Revert "[LoopVectorizer] Add support for partial reductions (llvm#92418)"

This reverts commit 060d62b.

It looks like this is triggering an assertion when build llvm-test-suite
on ARM64 macOS.

Reproducer from MultiSource/Benchmarks/Ptrdist/bc/number.c

    target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-n32:64-S128-Fn32"
    target triple = "arm64-apple-macosx15.0.0"

    define void @test(i64 %idx.neg, i8 %0) #0 {
    entry:
      br label %while.body

    while.body:                                       ; preds = %while.body, %entry
      %n1ptr.0.idx131 = phi i64 [ %n1ptr.0.add, %while.body ], [ %idx.neg, %entry ]
      %n2ptr.0.idx130 = phi i64 [ %n2ptr.0.add, %while.body ], [ 0, %entry ]
      %sum.1129 = phi i64 [ %add99, %while.body ], [ 0, %entry ]
      %n1ptr.0.add = add i64 %n1ptr.0.idx131, 1
      %conv = sext i8 %0 to i64
      %n2ptr.0.add = add i64 %n2ptr.0.idx130, 1
      %1 = load i8, ptr null, align 1
      %conv97 = sext i8 %1 to i64
      %mul = mul i64 %conv97, %conv
      %add99 = add i64 %mul, %sum.1129
      %cmp94 = icmp ugt i64 %n1ptr.0.idx131, 0
      %cmp95 = icmp ne i64 %n2ptr.0.idx130, -1
      %2 = and i1 %cmp94, %cmp95
      br i1 %2, label %while.body, label %while.end.loopexit

    while.end.loopexit:                               ; preds = %while.body
      %add99.lcssa = phi i64 [ %add99, %while.body ]
      ret void
    }

    attributes #0 = { "target-cpu"="apple-m1" }

> opt -p loop-vectorize
Assertion failed: ((VF.isScalar() || V->getType()->isVectorTy()) && "scalar values must be stored as (0, 0)"), function set, file VPlan.h, line 284.

Author: fhahn

llvm/include/llvm/Analysis/TargetTransformInfo.h

@@ -211,12 +211,6 @@ typedef TargetTransformInfo TTI;
 /// for IR-level transformations.
 class TargetTransformInfo {
 public:
-  enum PartialReductionExtendKind { PR_None, PR_SignExtend, PR_ZeroExtend };
-
-  /// Get the kind of extension that an instruction represents.
-  static PartialReductionExtendKind
-  getPartialReductionExtendKind(Instruction *I);
-
   /// Construct a TTI object using a type implementing the \c Concept
   /// API below.
   ///
@@ -1286,18 +1280,6 @@ class TargetTransformInfo {
   /// \return if target want to issue a prefetch in address space \p AS.
   bool shouldPrefetchAddressSpace(unsigned AS) const;
 
-  /// \return The cost of a partial reduction, which is a reduction from a
-  /// vector to another vector with fewer elements of larger size. They are
-  /// represented by the llvm.experimental.partial.reduce.add intrinsic, which
-  /// takes an accumulator and a binary operation operand that itself is fed by
-  /// two extends. An example of an operation that uses a partial reduction is a
-  /// dot product, which reduces a vector to another of 4 times fewer elements.
-  InstructionCost
-  getPartialReductionCost(unsigned Opcode, Type *InputType, Type *AccumType,
-                          ElementCount VF, PartialReductionExtendKind OpAExtend,
-                          PartialReductionExtendKind OpBExtend,
-                          std::optional<unsigned> BinOp = std::nullopt) const;
-
   /// \return The maximum interleave factor that any transform should try to
   /// perform for this target. This number depends on the level of parallelism
   /// and the number of execution units in the CPU.
@@ -2125,18 +2107,6 @@ class TargetTransformInfo::Concept {
   /// \return if target want to issue a prefetch in address space \p AS.
   virtual bool shouldPrefetchAddressSpace(unsigned AS) const = 0;
 
