BottomUpVec.cpp

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//===- BottomUpVec.cpp - A bottom-up vectorizer pass ----------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
 
#include "llvm/Transforms/Vectorize/SandboxVectorizer/Passes/BottomUpVec.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/SandboxIR/Function.h"
#include "llvm/SandboxIR/Instruction.h"
#include "llvm/SandboxIR/Module.h"
#include "llvm/SandboxIR/Utils.h"
#include "llvm/Transforms/Vectorize/SandboxVectorizer/SandboxVectorizerPassBuilder.h"
#include "llvm/Transforms/Vectorize/SandboxVectorizer/SeedCollector.h"
#include "llvm/Transforms/Vectorize/SandboxVectorizer/VecUtils.h"
 
namespace llvm {
 
static cl::opt<unsigned>
    OverrideVecRegBits("sbvec-vec-reg-bits", cl::init(0), cl::Hidden,
                       cl::desc("Override the vector register size in bits, "
                                "which is otherwise found by querying TTI."));
static cl::opt<bool>
    AllowNonPow2("sbvec-allow-non-pow2", cl::init(false), cl::Hidden,
                 cl::desc("Allow non-power-of-2 vectorization."));
 
#ifndef NDEBUG
static cl::opt<bool>
    AlwaysVerify("sbvec-always-verify", cl::init(false), cl::Hidden,
                 cl::desc("Helps find bugs by verifying the IR whenever we "
                          "emit new instructions (*very* expensive)."));
#endif // NDEBUG
 
namespace sandboxir {
 
BottomUpVec::BottomUpVec(StringRef Pipeline)
    : FunctionPass("bottom-up-vec"),
      RPM("rpm", Pipeline, SandboxVectorizerPassBuilder::createRegionPass) {}
 
static SmallVector<Value *, 4> getOperand(ArrayRef<Value *> Bndl,
                                          unsigned OpIdx) {
  SmallVector<Value *, 4> Operands;
  for (Value *BndlV : Bndl) {
    auto *BndlI = cast<Instruction>(BndlV);
    Operands.push_back(BndlI->getOperand(OpIdx));
  }
  return Operands;
}
 
/// \Returns the BB iterator after the lowest instruction in \p Vals, or the top
/// of BB if no instruction found in \p Vals.
static BasicBlock::iterator getInsertPointAfterInstrs(ArrayRef<Value *> Vals,
                                                      BasicBlock *BB) {
  auto *BotI = VecUtils::getLastPHIOrSelf(VecUtils::getLowest(Vals, BB));
  if (BotI == nullptr)
    // We are using BB->begin() (or after PHIs) as the fallback insert point.
    return BB->empty()
               ? BB->begin()
               : std::next(
                     VecUtils::getLastPHIOrSelf(&*BB->begin())->getIterator());
  return std::next(BotI->getIterator());
}
 
Value *BottomUpVec::createVectorInstr(ArrayRef<Value *> Bndl,
                                      ArrayRef<Value *> Operands) {
  auto CreateVectorInstr = [](ArrayRef<Value *> Bndl,
                              ArrayRef<Value *> Operands) -> Value * {
    assert(all_of(Bndl, [](auto *V) { return isa<Instruction>(V); }) &&
           "Expect Instructions!");
    auto &Ctx = Bndl[0]->getContext();
 
    Type *ScalarTy = VecUtils::getElementType(Utils::getExpectedType(Bndl[0]));
    auto *VecTy = VecUtils::getWideType(ScalarTy, VecUtils::getNumLanes(Bndl));
 
