[VPlan] Rename isUniform(AfterVectorization) to isSingleScalar (NFC). (#140134)

Update the naming in VPReplicateRecipe and vputils to the more accurate
isSingleScalar, as the functions check for cases where only a single
scalar is needed, either because it produces the same value for all
lanes or has only their first lane used.

Discussed in #139150.

PR: #140134

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -230,7 +230,7 @@ Value *VPTransformState::get(const VPValue *Def, const VPLane &Lane) {
   if (hasScalarValue(Def, Lane))
     return Data.VPV2Scalars[Def][Lane.mapToCacheIndex(VF)];
 
-  if (!Lane.isFirstLane() && vputils::isUniformAfterVectorization(Def) &&
+  if (!Lane.isFirstLane() && vputils::isSingleScalar(Def) &&
       hasScalarValue(Def, VPLane::getFirstLane())) {
     return Data.VPV2Scalars[Def][0];
   }
@@ -303,17 +303,17 @@ Value *VPTransformState::get(const VPValue *Def, bool NeedsScalar) {
     return ScalarValue;
   }
 
-  bool IsUniform = vputils::isUniformAfterVectorization(Def);
+  bool IsSingleScalar = vputils::isSingleScalar(Def);
 
-  VPLane LastLane(IsUniform ? 0 : VF.getKnownMinValue() - 1);
+  VPLane LastLane(IsSingleScalar ? 0 : VF.getKnownMinValue() - 1);
   // Check if there is a scalar value for the selected lane.
   if (!hasScalarValue(Def, LastLane)) {
     // At the moment, VPWidenIntOrFpInductionRecipes, VPScalarIVStepsRecipes and
-    // VPExpandSCEVRecipes can also be uniform.
+    // VPExpandSCEVRecipes can also be a single scalar.
     assert((isa<VPWidenIntOrFpInductionRecipe, VPScalarIVStepsRecipe,
                 VPExpandSCEVRecipe>(Def->getDefiningRecipe())) &&
            "unexpected recipe found to be invariant");
-    IsUniform = true;
+    IsSingleScalar = true;
     LastLane = 0;
   }
 
@@ -334,7 +334,7 @@ Value *VPTransformState::get(const VPValue *Def, bool NeedsScalar) {
   // resulting vectors are stored in State, we will only generate the
   // insertelements once.
   Value *VectorValue = nullptr;
-  if (IsUniform) {
+  if (IsSingleScalar) {
     VectorValue = GetBroadcastInstrs(ScalarValue);
     set(Def, VectorValue);
   } else {

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -2798,20 +2798,21 @@ class VPMulAccumulateReductionRecipe : public VPReductionRecipe {
 /// VPReplicateRecipe replicates a given instruction producing multiple scalar
 /// copies of the original scalar type, one per lane, instead of producing a
 /// single copy of widened type for all lanes. If the instruction is known to be
-/// uniform only one copy, per lane zero, will be generated.
+/// a single scalar, only one copy, per lane zero, will be generated.
 class VPReplicateRecipe : public VPRecipeWithIRFlags, public VPIRMetadata {
   /// Indicator if only a single replica per lane is needed.
-  bool IsUniform;
+  bool IsSingleScalar;
 
   /// Indicator if the replicas are also predicated.
   bool IsPredicated;
 
 public:
   VPReplicateRecipe(Instruction *I, ArrayRef<VPValue *> Operands,
-                    bool IsUniform, VPValue *Mask = nullptr,
+                    bool IsSingleScalar, VPValue *Mask = nullptr,
                     VPIRMetadata Metadata = {})
       : VPRecipeWithIRFlags(VPDef::VPReplicateSC, Operands, *I),
-        VPIRMetadata(Metadata), IsUniform(IsUniform), IsPredicated(Mask) {
+        VPIRMetadata(Metadata), IsSingleScalar(IsSingleScalar),
+        IsPredicated(Mask) {
     if (Mask)
       addOperand(Mask);
   }
@@ -2820,7 +2821,7 @@ class VPReplicateRecipe : public VPRecipeWithIRFlags, public VPIRMetadata {
 
   VPReplicateRecipe *clone() override {
     auto *Copy =
-        new VPReplicateRecipe(getUnderlyingInstr(), operands(), IsUniform,
+        new VPReplicateRecipe(getUnderlyingInstr(), operands(), IsSingleScalar,
                               isPredicated() ? getMask() : nullptr, *this);
     Copy->transferFlags(*this);
     return Copy;
@@ -2843,15 +2844,15 @@ class VPReplicateRecipe : public VPRecipeWithIRFlags, public VPIRMetadata {
              VPSlotTracker &SlotTracker) const override;
 #endif
 
-  bool isUniform() const { return IsUniform; }
+  bool isSingleScalar() const { return IsSingleScalar; }
 
   bool isPredicated() const { return IsPredicated; }
 
   /// 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 isUniform();
+    return isSingleScalar();
   }
 
   /// Returns true if the recipe uses scalars of operand \p Op.

