[VPlan] Clean up uses/operands on VPBB deletion.

Update the code responsible for deleting VPBBs and recipes to properly
update users and release operands.

This is another preparation for D84680 & following patches towards
enabling modeling def-use chains in VPlan.

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -181,8 +181,15 @@ VPBlockBase *VPBlockBase::getEnclosingBlockWithPredecessors() {
 
 void VPBlockBase::deleteCFG(VPBlockBase *Entry) {
   SmallVector<VPBlockBase *, 8> Blocks;
-  for (VPBlockBase *Block : depth_first(Entry))
+
+  VPValue DummyValue;
+  for (VPBlockBase *Block : depth_first(Entry)) {
+    // Drop all references in VPBasicBlocks and replace all uses with
+    // DummyValue.
+    if (auto *VPBB = dyn_cast<VPBasicBlock>(Block))
+      VPBB->dropAllReferences(&DummyValue);
     Blocks.push_back(Block);
+  }
 
   for (VPBlockBase *Block : Blocks)
     delete Block;
@@ -305,6 +312,17 @@ void VPBasicBlock::execute(VPTransformState *State) {
   LLVM_DEBUG(dbgs() << "LV: filled BB:" << *NewBB);
 }
 
+void VPBasicBlock::dropAllReferences(VPValue *NewValue) {
+  for (VPRecipeBase &R : Recipes) {
+    if (auto *VPV = R.toVPValue())
+      VPV->replaceAllUsesWith(NewValue);
+
+    if (auto *User = R.toVPUser())
+      for (unsigned I = 0, E = User->getNumOperands(); I != E; I++)
+        User->setOperand(I, NewValue);
+  }
+}
+
 void VPRegionBlock::execute(VPTransformState *State) {
   ReversePostOrderTraversal<VPBlockBase *> RPOT(Entry);
 
@@ -376,6 +394,12 @@ void VPRecipeBase::removeFromParent() {
   Parent = nullptr;
 }
 
+VPValue *VPRecipeBase::toVPValue() {
+  if (auto *V = dyn_cast<VPInstruction>(this))
+    return V;
+  return nullptr;
+}
+
 iplist<VPRecipeBase>::iterator VPRecipeBase::eraseFromParent() {
   assert(getParent() && "Recipe not in any VPBasicBlock");
   return getParent()->getRecipeList().erase(getIterator());

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -680,6 +680,10 @@ public:
   /// Returns a pointer to a VPUser, if the recipe inherits from VPUser or
   /// nullptr otherwise.
   VPUser *toVPUser();
+
+  /// Returns a pointer to a VPValue, if the recipe inherits from VPValue or
+  /// nullptr otherwise.
+  VPValue *toVPValue();
 };
 
 inline bool VPUser::classof(const VPRecipeBase *Recipe) {
@@ -1362,6 +1366,10 @@ public:
   /// this VPBasicBlock, thereby "executing" the VPlan.
   void execute(struct VPTransformState *State) override;
 
+  /// Replace all operands of VPUsers in the block with \p NewValue and also
+  /// replaces all uses of VPValues defined in the block with NewValue.
+  void dropAllReferences(VPValue *NewValue);
+
 private:
   /// Create an IR BasicBlock to hold the output instructions generated by this
   /// VPBasicBlock, and return it. Update the CFGState accordingly.
@@ -2006,10 +2014,7 @@ class VPlanSlp {
 public:
   VPlanSlp(VPInterleavedAccessInfo &IAI, VPBasicBlock &BB) : IAI(IAI), BB(BB) {}
 
-  ~VPlanSlp() {
-    for (auto &KV : BundleToCombined)
-      delete KV.second;
-  }
+  ~VPlanSlp() = default;
 
   /// Tries to build an SLP tree rooted at \p Operands and returns a
   /// VPInstruction combining \p Operands, if they can be combined.

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -35,6 +35,7 @@ void VPlanTransforms::VPInstructionsToVPRecipes(
       Plan->addCBV(NCondBit);
     }
   }
+  VPValue DummyValue;
   for (VPBlockBase *Base : RPOT) {
     // Do not widen instructions in pre-header and exit blocks.
     if (Base->getNumPredecessors() == 0 || Base->getNumSuccessors() == 0)
@@ -48,6 +49,7 @@ void VPlanTransforms::VPInstructionsToVPRecipes(
       VPInstruction *VPInst = cast<VPInstruction>(Ingredient);
       Instruction *Inst = cast<Instruction>(VPInst->getUnderlyingValue());
       if (DeadInstructions.count(Inst)) {
+        VPInst->replaceAllUsesWith(&DummyValue);
         Ingredient->eraseFromParent();
         continue;
       }
@@ -77,6 +79,7 @@ void VPlanTransforms::VPInstructionsToVPRecipes(
             new VPWidenRecipe(*Inst, Plan->mapToVPValues(Inst->operands()));
 