-  /// \return The cost of a partial reduction, which is a reduction from a
-  /// vector to another vector with fewer elements of larger size. They are
-  /// represented by the llvm.experimental.partial.reduce.add intrinsic, which
-  /// takes an accumulator and a binary operation operand that itself is fed by
-  /// two extends. An example of an operation that uses a partial reduction is a
-  /// dot product, which reduces a vector to another of 4 times fewer elements.
-  virtual InstructionCost
-  getPartialReductionCost(unsigned Opcode, Type *InputType, Type *AccumType,
-                          ElementCount VF, PartialReductionExtendKind OpAExtend,
-                          PartialReductionExtendKind OpBExtend,
-                          std::optional<unsigned> BinOp) const = 0;
-
   virtual unsigned getMaxInterleaveFactor(ElementCount VF) = 0;
   virtual InstructionCost getArithmeticInstrCost(
       unsigned Opcode, Type *Ty, TTI::TargetCostKind CostKind,
@@ -2816,15 +2786,6 @@ class TargetTransformInfo::Model final : public TargetTransformInfo::Concept {
     return Impl.shouldPrefetchAddressSpace(AS);
   }
 
-  InstructionCost getPartialReductionCost(
-      unsigned Opcode, Type *InputType, Type *AccumType, ElementCount VF,
-      PartialReductionExtendKind OpAExtend,
-      PartialReductionExtendKind OpBExtend,
-      std::optional<unsigned> BinOp = std::nullopt) const override {
-    return Impl.getPartialReductionCost(Opcode, InputType, AccumType, VF,
-                                        OpAExtend, OpBExtend, BinOp);
-  }
-
   unsigned getMaxInterleaveFactor(ElementCount VF) override {
     return Impl.getMaxInterleaveFactor(VF);
   }

llvm/include/llvm/Analysis/TargetTransformInfoImpl.h

@@ -585,15 +585,6 @@ class TargetTransformInfoImplBase {
   bool enableWritePrefetching() const { return false; }
   bool shouldPrefetchAddressSpace(unsigned AS) const { return !AS; }
 
-  InstructionCost
-  getPartialReductionCost(unsigned Opcode, Type *InputType, Type *AccumType,
-                          ElementCount VF,
-                          TTI::PartialReductionExtendKind OpAExtend,
-                          TTI::PartialReductionExtendKind OpBExtend,
-                          std::optional<unsigned> BinOp = std::nullopt) const {
-    return InstructionCost::getInvalid();
-  }
-
   unsigned getMaxInterleaveFactor(ElementCount VF) const { return 1; }
 
   InstructionCost getArithmeticInstrCost(

llvm/lib/Analysis/TargetTransformInfo.cpp

@@ -863,14 +863,6 @@ bool TargetTransformInfo::shouldPrefetchAddressSpace(unsigned AS) const {
   return TTIImpl->shouldPrefetchAddressSpace(AS);
 }
 
-InstructionCost TargetTransformInfo::getPartialReductionCost(
-    unsigned Opcode, Type *InputType, Type *AccumType, ElementCount VF,
-    PartialReductionExtendKind OpAExtend, PartialReductionExtendKind OpBExtend,
-    std::optional<unsigned> BinOp) const {
-  return TTIImpl->getPartialReductionCost(Opcode, InputType, AccumType, VF,
-                                          OpAExtend, OpBExtend, BinOp);
-}
-
 unsigned TargetTransformInfo::getMaxInterleaveFactor(ElementCount VF) const {
   return TTIImpl->getMaxInterleaveFactor(VF);
 }
@@ -982,15 +974,6 @@ InstructionCost TargetTransformInfo::getShuffleCost(
   return Cost;
 }
 
-TargetTransformInfo::PartialReductionExtendKind
-TargetTransformInfo::getPartialReductionExtendKind(Instruction *I) {
-  if (isa<SExtInst>(I))
-    return PR_SignExtend;
-  if (isa<ZExtInst>(I))
-    return PR_ZeroExtend;
-  return PR_None;
-}
-
 TTI::CastContextHint
 TargetTransformInfo::getCastContextHint(const Instruction *I) {
   if (!I)

