[VPlan] Use VPInstruction for VPScalarPHIRecipe. (NFCI) (#129767)

Now that all phi nodes manage their incoming blocks through the
VPlan-predecessors, there should be no need for having a dedicate
recipe, it should be sufficient to allow PHI opcodes in VPInstruction.

Follow-ups will also migrate VPWidenPHIRecipe and possibly others,
building on top of #129388.

PR: #129767

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -1005,12 +1005,14 @@ void VPlan::execute(VPTransformState *State) {
       continue;
     }
 
-    auto *PhiR = cast<VPHeaderPHIRecipe>(&R);
-    bool NeedsScalar = isa<VPScalarPHIRecipe>(PhiR) ||
+    auto *PhiR = cast<VPSingleDefRecipe>(&R);
+    // VPInstructions currently model scalar Phis only.
+    bool NeedsScalar = isa<VPInstruction>(PhiR) ||
                        (isa<VPReductionPHIRecipe>(PhiR) &&
                         cast<VPReductionPHIRecipe>(PhiR)->isInLoop());
     Value *Phi = State->get(PhiR, NeedsScalar);
-    Value *Val = State->get(PhiR->getBackedgeValue(), NeedsScalar);
+    // VPHeaderPHIRecipe supports getBackedgeValue() but VPInstruction does not.
+    Value *Val = State->get(PhiR->getOperand(1), NeedsScalar);
     cast<PHINode>(Phi)->addIncoming(Val, VectorLatchBB);
   }
 }

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -441,9 +441,7 @@ class VPRecipeBase : public ilist_node_with_parent<VPRecipeBase, VPBasicBlock>,
   bool mayHaveSideEffects() const;
 
   /// Returns true for PHI-like recipes.
-  bool isPhi() const {
-    return getVPDefID() >= VPFirstPHISC && getVPDefID() <= VPLastPHISC;
-  }
+  bool isPhi() const;
 
   /// Returns true if the recipe may read from memory.
   bool mayReadFromMemory() const;
@@ -1879,45 +1877,6 @@ class VPWidenPointerInductionRecipe : public VPWidenInductionRecipe,
 #endif
 };
 
-/// Recipe to generate a scalar PHI. Used to generate code for recipes that
-/// produce scalar header phis, including VPCanonicalIVPHIRecipe and
-/// VPEVLBasedIVPHIRecipe.
-class VPScalarPHIRecipe : public VPHeaderPHIRecipe {
-  std::string Name;
-
-public:
-  VPScalarPHIRecipe(VPValue *Start, VPValue *BackedgeValue, DebugLoc DL,
-                    StringRef Name)
-      : VPHeaderPHIRecipe(VPDef::VPScalarPHISC, nullptr, Start, DL),
-        Name(Name.str()) {
-    addOperand(BackedgeValue);
-  }
-
-  ~VPScalarPHIRecipe() override = default;
-
-  VPScalarPHIRecipe *clone() override {
-    llvm_unreachable("cloning not implemented yet");
-  }
-
-  VP_CLASSOF_IMPL(VPDef::VPScalarPHISC)
-
-  /// Generate the phi/select nodes.
-  void execute(VPTransformState &State) override;
-
-  /// Returns true if the recipe only uses the first lane of operand \p Op.
-  bool onlyFirstLaneUsed(const VPValue *Op) const override {
-    assert(is_contained(operands(), Op) &&
-           "Op must be an operand of the recipe");
-    return true;
-  }
-
-#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
-  /// Print the recipe.
-  void print(raw_ostream &O, const Twine &Indent,
-             VPSlotTracker &SlotTracker) const override;
-#endif
-};
-
 /// A recipe for widened phis. Incoming values are operands of the recipe and
 /// their operand index corresponds to the incoming predecessor block. If the
 /// recipe is placed in an entry block to a (non-replicate) region, it must have