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -1196,7 +1196,7 @@ void VPIRPhi::execute(VPTransformState &State) {
   PHINode *Phi = &getIRPhi();
   for (const auto &[Idx, Op] : enumerate(operands())) {
     VPValue *ExitValue = Op;
-    auto Lane = vputils::isUniformAfterVectorization(ExitValue)
+    auto Lane = vputils::isSingleScalar(ExitValue)
                     ? VPLane::getFirstLane()
                     : VPLane::getLastLaneForVF(State.VF);
     VPBlockBase *Pred = getParent()->getPredecessors()[Idx];
@@ -2679,7 +2679,7 @@ static void scalarizeInstruction(const Instruction *Instr,
   for (const auto &I : enumerate(RepRecipe->operands())) {
     auto InputLane = Lane;
     VPValue *Operand = I.value();
-    if (vputils::isUniformAfterVectorization(Operand))
+    if (vputils::isSingleScalar(Operand))
       InputLane = VPLane::getFirstLane();
     Cloned->setOperand(I.index(), State.get(Operand, InputLane));
   }
@@ -2705,7 +2705,7 @@ static void scalarizeInstruction(const Instruction *Instr,
 void VPReplicateRecipe::execute(VPTransformState &State) {
   Instruction *UI = getUnderlyingInstr();
   if (State.Lane) { // Generate a single instance.
-    assert((State.VF.isScalar() || !isUniform()) &&
+    assert((State.VF.isScalar() || !isSingleScalar()) &&
            "uniform recipe shouldn't be predicated");
     assert(!State.VF.isScalable() && "Can't scalarize a scalable vector");
     scalarizeInstruction(UI, this, *State.Lane, State);
@@ -2723,16 +2723,15 @@ void VPReplicateRecipe::execute(VPTransformState &State) {
     return;
   }
 
-  if (IsUniform) {
+  if (IsSingleScalar) {
     // Uniform within VL means we need to generate lane 0.
     scalarizeInstruction(UI, this, VPLane(0), State);
     return;
   }
 
   // A store of a loop varying value to a uniform address only needs the last
   // copy of the store.
-  if (isa<StoreInst>(UI) &&
-      vputils::isUniformAfterVectorization(getOperand(1))) {
+  if (isa<StoreInst>(UI) && vputils::isSingleScalar(getOperand(1))) {
     auto Lane = VPLane::getLastLaneForVF(State.VF);
     scalarizeInstruction(UI, this, VPLane(Lane), State);
     return;
@@ -2793,7 +2792,7 @@ InstructionCost VPReplicateRecipe::computeCost(ElementCount VF,
                UI->getOpcode(), ResultTy, CostKind,
                {TargetTransformInfo::OK_AnyValue, TargetTransformInfo::OP_None},
                Op2Info, Operands, UI, &Ctx.TLI) *
-           (isUniform() ? 1 : VF.getKnownMinValue());
+           (isSingleScalar() ? 1 : VF.getKnownMinValue());
   }
   }
 
@@ -2803,7 +2802,7 @@ InstructionCost VPReplicateRecipe::computeCost(ElementCount VF,
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 void VPReplicateRecipe::print(raw_ostream &O, const Twine &Indent,
                               VPSlotTracker &SlotTracker) const {
-  O << Indent << (IsUniform ? "CLONE " : "REPLICATE ");
+  O << Indent << (IsSingleScalar ? "CLONE " : "REPLICATE ");
 
   if (!getUnderlyingInstr()->getType()->isVoidTy()) {
     printAsOperand(O, SlotTracker);

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -151,7 +151,7 @@ static bool sinkScalarOperands(VPlan &Plan) {
         SinkCandidate->mayReadOrWriteMemory())
       continue;
     if (auto *RepR = dyn_cast<VPReplicateRecipe>(SinkCandidate)) {
-      if (!ScalarVFOnly && RepR->isUniform())
+      if (!ScalarVFOnly && RepR->isSingleScalar())
         continue;
     } else if (!isa<VPScalarIVStepsRecipe>(SinkCandidate))
       continue;
@@ -347,7 +347,7 @@ static VPRegionBlock *createReplicateRegion(VPReplicateRecipe *PredRecipe,
   auto *RecipeWithoutMask = new VPReplicateRecipe(
       PredRecipe->getUnderlyingInstr(),
       make_range(PredRecipe->op_begin(), std::prev(PredRecipe->op_end())),
-      PredRecipe->isUniform(), nullptr /*Mask*/, *PredRecipe);
+      PredRecipe->isSingleScalar(), nullptr /*Mask*/, *PredRecipe);
   auto *Pred =
       Plan.createVPBasicBlock(Twine(RegionName) + ".if", RecipeWithoutMask);
 