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.h

@@ -23,7 +23,6 @@
 #include "llvm/CodeGen/BasicTTIImpl.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/Intrinsics.h"
-#include "llvm/Support/InstructionCost.h"
 #include <cstdint>
 #include <optional>
 
@@ -358,61 +357,6 @@ class AArch64TTIImpl : public BasicTTIImplBase<AArch64TTIImpl> {
     return BaseT::isLegalNTLoad(DataType, Alignment);
   }
 
-  InstructionCost
-  getPartialReductionCost(unsigned Opcode, Type *InputType, Type *AccumType,
-                          ElementCount VF,
-                          TTI::PartialReductionExtendKind OpAExtend,
-                          TTI::PartialReductionExtendKind OpBExtend,
-                          std::optional<unsigned> BinOp) const {
-
-    InstructionCost Invalid = InstructionCost::getInvalid();
-    InstructionCost Cost(TTI::TCC_Basic);
-
-    if (Opcode != Instruction::Add)
-      return Invalid;
-
-    EVT InputEVT = EVT::getEVT(InputType);
-    EVT AccumEVT = EVT::getEVT(AccumType);
-
-    if (VF.isScalable() && !ST->isSVEorStreamingSVEAvailable())
-      return Invalid;
-    if (VF.isFixed() && (!ST->isNeonAvailable() || !ST->hasDotProd()))
-      return Invalid;
-
-    if (InputEVT == MVT::i8) {
-      switch (VF.getKnownMinValue()) {
-      default:
-        return Invalid;
-      case 8:
-        if (AccumEVT == MVT::i32)
-          Cost *= 2;
-        else if (AccumEVT != MVT::i64)
-          return Invalid;
-        break;
-      case 16:
-        if (AccumEVT == MVT::i64)
-          Cost *= 2;
-        else if (AccumEVT != MVT::i32)
-          return Invalid;
-        break;
-      }
-    } else if (InputEVT == MVT::i16) {
-      // FIXME: Allow i32 accumulator but increase cost, as we would extend
-      //        it to i64.
-      if (VF.getKnownMinValue() != 8 || AccumEVT != MVT::i64)
-        return Invalid;
-    } else
-      return Invalid;
-
-    if (OpAExtend == TTI::PR_None || OpBExtend == TTI::PR_None)
-      return Invalid;
-
-    if (!BinOp || (*BinOp) != Instruction::Mul)
-      return Invalid;
-
-    return Cost;
-  }
-
   bool enableOrderedReductions() const { return true; }
 
   InstructionCost getInterleavedMemoryOpCost(

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -7605,10 +7605,6 @@ static bool planContainsAdditionalSimplifications(VPlan &Plan,
         }
         continue;
       }
-      // The VPlan-based cost model is more accurate for partial reduction and
-      // comparing against the legacy cost isn't desirable.
-      if (isa<VPPartialReductionRecipe>(&R))
-        return true;
       if (Instruction *UI = GetInstructionForCost(&R))
         SeenInstrs.insert(UI);
     }
@@ -8831,103 +8827,6 @@ VPReplicateRecipe *VPRecipeBuilder::handleReplication(Instruction *I,
   return Recipe;
 }
 