llvm/lib/Transforms/Vectorize/VPlanAnalysis.cpp

@@ -71,6 +71,10 @@ Type *VPTypeAnalysis::inferScalarTypeForRecipe(const VPInstruction *R) {
   }
   case VPInstruction::ExplicitVectorLength:
     return Type::getIntNTy(Ctx, 32);
+  case Instruction::PHI:
+    // Infer the type of first operand only, as other operands of header phi's
+    // may lead to infinite recursion.
+    return inferScalarType(R->getOperand(0));
   case VPInstruction::FirstOrderRecurrenceSplice:
   case VPInstruction::Not:
   case VPInstruction::ResumePhi:
@@ -236,14 +240,14 @@ Type *VPTypeAnalysis::inferScalarType(const VPValue *V) {
       TypeSwitch<const VPRecipeBase *, Type *>(V->getDefiningRecipe())
           .Case<VPActiveLaneMaskPHIRecipe, VPCanonicalIVPHIRecipe,
                 VPFirstOrderRecurrencePHIRecipe, VPReductionPHIRecipe,
-                VPWidenPointerInductionRecipe, VPEVLBasedIVPHIRecipe,
-                VPScalarPHIRecipe>([this](const auto *R) {
-            // Handle header phi recipes, except VPWidenIntOrFpInduction
-            // which needs special handling due it being possibly truncated.
-            // TODO: consider inferring/caching type of siblings, e.g.,
-            // backedge value, here and in cases below.
-            return inferScalarType(R->getStartValue());
-          })
+                VPWidenPointerInductionRecipe, VPEVLBasedIVPHIRecipe>(
+              [this](const auto *R) {
+                // Handle header phi recipes, except VPWidenIntOrFpInduction
+                // which needs special handling due it being possibly truncated.
+                // TODO: consider inferring/caching type of siblings, e.g.,
+                // backedge value, here and in cases below.
+                return inferScalarType(R->getStartValue());
+              })
           .Case<VPWidenIntOrFpInductionRecipe, VPDerivedIVRecipe>(
               [](const auto *R) { return R->getScalarType(); })
           .Case<VPReductionRecipe, VPPredInstPHIRecipe, VPWidenPHIRecipe,

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -277,6 +277,12 @@ InstructionCost VPRecipeBase::computeCost(ElementCount VF,
   llvm_unreachable("subclasses should implement computeCost");
 }
 
+bool VPRecipeBase::isPhi() const {
+  return (getVPDefID() >= VPFirstPHISC && getVPDefID() <= VPLastPHISC) ||
+         (isa<VPInstruction>(this) &&
+          cast<VPInstruction>(this)->getOpcode() == Instruction::PHI);
+}
+
 InstructionCost
 VPPartialReductionRecipe::computeCost(ElementCount VF,
                                       VPCostContext &Ctx) const {
@@ -418,6 +424,7 @@ bool VPInstruction::canGenerateScalarForFirstLane() const {
     return true;
   switch (Opcode) {
   case Instruction::ICmp:
+  case Instruction::PHI:
   case Instruction::Select:
   case VPInstruction::BranchOnCond:
   case VPInstruction::BranchOnCount:
@@ -467,6 +474,17 @@ Value *VPInstruction::generate(VPTransformState &State) {
     Value *B = State.get(getOperand(1), OnlyFirstLaneUsed);
     return Builder.CreateCmp(getPredicate(), A, B, Name);
   }
+  case Instruction::PHI: {
+    assert(getParent() ==
+               getParent()->getPlan()->getVectorLoopRegion()->getEntry() &&
+           "VPInstructions with PHI opcodes must be used for header phis only "
+           "at the moment");
+    BasicBlock *VectorPH = State.CFG.getPreheaderBBFor(this);
+    Value *Start = State.get(getOperand(0), VPLane(0));
+    PHINode *Phi = State.Builder.CreatePHI(Start->getType(), 2, Name);
+    Phi->addIncoming(Start, VectorPH);
+    return Phi;
+  }
   case Instruction::Select: {
     bool OnlyFirstLaneUsed = vputils::onlyFirstLaneUsed(this);
     Value *Cond = State.get(getOperand(0), OnlyFirstLaneUsed);
@@ -771,7 +789,8 @@ bool VPInstruction::isVectorToScalar() const {
 }
 
 bool VPInstruction::isSingleScalar() const {
-  return getOpcode() == VPInstruction::ResumePhi;
+  return getOpcode() == VPInstruction::ResumePhi ||
+         getOpcode() == Instruction::PHI;
 }
 