    BasicBlock::iterator WhereIt = getInsertPointAfterInstrs(
        Bndl, cast<Instruction>(Bndl[0])->getParent());
 
    auto Opcode = cast<Instruction>(Bndl[0])->getOpcode();
    switch (Opcode) {
    case Instruction::Opcode::ZExt:
    case Instruction::Opcode::SExt:
    case Instruction::Opcode::FPToUI:
    case Instruction::Opcode::FPToSI:
    case Instruction::Opcode::FPExt:
    case Instruction::Opcode::PtrToInt:
    case Instruction::Opcode::IntToPtr:
    case Instruction::Opcode::SIToFP:
    case Instruction::Opcode::UIToFP:
    case Instruction::Opcode::Trunc:
    case Instruction::Opcode::FPTrunc:
    case Instruction::Opcode::BitCast: {
      assert(Operands.size() == 1u && "Casts are unary!");
      return CastInst::create(VecTy, Opcode, Operands[0], WhereIt, Ctx,
                              "VCast");
    }
    case Instruction::Opcode::FCmp:
    case Instruction::Opcode::ICmp: {
      auto Pred = cast<CmpInst>(Bndl[0])->getPredicate();
      assert(all_of(drop_begin(Bndl),
                    [Pred](auto *SBV) {
                      return cast<CmpInst>(SBV)->getPredicate() == Pred;
                    }) &&
             "Expected same predicate across bundle.");
      return CmpInst::create(Pred, Operands[0], Operands[1], WhereIt, Ctx,
                             "VCmp");
    }
    case Instruction::Opcode::Select: {
      return SelectInst::create(Operands[0], Operands[1], Operands[2], WhereIt,
                                Ctx, "Vec");
    }
    case Instruction::Opcode::FNeg: {
      auto *UOp0 = cast<UnaryOperator>(Bndl[0]);
      auto OpC = UOp0->getOpcode();
      return UnaryOperator::createWithCopiedFlags(OpC, Operands[0], UOp0,
                                                  WhereIt, Ctx, "Vec");
    }
    case Instruction::Opcode::Add:
    case Instruction::Opcode::FAdd:
    case Instruction::Opcode::Sub:
    case Instruction::Opcode::FSub:
    case Instruction::Opcode::Mul:
    case Instruction::Opcode::FMul:
    case Instruction::Opcode::UDiv:
    case Instruction::Opcode::SDiv:
    case Instruction::Opcode::FDiv:
    case Instruction::Opcode::URem:
    case Instruction::Opcode::SRem:
    case Instruction::Opcode::FRem:
    case Instruction::Opcode::Shl:
    case Instruction::Opcode::LShr:
    case Instruction::Opcode::AShr:
    case Instruction::Opcode::And:
    case Instruction::Opcode::Or:
    case Instruction::Opcode::Xor: {
      auto *BinOp0 = cast<BinaryOperator>(Bndl[0]);
      auto *LHS = Operands[0];
      auto *RHS = Operands[1];
      return BinaryOperator::createWithCopiedFlags(
          BinOp0->getOpcode(), LHS, RHS, BinOp0, WhereIt, Ctx, "Vec");
    }
    case Instruction::Opcode::Load: {
      auto *Ld0 = cast<LoadInst>(Bndl[0]);
      Value *Ptr = Ld0->getPointerOperand();
      return LoadInst::create(VecTy, Ptr, Ld0->getAlign(), WhereIt, Ctx,
                              "VecL");
    }
    case Instruction::Opcode::Store: {
      auto Align = cast<StoreInst>(Bndl[0])->getAlign();
      Value *Val = Operands[0];
      Value *Ptr = Operands[1];
      return StoreInst::create(Val, Ptr, Align, WhereIt, Ctx);
    }
    case Instruction::Opcode::Br:
    case Instruction::Opcode::Ret:
    case Instruction::Opcode::PHI:
    case Instruction::Opcode::AddrSpaceCast:
    case Instruction::Opcode::Call:
    case Instruction::Opcode::GetElementPtr:
      llvm_unreachable("Unimplemented");
      break;
    default:
      llvm_unreachable("Unimplemented");
      break;
    }
    llvm_unreachable("Missing switch case!");
    // TODO: Propagate debug info.
  };
 