@@ -643,12 +643,11 @@ static void legalizeAndOptimizeInductions(VPlan &Plan) {
       // Skip recipes that shouldn't be narrowed.
       if (!Def || !isa<VPReplicateRecipe, VPWidenRecipe>(Def) ||
           Def->getNumUsers() == 0 || !Def->getUnderlyingValue() ||
-          (RepR && (RepR->isUniform() || RepR->isPredicated())))
+          (RepR && (RepR->isSingleScalar() || RepR->isPredicated())))
         continue;
 
       // Skip recipes that may have other lanes than their first used.
-      if (!vputils::isUniformAfterVectorization(Def) &&
-          !vputils::onlyFirstLaneUsed(Def))
+      if (!vputils::isSingleScalar(Def) && !vputils::onlyFirstLaneUsed(Def))
         continue;
 
       auto *Clone = new VPReplicateRecipe(Def->getUnderlyingInstr(),

llvm/lib/Transforms/Vectorize/VPlanUtils.cpp

@@ -109,7 +109,7 @@ bool vputils::isUniformAcrossVFsAndUFs(VPValue *V) {
         // VPReplicateRecipe.IsUniform. They are also uniform across UF parts if
         // all their operands are invariant.
         // TODO: Further relax the restrictions.
-        return R->isUniform() &&
+        return R->isSingleScalar() &&
                (isa<LoadInst, StoreInst>(R->getUnderlyingValue())) &&
                all_of(R->operands(), isUniformAcrossVFsAndUFs);
       })

llvm/lib/Transforms/Vectorize/VPlanUtils.h

@@ -37,8 +37,9 @@ VPValue *getOrCreateVPValueForSCEVExpr(VPlan &Plan, const SCEV *Expr,
 /// SCEV expression could be constructed.
 const SCEV *getSCEVExprForVPValue(VPValue *V, ScalarEvolution &SE);
 
-/// Returns true if \p VPV is uniform after vectorization.
-inline bool isUniformAfterVectorization(const VPValue *VPV) {
+/// Returns true if \p VPV is a single scalar, either because it produces the
+/// same value for all lanes or only has its first lane used.
+inline bool isSingleScalar(const VPValue *VPV) {
   auto PreservesUniformity = [](unsigned Opcode) -> bool {
     if (Instruction::isBinaryOp(Opcode) || Instruction::isCast(Opcode))
       return true;
@@ -65,21 +66,19 @@ inline bool isUniformAfterVectorization(const VPValue *VPV) {
     // lanes.
     if (RegionOfR && RegionOfR->isReplicator())
       return false;
-    return Rep->isUniform() ||
-           (PreservesUniformity(Rep->getOpcode()) &&
-            all_of(Rep->operands(), isUniformAfterVectorization));
+    return Rep->isSingleScalar() || (PreservesUniformity(Rep->getOpcode()) &&
+                                     all_of(Rep->operands(), isSingleScalar));
   }
   if (isa<VPWidenGEPRecipe, VPDerivedIVRecipe, VPBlendRecipe>(VPV))
-    return all_of(VPV->getDefiningRecipe()->operands(),
-                  isUniformAfterVectorization);
+    return all_of(VPV->getDefiningRecipe()->operands(), isSingleScalar);
   if (auto *WidenR = dyn_cast<VPWidenRecipe>(VPV)) {
     return PreservesUniformity(WidenR->getOpcode()) &&
-           all_of(WidenR->operands(), isUniformAfterVectorization);
+           all_of(WidenR->operands(), isSingleScalar);
   }
   if (auto *VPI = dyn_cast<VPInstruction>(VPV))
     return VPI->isSingleScalar() || VPI->isVectorToScalar() ||
            (PreservesUniformity(VPI->getOpcode()) &&
-            all_of(VPI->operands(), isUniformAfterVectorization));
+            all_of(VPI->operands(), isSingleScalar));
 
   // VPExpandSCEVRecipes must be placed in the entry and are alway uniform.
   return isa<VPExpandSCEVRecipe>(VPV);