32 [ 0, %entry ], [ %recur.next, %loop ]

llvm/test/Transforms/LoopVectorize/vplan-printing.ll

 ; CHECK-NEXT:   WIDEN ir<%lv> = load ir<%arrayidx>
 ; CHECK-NEXT:   WIDEN-CALL ir<%call> = call @llvm.sqrt.f32(ir<%lv>)
 ; CHECK-NEXT:   CLONE ir<%arrayidx2> = getelementptr ir<%x>, vp<[[STEPS]]>
 ; CHECK-NEXT:   WIDEN store ir<%arrayidx2>, ir<%call>
 ; CHECK-NEXT:   EMIT vp<[[CAN_IV_NEXT:%.+]]> = VF * UF +(nuw) vp<[[CAN_IV]]>
 ; CHECK-NEXT:   EMIT branch-on-count vp<[[CAN_IV_NEXT]]> vp<[[VEC_TC]]>
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
+; CHECK-NEXT: Successor(s): middle.block
+; CHECK-EMPTY:
+; CHECK-NEXT: middle.block:
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
 ;
 entry:
   %cmp6 = icmp sgt i64 %n, 0
   br i1 %cmp6, label %for.body, label %for.end
 
 for.body:                                         ; preds = %entry, %for.body

 ; CHECK-NEXT:   WIDEN-SELECT ir<%sel> = select ir<%cmp>, ir<1.000000e+01>, ir<2.000000e+01>
 ; CHECK-NEXT:   WIDEN ir<%add> = fadd ir<%lv>, ir<%sel>
 ; CHECK-NEXT:   CLONE ir<%arrayidx2> = getelementptr ir<%x>, vp<[[STEPS]]>
 ; CHECK-NEXT:   WIDEN store ir<%arrayidx2>, ir<%add>
 ; CHECK-NEXT:   EMIT vp<[[CAN_IV_NEXT:%.+]]> = VF * UF +(nuw) vp<[[CAN_IV]]>
 ; CHECK-NEXT:   EMIT branch-on-count vp<[[CAN_IV_NEXT]]> vp<[[VEC_TC]]>
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
+; CHECK-NEXT: Successor(s): middle.block
+; CHECK-EMPTY:
+; CHECK-NEXT: middle.block:
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
 ;
 entry:
   %cmp6 = icmp sgt i64 %n, 0
   br i1 %cmp6, label %for.body, label %for.end
 
 for.body:                                         ; preds = %entry, %for.body

 ; CHECK-NEXT:   vp<[[STEPS:%.+]]> = SCALAR-STEPS vp<[[CAN_IV]]>, ir<0>, ir<1>
 ; CHECK-NEXT:   CLONE ir<%arrayidx> = getelementptr ir<%y>, vp<[[STEPS]]>
 ; CHECK-NEXT:   WIDEN ir<%lv> = load ir<%arrayidx>
 ; CHECK-NEXT:   REDUCE ir<%red.next> = ir<%red> + fast reduce.fadd (ir<%lv>)
 ; CHECK-NEXT:   EMIT vp<[[CAN_IV_NEXT:%.+]]> = VF * UF +(nuw) vp<[[CAN_IV]]>
 ; CHECK-NEXT:   EMIT branch-on-count vp<[[CAN_IV_NEXT]]> vp<[[VEC_TC]]>
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
+; CHECK-NEXT: Successor(s): middle.block
+; CHECK-EMPTY:
+; CHECK-NEXT: middle.block:
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
 ;
 entry:
   br label %for.body
 
 for.body:                                         ; preds = %entry, %for.body
   %iv = phi i64 [ %iv.next, %for.body ], [ 0, %entry ]

 ; CHECK-NEXT:   EMIT vp<[[NOT:%.+]]> = not ir<%cmp>
 ; CHECK-NEXT:   BLEND %d = ir<0>/vp<[[NOT]]> vp<[[PRED]]>/ir<%cmp>
 ; CHECK-NEXT:   CLONE ir<%idx> = getelementptr ir<%x>, vp<[[STEPS]]>
 ; CHECK-NEXT:   WIDEN store ir<%idx>, ir<%d>
 ; CHECK-NEXT:   EMIT vp<[[CAN_IV_NEXT:%.+]]> = VF * UF +(nuw) vp<[[CAN_IV]]>
 ; CHECK-NEXT:   EMIT branch-on-count vp<[[CAN_IV_NEXT]]> vp<[[VEC_TC]]>
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
+; CHECK-NEXT: Successor(s): middle.block
+; CHECK-EMPTY:
+; CHECK-NEXT: middle.block:
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
 ;
 entry:
   br label %for.body
 
 for.body:                                         ; preds = %for.inc, %entry
   %i = phi i64 [ 0, %entry ], [ %i.next, %for.inc ]

 ; CHECK-NEXT:     store ir<%add> to index 0
 ; CHECK-NEXT:     store ir<1> to index 1
 ; CHECK-NEXT:     store ir<2> to index 2
 ; CHECK-NEXT:     store ir<%AB.3> to index 3
 ; CHECK-NEXT:   EMIT vp<[[CAN_IV_NEXT:%.+]]> = VF * UF +(nuw) vp<[[CAN_IV]]>
 ; CHECK-NEXT:   EMIT branch-on-count vp<[[CAN_IV_NEXT]]> vp<[[VEC_TC]]>
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
+; CHECK-NEXT: Successor(s): middle.block
+; CHECK-EMPTY:
+; CHECK-NEXT: middle.block:
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
 ;
 entry:
   br label %for.body
 
 for.body:
   %iv = phi i64 [ 0, %entry ], [ %iv.next, %for.body ]