  auto *VecI = CreateVectorInstr(Bndl, Operands);
  if (VecI != nullptr) {
    Change = true;
    IMaps->registerVector(Bndl, VecI);
  }
  return VecI;
}
 
void BottomUpVec::tryEraseDeadInstrs() {
  DenseMap<BasicBlock *, SmallVector<Instruction *>> SortedDeadInstrCandidates;
  // The dead instrs could span BBs, so we need to collect and sort them per BB.
  for (auto *DeadI : DeadInstrCandidates)
    SortedDeadInstrCandidates[DeadI->getParent()].push_back(DeadI);
  for (auto &Pair : SortedDeadInstrCandidates)
    sort(Pair.second,
         [](Instruction *I1, Instruction *I2) { return I1->comesBefore(I2); });
  for (const auto &Pair : SortedDeadInstrCandidates) {
    for (Instruction *I : reverse(Pair.second)) {
      if (I->hasNUses(0))
        // Erase the dead instructions bottom-to-top.
        I->eraseFromParent();
    }
  }
  DeadInstrCandidates.clear();
}
 
Value *BottomUpVec::createShuffle(Value *VecOp, const ShuffleMask &Mask,
                                  BasicBlock *UserBB) {
  BasicBlock::iterator WhereIt = getInsertPointAfterInstrs({VecOp}, UserBB);
  return ShuffleVectorInst::create(VecOp, VecOp, Mask, WhereIt,
                                   VecOp->getContext(), "VShuf");
}
 
Value *BottomUpVec::createPack(ArrayRef<Value *> ToPack, BasicBlock *UserBB) {
  BasicBlock::iterator WhereIt = getInsertPointAfterInstrs(ToPack, UserBB);
 
  Type *ScalarTy = VecUtils::getCommonScalarType(ToPack);
  unsigned Lanes = VecUtils::getNumLanes(ToPack);
  Type *VecTy = VecUtils::getWideType(ScalarTy, Lanes);
 
  // Create a series of pack instructions.
  Value *LastInsert = PoisonValue::get(VecTy);
 
  Context &Ctx = ToPack[0]->getContext();
 
  unsigned InsertIdx = 0;
  for (Value *Elm : ToPack) {
    // An element can be either scalar or vector. We need to generate different
    // IR for each case.
    if (Elm->getType()->isVectorTy()) {
      unsigned NumElms =
          cast<FixedVectorType>(Elm->getType())->getNumElements();
      for (auto ExtrLane : seq<int>(0, NumElms)) {
        // We generate extract-insert pairs, for each lane in `Elm`.
        Constant *ExtrLaneC =
            ConstantInt::getSigned(Type::getInt32Ty(Ctx), ExtrLane);
        // This may return a Constant if Elm is a Constant.
        auto *ExtrI =
            ExtractElementInst::create(Elm, ExtrLaneC, WhereIt, Ctx, "VPack");
        if (!isa<Constant>(ExtrI))
          WhereIt = std::next(cast<Instruction>(ExtrI)->getIterator());
        Constant *InsertLaneC =
            ConstantInt::getSigned(Type::getInt32Ty(Ctx), InsertIdx++);
        // This may also return a Constant if ExtrI is a Constant.
        auto *InsertI = InsertElementInst::create(
            LastInsert, ExtrI, InsertLaneC, WhereIt, Ctx, "VPack");
        if (!isa<Constant>(InsertI)) {
          LastInsert = InsertI;
          WhereIt = std::next(cast<Instruction>(LastInsert)->getIterator());
        }
      }
    } else {
      Constant *InsertLaneC =
          ConstantInt::getSigned(Type::getInt32Ty(Ctx), InsertIdx++);
      // This may be folded into a Constant if LastInsert is a Constant. In
      // that case we only collect the last constant.
      LastInsert = InsertElementInst::create(LastInsert, Elm, InsertLaneC,
                                             WhereIt, Ctx, "Pack");
      if (auto *NewI = dyn_cast<Instruction>(LastInsert))
        WhereIt = std::next(NewI->getIterator());
    }
  }
  return LastInsert;
}
 