 #if !defined(NDEBUG)
@@ -849,6 +868,8 @@ bool VPInstruction::onlyFirstLaneUsed(const VPValue *Op) const {
   switch (getOpcode()) {
   default:
     return false;
+  case Instruction::PHI:
+    return true;
   case Instruction::ICmp:
   case Instruction::Select:
   case Instruction::Or:
@@ -3292,11 +3313,12 @@ void VPWidenPointerInductionRecipe::execute(VPTransformState &State) {
   BasicBlock *VectorPH = State.CFG.getPreheaderBBFor(this);
   PHINode *NewPointerPhi = nullptr;
   if (CurrentPart == 0) {
-    auto *IVR = cast<VPHeaderPHIRecipe>(&getParent()
-                                             ->getPlan()
-                                             ->getVectorLoopRegion()
-                                             ->getEntryBasicBlock()
-                                             ->front());
+    auto *IVR = getParent()
+                    ->getPlan()
+                    ->getVectorLoopRegion()
+                    ->getEntryBasicBlock()
+                    ->front()
+                    .getVPSingleValue();
     PHINode *CanonicalIV = cast<PHINode>(State.get(IVR, /*IsScalar*/ true));
     NewPointerPhi = PHINode::Create(ScStValueType, 2, "pointer.phi",
                                     CanonicalIV->getIterator());
@@ -3665,22 +3687,3 @@ void VPEVLBasedIVPHIRecipe::print(raw_ostream &O, const Twine &Indent,
   printOperands(O, SlotTracker);
 }
 #endif
-
-void VPScalarPHIRecipe::execute(VPTransformState &State) {
-  BasicBlock *VectorPH = State.CFG.getPreheaderBBFor(this);
-  Value *Start = State.get(getStartValue(), VPLane(0));
-  PHINode *Phi = State.Builder.CreatePHI(Start->getType(), 2, Name);
-  Phi->addIncoming(Start, VectorPH);
-  Phi->setDebugLoc(getDebugLoc());
-  State.set(this, Phi, /*IsScalar=*/true);
-}
-
-#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
-void VPScalarPHIRecipe::print(raw_ostream &O, const Twine &Indent,
-                              VPSlotTracker &SlotTracker) const {
-  O << Indent << "SCALAR-PHI ";
-  printAsOperand(O, SlotTracker);
-  O << " = phi ";
-  printOperands(O, SlotTracker);
-}
-#endif

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -1747,7 +1747,7 @@ static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
 
   // Create a scalar phi to track the previous EVL if fixed-order recurrence is
   // contained.
-  VPScalarPHIRecipe *PrevEVL = nullptr;
+  VPInstruction *PrevEVL = nullptr;
   bool ContainsFORs =
       any_of(Header->phis(), IsaPred<VPFirstOrderRecurrencePHIRecipe>);
   if (ContainsFORs) {
@@ -1762,7 +1762,8 @@ static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
           VFSize > 32 ? Instruction::Trunc : Instruction::ZExt, MaxEVL,
           Type::getInt32Ty(Ctx), DebugLoc());
     }
-    PrevEVL = new VPScalarPHIRecipe(MaxEVL, &EVL, DebugLoc(), "prev.evl");
+    PrevEVL = new VPInstruction(Instruction::PHI, {MaxEVL, &EVL}, DebugLoc(),
+                                "prev.evl");
     PrevEVL->insertBefore(*Header, Header->getFirstNonPhi());
   }
 
@@ -2089,9 +2090,9 @@ void VPlanTransforms::convertToConcreteRecipes(VPlan &Plan) {
       auto *PhiR = cast<VPHeaderPHIRecipe>(&R);
       StringRef Name =
           isa<VPCanonicalIVPHIRecipe>(PhiR) ? "index" : "evl.based.iv";
-      auto *ScalarR =
-          new VPScalarPHIRecipe(PhiR->getStartValue(), PhiR->getBackedgeValue(),
-                                PhiR->getDebugLoc(), Name);
+      auto *ScalarR = new VPInstruction(
+          Instruction::PHI, {PhiR->getStartValue(), PhiR->getBackedgeValue()},
+          PhiR->getDebugLoc(), Name);
       ScalarR->insertBefore(PhiR);
       PhiR->replaceAllUsesWith(ScalarR);
       PhiR->eraseFromParent();

llvm/lib/Transforms/Vectorize/VPlanVerifier.cpp

@@ -77,7 +77,9 @@ bool VPlanVerifier::verifyPhiRecipes(const VPBasicBlock *VPBB) {
     if (isa<VPActiveLaneMaskPHIRecipe>(RecipeI))
       NumActiveLaneMaskPhiRecipes++;
 