-/// Find all possible partial reductions in the loop and track all of those that
-/// are valid so recipes can be formed later.
-void VPRecipeBuilder::collectScaledReductions(VFRange &Range) {
-  // Find all possible partial reductions.
-  SmallVector<std::pair<PartialReductionChain, unsigned>, 1>
-      PartialReductionChains;
-  for (const auto &[Phi, RdxDesc] : Legal->getReductionVars())
-    if (std::optional<std::pair<PartialReductionChain, unsigned>> Pair =
-            getScaledReduction(Phi, RdxDesc, Range))
-      PartialReductionChains.push_back(*Pair);
-
-  // A partial reduction is invalid if any of its extends are used by
-  // something that isn't another partial reduction. This is because the
-  // extends are intended to be lowered along with the reduction itself.
-
-  // Build up a set of partial reduction bin ops for efficient use checking.
-  SmallSet<User *, 4> PartialReductionBinOps;
-  for (const auto &[PartialRdx, _] : PartialReductionChains)
-    PartialReductionBinOps.insert(PartialRdx.BinOp);
-
-  auto ExtendIsOnlyUsedByPartialReductions =
-      [&PartialReductionBinOps](Instruction *Extend) {
-        return all_of(Extend->users(), [&](const User *U) {
-          return PartialReductionBinOps.contains(U);
-        });
-      };
-
-  // Check if each use of a chain's two extends is a partial reduction
-  // and only add those that don't have non-partial reduction users.
-  for (auto Pair : PartialReductionChains) {
-    PartialReductionChain Chain = Pair.first;
-    if (ExtendIsOnlyUsedByPartialReductions(Chain.ExtendA) &&
-        ExtendIsOnlyUsedByPartialReductions(Chain.ExtendB))
-      ScaledReductionExitInstrs.insert(std::make_pair(Chain.Reduction, Pair));
-  }
-}
-
-std::optional<std::pair<PartialReductionChain, unsigned>>
-VPRecipeBuilder::getScaledReduction(PHINode *PHI,
-                                    const RecurrenceDescriptor &Rdx,
-                                    VFRange &Range) {
-  // TODO: Allow scaling reductions when predicating. The select at
-  // the end of the loop chooses between the phi value and most recent
-  // reduction result, both of which have different VFs to the active lane
-  // mask when scaling.
-  if (CM.blockNeedsPredicationForAnyReason(Rdx.getLoopExitInstr()->getParent()))
-    return std::nullopt;
-
-  auto *Update = dyn_cast<BinaryOperator>(Rdx.getLoopExitInstr());
-  if (!Update)
-    return std::nullopt;
-
-  Value *Op = Update->getOperand(0);
-  if (Op == PHI)
-    Op = Update->getOperand(1);
-
-  auto *BinOp = dyn_cast<BinaryOperator>(Op);
-  if (!BinOp || !BinOp->hasOneUse())
-    return std::nullopt;
-
-  using namespace llvm::PatternMatch;
-  Value *A, *B;
-  if (!match(BinOp->getOperand(0), m_ZExtOrSExt(m_Value(A))) ||
-      !match(BinOp->getOperand(1), m_ZExtOrSExt(m_Value(B))))
-    return std::nullopt;
-
-  Instruction *ExtA = cast<Instruction>(BinOp->getOperand(0));
-  Instruction *ExtB = cast<Instruction>(BinOp->getOperand(1));
-
-  // Check that the extends extend from the same type.
-  if (A->getType() != B->getType())
-    return std::nullopt;
-
-  TTI::PartialReductionExtendKind OpAExtend =
-      TargetTransformInfo::getPartialReductionExtendKind(ExtA);
-  TTI::PartialReductionExtendKind OpBExtend =
-      TargetTransformInfo::getPartialReductionExtendKind(ExtB);
-
-  PartialReductionChain Chain(Rdx.getLoopExitInstr(), ExtA, ExtB, BinOp);
-
-  unsigned TargetScaleFactor =
-      PHI->getType()->getPrimitiveSizeInBits().getKnownScalarFactor(
-          A->getType()->getPrimitiveSizeInBits());
-
-  if (LoopVectorizationPlanner::getDecisionAndClampRange(
-          [&](ElementCount VF) {
-            InstructionCost Cost = TTI->getPartialReductionCost(
-                Update->getOpcode(), A->getType(), PHI->getType(), VF,
-                OpAExtend, OpBExtend, std::make_optional(BinOp->getOpcode()));
-            return Cost.isValid();
-          },
-          Range))
-    return std::make_pair(Chain, TargetScaleFactor);
-
-  return std::nullopt;
-}
-
 VPRecipeBase *
 VPRecipeBuilder::tryToCreateWidenRecipe(Instruction *Instr,
                                         ArrayRef<VPValue *> Operands,
@@ -8952,14 +8851,9 @@ VPRecipeBuilder::tryToCreateWidenRecipe(Instruction *Instr,
           Legal->getReductionVars().find(Phi)->second;
       assert(RdxDesc.getRecurrenceStartValue() ==
              Phi->getIncomingValueForBlock(OrigLoop->getLoopPreheader()));
-
-      // If the PHI is used by a partial reduction, set the scale factor.
-      std::optional<std::pair<PartialReductionChain, unsigned>> Pair =
-          getScaledReductionForInstr(RdxDesc.getLoopExitInstr());
-      unsigned ScaleFactor = Pair ? Pair->second : 1;
-      PhiRecipe = new VPReductionPHIRecipe(
-          Phi, RdxDesc, *StartV, CM.isInLoopReduction(Phi),
-          CM.useOrderedReductions(RdxDesc), ScaleFactor);
+      PhiRecipe = new VPReductionPHIRecipe(Phi, RdxDesc, *StartV,
+                                           CM.isInLoopReduction(Phi),
+                                           CM.useOrderedReductions(RdxDesc));
     } else {
       // TODO: Currently fixed-order recurrences are modeled as chains of
       // first-order recurrences. If there are no users of the intermediate
@@ -8991,9 +8885,6 @@ VPRecipeBuilder::tryToCreateWidenRecipe(Instruction *Instr,
   if (isa<LoadInst>(Instr) || isa<StoreInst>(Instr))
     return tryToWidenMemory(Instr, Operands, Range);
 