void BottomUpVec::collectPotentiallyDeadInstrs(ArrayRef<Value *> Bndl) {
  for (Value *V : Bndl)
    DeadInstrCandidates.insert(cast<Instruction>(V));
  // Also collect the GEPs of vectorized loads and stores.
  auto Opcode = cast<Instruction>(Bndl[0])->getOpcode();
  switch (Opcode) {
  case Instruction::Opcode::Load: {
    for (Value *V : drop_begin(Bndl))
      if (auto *Ptr =
              dyn_cast<Instruction>(cast<LoadInst>(V)->getPointerOperand()))
        DeadInstrCandidates.insert(Ptr);
    break;
  }
  case Instruction::Opcode::Store: {
    for (Value *V : drop_begin(Bndl))
      if (auto *Ptr =
              dyn_cast<Instruction>(cast<StoreInst>(V)->getPointerOperand()))
        DeadInstrCandidates.insert(Ptr);
    break;
  }
  default:
    break;
  }
}
 
Value *BottomUpVec::vectorizeRec(ArrayRef<Value *> Bndl,
                                 ArrayRef<Value *> UserBndl, unsigned Depth) {
  Value *NewVec = nullptr;
  auto *UserBB = !UserBndl.empty()
                     ? cast<Instruction>(UserBndl.front())->getParent()
                     : cast<Instruction>(Bndl[0])->getParent();
  const auto &LegalityRes = Legality->canVectorize(Bndl);
  switch (LegalityRes.getSubclassID()) {
  case LegalityResultID::Widen: {
    auto *I = cast<Instruction>(Bndl[0]);
    SmallVector<Value *, 2> VecOperands;
    switch (I->getOpcode()) {
    case Instruction::Opcode::Load:
      // Don't recurse towards the pointer operand.
      VecOperands.push_back(cast<LoadInst>(I)->getPointerOperand());
      break;
    case Instruction::Opcode::Store: {
      // Don't recurse towards the pointer operand.
      auto *VecOp = vectorizeRec(getOperand(Bndl, 0), Bndl, Depth + 1);
      VecOperands.push_back(VecOp);
      VecOperands.push_back(cast<StoreInst>(I)->getPointerOperand());
      break;
    }
    default:
      // Visit all operands.
      for (auto OpIdx : seq<unsigned>(I->getNumOperands())) {
        auto *VecOp = vectorizeRec(getOperand(Bndl, OpIdx), Bndl, Depth + 1);
        VecOperands.push_back(VecOp);
      }
      break;
    }
    NewVec = createVectorInstr(Bndl, VecOperands);
 
    // Collect any potentially dead scalar instructions, including the original
    // scalars and pointer operands of loads/stores.
    if (NewVec != nullptr)
      collectPotentiallyDeadInstrs(Bndl);
    break;
  }
  case LegalityResultID::DiamondReuse: {
    NewVec = cast<DiamondReuse>(LegalityRes).getVector();
    break;
  }
  case LegalityResultID::DiamondReuseWithShuffle: {
    auto *VecOp = cast<DiamondReuseWithShuffle>(LegalityRes).getVector();
    const ShuffleMask &Mask =
        cast<DiamondReuseWithShuffle>(LegalityRes).getMask();
    NewVec = createShuffle(VecOp, Mask, UserBB);
    break;
  }
  case LegalityResultID::DiamondReuseMultiInput: {
    const auto &Descr =
        cast<DiamondReuseMultiInput>(LegalityRes).getCollectDescr();
    Type *ResTy = FixedVectorType::get(Bndl[0]->getType(), Bndl.size());
 