       NewRecipe->insertBefore(Ingredient);
+      VPInst->replaceAllUsesWith(&DummyValue);
       Ingredient->eraseFromParent();
     }
   }

llvm/lib/Transforms/Vectorize/VPlanValue.h

@@ -168,6 +168,10 @@ public:
 
   VPUser(const VPUser &) = delete;
   VPUser &operator=(const VPUser &) = delete;
+  virtual ~VPUser() {
+    for (VPValue *Op : operands())
+      Op->removeUser(*this);
+  }
 
   void addOperand(VPValue *Operand) {
     Operands.push_back(Operand);

llvm/unittests/Transforms/Vectorize/VPlanSlpTest.cpp

@@ -116,6 +116,11 @@ TEST_F(VPlanSlpTest, testSlpSimple_2) {
   auto *CombinedLoadB = cast<VPInstruction>(CombinedAdd->getOperand(1));
   EXPECT_EQ(VPInstruction::SLPLoad, CombinedLoadA->getOpcode());
   EXPECT_EQ(VPInstruction::SLPLoad, CombinedLoadB->getOpcode());
+
+  delete CombinedStore;
+  delete CombinedAdd;
+  delete CombinedLoadA;
+  delete CombinedLoadB;
 }
 
 TEST_F(VPlanSlpTest, testSlpSimple_3) {
@@ -190,6 +195,11 @@ TEST_F(VPlanSlpTest, testSlpSimple_3) {
   VPInstruction *GetB = cast<VPInstruction>(&*std::next(Body->begin(), 3));
   EXPECT_EQ(GetA, CombinedLoadA->getOperand(0));
   EXPECT_EQ(GetB, CombinedLoadB->getOperand(0));
+
+  delete CombinedStore;
+  delete CombinedAdd;
+  delete CombinedLoadA;
+  delete CombinedLoadB;
 }
 
 TEST_F(VPlanSlpTest, testSlpReuse_1) {
@@ -249,6 +259,10 @@ TEST_F(VPlanSlpTest, testSlpReuse_1) {
   auto *CombinedLoadA = cast<VPInstruction>(CombinedAdd->getOperand(0));
   EXPECT_EQ(CombinedLoadA, CombinedAdd->getOperand(1));
   EXPECT_EQ(VPInstruction::SLPLoad, CombinedLoadA->getOpcode());
+
+  delete CombinedStore;
+  delete CombinedAdd;
+  delete CombinedLoadA;
 }
 
 TEST_F(VPlanSlpTest, testSlpReuse_2) {
@@ -355,6 +369,15 @@ static void checkReorderExample(VPInstruction *Store1, VPInstruction *Store2,
   VPInstruction *LoadvD1 = cast<VPInstruction>(&*std::next(Body->begin(), 19));
   EXPECT_EQ(LoadvD0->getOperand(0), CombinedLoadD->getOperand(0));
   EXPECT_EQ(LoadvD1->getOperand(0), CombinedLoadD->getOperand(1));
+
+  delete CombinedStore;
+  delete CombinedAdd;
+  delete CombinedMulAB;
+  delete CombinedMulCD;
+  delete CombinedLoadA;
+  delete CombinedLoadB;
+  delete CombinedLoadC;
+  delete CombinedLoadD;
 }
 
 TEST_F(VPlanSlpTest, testSlpReorder_1) {

llvm/unittests/Transforms/Vectorize/VPlanTest.cpp

@@ -179,6 +179,24 @@ TEST(VPInstructionTest, replaceAllUsesWith) {
   delete VPV3;
 }
 
+TEST(VPInstructionTest, releaseOperandsAtDeletion) {
+  VPValue *VPV1 = new VPValue();
+  VPValue *VPV2 = new VPValue();
+  VPInstruction *I1 = new VPInstruction(0, {VPV1, VPV2});
+
+  EXPECT_EQ(1u, VPV1->getNumUsers());
+  EXPECT_EQ(I1, *VPV1->user_begin());
+  EXPECT_EQ(1u, VPV2->getNumUsers());
+  EXPECT_EQ(I1, *VPV2->user_begin());
+
+  delete I1;
+
+  EXPECT_EQ(0u, VPV1->getNumUsers());
+  EXPECT_EQ(0u, VPV2->getNumUsers());
+
+  delete VPV1;
+  delete VPV2;
+}
 TEST(VPBasicBlockTest, getPlan) {
   {
     VPBasicBlock *VPBB1 = new VPBasicBlock();