-    if (IsHeaderVPBB && !isa<VPHeaderPHIRecipe, VPWidenPHIRecipe>(*RecipeI)) {
+    if (IsHeaderVPBB && !isa<VPHeaderPHIRecipe, VPWidenPHIRecipe>(*RecipeI) &&
+        !isa<VPInstruction>(*RecipeI) &&
+        cast<VPInstruction>(RecipeI)->getOpcode() == Instruction::PHI) {
       errs() << "Found non-header PHI recipe in header VPBB";
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
       errs() << ": ";
@@ -143,12 +145,13 @@ bool VPlanVerifier::verifyEVLRecipe(const VPInstruction &EVL) const {
         })
         .Case<VPWidenStoreEVLRecipe, VPReductionEVLRecipe>(
             [&](const VPRecipeBase *S) { return VerifyEVLUse(*S, 2); })
-        .Case<VPWidenLoadEVLRecipe, VPReverseVectorPointerRecipe,
-              VPScalarPHIRecipe>(
+        .Case<VPWidenLoadEVLRecipe, VPReverseVectorPointerRecipe>(
             [&](const VPRecipeBase *R) { return VerifyEVLUse(*R, 1); })
         .Case<VPScalarCastRecipe>(
             [&](const VPScalarCastRecipe *S) { return VerifyEVLUse(*S, 0); })
         .Case<VPInstruction>([&](const VPInstruction *I) {
+          if (I->getOpcode() == Instruction::PHI)
+            return VerifyEVLUse(*I, 1);
           if (I->getOpcode() != Instruction::Add) {
             errs() << "EVL is used as an operand in non-VPInstruction::Add\n";
             return false;
@@ -208,7 +211,9 @@ bool VPlanVerifier::verifyVPBasicBlock(const VPBasicBlock *VPBB) {
         if (!UI ||
             isa<VPHeaderPHIRecipe, VPWidenPHIRecipe, VPPredInstPHIRecipe>(UI) ||
             (isa<VPIRInstruction>(UI) &&
-             isa<PHINode>(cast<VPIRInstruction>(UI)->getInstruction())))
+             isa<PHINode>(cast<VPIRInstruction>(UI)->getInstruction())) ||
+            (isa<VPInstruction>(UI) &&
+             cast<VPInstruction>(UI)->getOpcode() == Instruction::PHI))
           continue;
 
         // If the user is in the same block, check it comes after R in the

llvm/test/Transforms/LoopVectorize/AArch64/vplan-printing.ll

@@ -86,7 +86,7 @@ define i32 @print_partial_reduction(ptr %a, ptr %b) {
 ; CHECK-EMPTY:
 ; CHECK-NEXT: <x1> vector loop: {
 ; CHECK-NEXT:   vector.body:
-; CHECK-NEXT:     SCALAR-PHI vp<[[EP_IV:%.+]]> = phi ir<0>, vp<%index.next>
+; CHECK-NEXT:     EMIT vp<[[EP_IV:%.+]]> = phi ir<0>, vp<%index.next>
 ; CHECK-NEXT:     WIDEN-REDUCTION-PHI ir<%accum> = phi ir<0>, ir<%add> (VF scaled by 1/4)
 ; CHECK-NEXT:     vp<[[STEPS:%.+]]> = SCALAR-STEPS vp<[[EP_IV]]>, ir<1>
 ; CHECK-NEXT:     CLONE ir<%gep.a> = getelementptr ir<%a>, vp<[[STEPS]]>