 ; CHECK-NEXT:   CLONE ir<%arrayidx2> = getelementptr ir<%b>, vp<[[STEPS]]>
 ; CHECK-NEXT:   WIDEN ir<%l.b> = load ir<%arrayidx2>
 ; CHECK-NEXT:   EMIT vp<[[FMUL:%.+]]> = fmul nnan ninf nsz ir<%l.a> ir<%l.b>
 ; CHECK-NEXT:   REDUCE ir<[[MULADD:%.+]]> = ir<%sum.07> + nnan ninf nsz reduce.fadd (vp<[[FMUL]]>)
 ; CHECK-NEXT:   EMIT vp<[[CAN_IV_NEXT:%.+]]> = VF * UF +(nuw) vp<[[CAN_IV]]>
 ; CHECK-NEXT:   EMIT branch-on-count vp<[[CAN_IV_NEXT]]> vp<[[VEC_TC]]>
 ; CHECK-NEXT:   No successors
 ; CHECK-NEXT: }
+; CHECK-NEXT: Successor(s): middle.block
+; CHECK-EMPTY:
+; CHECK-NEXT: middle.block:
+; CHECK-NEXT: No successors
+; CHECK-NEXT:}
 
 entry:
   br label %for.body
 
 for.body:
   %iv = phi i64 [ 0, %entry ], [ %iv.next, %for.body ]
   %sum.07 = phi float [ 0.000000e+00, %entry ], [ %muladd, %for.body ]
   %arrayidx = getelementptr inbounds float, float* %a, i64 %iv

 ; CHECK-NEXT:    EMIT vp<[[NOT2:%.+]]> = not ir<%cmp2>
 ; CHECK-NEXT:    EMIT vp<[[SEL2:%.+]]> = select vp<[[NOT1]]> vp<[[NOT2]]> ir<false>
 ; CHECK-NEXT:    BLEND %ysd.0 = vp<[[PHI]]>/vp<[[OR1]]> ir<%psd>/vp<[[SEL2]]>
 ; CHECK-NEXT:    WIDEN store ir<%isd>, ir<%ysd.0>
 ; CHECK-NEXT:    EMIT vp<[[CAN_IV_NEXT:%.+]]> = VF * UF +(nuw) vp<[[CAN_IV]]>
 ; CHECK-NEXT:    EMIT branch-on-count vp<[[CAN_IV_NEXT]]> vp<[[VEC_TC]]>
 ; CHECK-NEXT:  No successors
 ; CHECK-NEXT:}
-; CHECK-NEXT:No successors
+; CHECK-NEXT: Successor(s): middle.block
+; CHECK-EMPTY:
+; CHECK-NEXT: middle.block:
+; CHECK-NEXT: No successors
 ; CHECK-NEXT:}
 ;
 entry:
   br label %loop
 
 loop:
   %iv = phi i64 [ 0, %entry ], [ %iv.next, %if.end ]
   %isd = getelementptr inbounds i32, i32* %asd, i64 %iv

 ; CHECK-NEXT:     vp<[[STEPS:%.+]]> = SCALAR-STEPS vp<[[CAN_IV]]>, ir<0>, vp<[[EXP_SCEV]]>
 ; CHECK-NEXT:     WIDEN ir<%v3> = add ir<%v2>, ir<1>
 ; CHECK-NEXT:     REPLICATE ir<%gep> = getelementptr ir<%ptr>, vp<[[STEPS]]>
 ; CHECK-NEXT:     REPLICATE store ir<%v3>, ir<%gep>
 ; CHECK-NEXT:     EMIT vp<[[CAN_INC:%.+]]> = VF * UF +(nuw)  vp<[[CAN_IV]]>
 ; CHECK-NEXT:     EMIT branch-on-count  vp<[[CAN_INC]]> vp<%0>
 ; CHECK-NEXT:   No successors
 ; CHECK-NEXT: }
+; CHECK-NEXT: Successor(s): middle.block
+; CHECK-EMPTY:
+; CHECK-NEXT: middle.block:
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
 ;
 entry:
   %div = udiv i64 %y, 492802768830814060
   %inc = add i64 %div, 1
   br label %loop
 

llvm/test/Transforms/LoopVectorize/vplan-sink-scalars-and-merge-vf1.ll

 ; CHECK:      if.then.0:
 ; CHECK-NEXT: Successor(s): for.inc
 
 ; CHECK:      for.inc:
 ; CHECK-NEXT:  EMIT vp<[[CAN_IV_NEXT:%.+]]> = VF * UF +(nuw) vp<[[CAN_IV]]>
 ; CHECK-NEXT:  EMIT branch-on-count vp<[[CAN_IV_NEXT]]> vp<[[VEC_TC]]>
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
+; CHECK-NEXT: Successor(s): middle.block
+; CHECK-EMPTY:
+; CHECK-NEXT: middle.block:
 ; CHECK-NEXT: No successors
 ; CHECK-NEXT: }
 ;
 entry:
   br label %for.body
 
 for.body:
   %tmp0 = phi i64 [ %tmp6, %for.inc ], [ 0, %entry ]