-  if (getScaledReductionForInstr(Instr))
-    return tryToCreatePartialReduction(Instr, Operands);
-
   if (!shouldWiden(Instr, Range))
     return nullptr;
 
@@ -9014,21 +8905,6 @@ VPRecipeBuilder::tryToCreateWidenRecipe(Instruction *Instr,
   return tryToWiden(Instr, Operands, VPBB);
 }
 
-VPRecipeBase *
-VPRecipeBuilder::tryToCreatePartialReduction(Instruction *Reduction,
-                                             ArrayRef<VPValue *> Operands) {
-  assert(Operands.size() == 2 &&
-         "Unexpected number of operands for partial reduction");
-
-  VPValue *BinOp = Operands[0];
-  VPValue *Phi = Operands[1];
-  if (isa<VPReductionPHIRecipe>(BinOp->getDefiningRecipe()))
-    std::swap(BinOp, Phi);
-
-  return new VPPartialReductionRecipe(Reduction->getOpcode(), BinOp, Phi,
-                                      Reduction);
-}
-
 void LoopVectorizationPlanner::buildVPlansWithVPRecipes(ElementCount MinVF,
                                                         ElementCount MaxVF) {
   assert(OrigLoop->isInnermost() && "Inner loop expected.");
@@ -9346,8 +9222,7 @@ LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(VFRange &Range) {
   bool HasNUW = !IVUpdateMayOverflow || Style == TailFoldingStyle::None;
   addCanonicalIVRecipes(*Plan, Legal->getWidestInductionType(), HasNUW, DL);
 
-  VPRecipeBuilder RecipeBuilder(*Plan, OrigLoop, TLI, &TTI, Legal, CM, PSE,
-                                Builder);
+  VPRecipeBuilder RecipeBuilder(*Plan, OrigLoop, TLI, Legal, CM, PSE, Builder);
 
   // ---------------------------------------------------------------------------
   // Pre-construction: record ingredients whose recipes we'll need to further
@@ -9393,9 +9268,6 @@ LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(VFRange &Range) {
         bool NeedsBlends = BB != HeaderBB && !BB->phis().empty();
         return Legal->blockNeedsPredication(BB) || NeedsBlends;
       });
-
-  RecipeBuilder.collectScaledReductions(Range);
-
   auto *MiddleVPBB = Plan->getMiddleBlock();
   VPBasicBlock::iterator MBIP = MiddleVPBB->getFirstNonPhi();
   for (BasicBlock *BB : make_range(DFS.beginRPO(), DFS.endRPO())) {