llvm/test/Transforms/LoopVectorize/RISCV/riscv-vector-reverse.ll

@@ -193,7 +193,7 @@ define void @vector_reverse_i64(ptr nocapture noundef writeonly %A, ptr nocaptur
 ; CHECK-EMPTY:
 ; CHECK-NEXT:  <x1> vector loop: {
 ; CHECK-NEXT:    vector.body:
-; CHECK-NEXT:      SCALAR-PHI vp<[[CAN_IV:%.+]]> = phi ir<0>, vp<[[CAN_IV_NEXT:%.+]]>
+; CHECK-NEXT:      EMIT vp<[[CAN_IV:%.+]]> = phi ir<0>, vp<[[CAN_IV_NEXT:%.+]]>
 ; CHECK-NEXT:      vp<[[DEV_IV:%.+]]> = DERIVED-IV ir<%n> + vp<[[CAN_IV]]> * ir<-1>
 ; CHECK-NEXT:      vp<[[STEPS:%.+]]> = SCALAR-STEPS vp<[[DEV_IV]]>, ir<-1>
 ; CHECK-NEXT:      CLONE ir<%i.0> = add nsw vp<[[STEPS]]>, ir<-1>
@@ -442,7 +442,7 @@ define void @vector_reverse_f32(ptr nocapture noundef writeonly %A, ptr nocaptur
 ; CHECK-EMPTY:
 ; CHECK-NEXT:  <x1> vector loop: {
 ; CHECK-NEXT:    vector.body:
-; CHECK-NEXT:      SCALAR-PHI vp<[[CAN_IV:%.+]]> = phi ir<0>, vp<[[CAN_IV_NEXT:%.+]]>
+; CHECK-NEXT:      EMIT vp<[[CAN_IV:%.+]]> = phi ir<0>, vp<[[CAN_IV_NEXT:%.+]]>
 ; CHECK-NEXT:      vp<[[DEV_IV:%.+]]> = DERIVED-IV ir<%n> + vp<[[CAN_IV]]> * ir<-1>
 ; CHECK-NEXT:      vp<[[STEPS:%.+]]> = SCALAR-STEPS vp<[[DEV_IV]]>, ir<-1>
 ; CHECK-NEXT:      CLONE ir<%i.0> = add nsw vp<[[STEPS]]>, ir<-1>

llvm/test/Transforms/LoopVectorize/RISCV/vplan-vp-intrinsics-fixed-order-recurrence.ll

@@ -27,7 +27,7 @@ define void @first_order_recurrence(ptr noalias %A, ptr noalias %B, i64 %TC) {
 ; IF-EVL-NEXT:     EMIT vp<[[IV:%[0-9]+]]> = CANONICAL-INDUCTION
 ; IF-EVL-NEXT:     EXPLICIT-VECTOR-LENGTH-BASED-IV-PHI vp<[[EVL_PHI:%[0-9]+]]> = phi ir<0>, vp<[[IV_NEXT:%.+]]>
 ; IF-EVL-NEXT:     FIRST-ORDER-RECURRENCE-PHI ir<[[FOR_PHI:%.+]]> = phi ir<33>, ir<[[LD:%.+]]>
-; IF-EVL-NEXT:     SCALAR-PHI vp<[[PREV_EVL:%.+]]> = phi vp<[[VF32]]>, vp<[[EVL:%.+]]>
+; IF-EVL-NEXT:     EMIT vp<[[PREV_EVL:%.+]]> = phi vp<[[VF32]]>, vp<[[EVL:%.+]]>
 ; IF-EVL-NEXT:     EMIT vp<[[AVL:%.+]]> = sub ir<%TC>, vp<[[EVL_PHI]]>
 ; IF-EVL-NEXT:     EMIT vp<[[EVL]]> = EXPLICIT-VECTOR-LENGTH vp<[[AVL]]>
 ; IF-EVL-NEXT:     vp<[[ST:%[0-9]+]]> = SCALAR-STEPS vp<[[EVL_PHI]]>, ir<1>

llvm/test/Transforms/LoopVectorize/RISCV/vplan-vp-select-intrinsics.ll

@@ -32,8 +32,8 @@
 
  ; IF-EVL: <x1> vector loop: {
  ; IF-EVL-NEXT:   vector.body:
- ; IF-EVL-NEXT:     SCALAR-PHI vp<[[IV:%[0-9]+]]> = phi ir<0>, vp<[[IV_NEXT_EXIT:%.+]]>
- ; IF-EVL-NEXT:     SCALAR-PHI vp<[[EVL_PHI:%[0-9]+]]>  = phi ir<0>, vp<[[IV_NEX:%.+]]>
+ ; IF-EVL-NEXT:     EMIT vp<[[IV:%.+]]> = phi ir<0>, vp<[[IV_NEXT_EXIT:%.+]]>
+ ; IF-EVL-NEXT:     EMIT vp<[[EVL_PHI:%.+]]>  = phi ir<0>, vp<[[IV_NEX:%.+]]>
  ; IF-EVL-NEXT:     EMIT vp<[[AVL:%.+]]> = sub ir<%N>, vp<[[EVL_PHI]]>
  ; IF-EVL-NEXT:     EMIT vp<[[EVL:%.+]]> = EXPLICIT-VECTOR-LENGTH vp<[[AVL]]>
  ; IF-EVL-NEXT:     vp<[[ST:%[0-9]+]]> = SCALAR-STEPS vp<[[EVL_PHI]]>, ir<1>