    // TODO: Try to get WhereIt without creating a vector.
    SmallVector<Value *, 4> DescrInstrs;
    for (const auto &ElmDescr : Descr.getDescrs()) {
      if (auto *I = dyn_cast<Instruction>(ElmDescr.getValue()))
        DescrInstrs.push_back(I);
    }
    BasicBlock::iterator WhereIt =
        getInsertPointAfterInstrs(DescrInstrs, UserBB);
 
    Value *LastV = PoisonValue::get(ResTy);
    for (auto [Lane, ElmDescr] : enumerate(Descr.getDescrs())) {
      Value *VecOp = ElmDescr.getValue();
      Context &Ctx = VecOp->getContext();
      Value *ValueToInsert;
      if (ElmDescr.needsExtract()) {
        ConstantInt *IdxC =
            ConstantInt::get(Type::getInt32Ty(Ctx), ElmDescr.getExtractIdx());
        ValueToInsert = ExtractElementInst::create(VecOp, IdxC, WhereIt,
                                                   VecOp->getContext(), "VExt");
      } else {
        ValueToInsert = VecOp;
      }
      ConstantInt *LaneC = ConstantInt::get(Type::getInt32Ty(Ctx), Lane);
      Value *Ins = InsertElementInst::create(LastV, ValueToInsert, LaneC,
                                             WhereIt, Ctx, "VIns");
      LastV = Ins;
    }
    NewVec = LastV;
    break;
  }
  case LegalityResultID::Pack: {
    // If we can't vectorize the seeds then just return.
    if (Depth == 0)
      return nullptr;
    NewVec = createPack(Bndl, UserBB);
    break;
  }
  }
#ifndef NDEBUG
  if (AlwaysVerify) {
    // This helps find broken IR by constantly verifying the function. Note that
    // this is very expensive and should only be used for debugging.
    Instruction *I0 = isa<Instruction>(Bndl[0])
                          ? cast<Instruction>(Bndl[0])
                          : cast<Instruction>(UserBndl[0]);
    assert(!Utils::verifyFunction(I0->getParent()->getParent(), dbgs()) &&
           "Broken function!");
  }
#endif
  return NewVec;
}
 
bool BottomUpVec::tryVectorize(ArrayRef<Value *> Bndl) {
  DeadInstrCandidates.clear();
  Legality->clear();
  vectorizeRec(Bndl, {}, /*Depth=*/0);
  tryEraseDeadInstrs();
  return Change;
}
 
bool BottomUpVec::runOnFunction(Function &F, const Analyses &A) {
  IMaps = std::make_unique<InstrMaps>(F.getContext());
  Legality = std::make_unique<LegalityAnalysis>(
      A.getAA(), A.getScalarEvolution(), F.getParent()->getDataLayout(),
      F.getContext(), *IMaps);
  Change = false;
  const auto &DL = F.getParent()->getDataLayout();
  unsigned VecRegBits =
      OverrideVecRegBits != 0
          ? OverrideVecRegBits
          : A.getTTI()
                .getRegisterBitWidth(TargetTransformInfo::RGK_FixedWidthVector)
                .getFixedValue();
 
  // TODO: Start from innermost BBs first
  for (auto &BB : F) {
    SeedCollector SC(&BB, A.getScalarEvolution());
    for (SeedBundle &Seeds : SC.getStoreSeeds()) {
      unsigned ElmBits =
          Utils::getNumBits(VecUtils::getElementType(Utils::getExpectedType(
                                Seeds[Seeds.getFirstUnusedElementIdx()])),
                            DL);
 
      auto DivideBy2 = [](unsigned Num) {
        auto Floor = VecUtils::getFloorPowerOf2(Num);
        if (Floor == Num)
          return Floor / 2;
        return Floor;
      };
      // Try to create the largest vector supported by the target. If it fails
      // reduce the vector size by half.
      for (unsigned SliceElms = std::min(VecRegBits / ElmBits,
                                         Seeds.getNumUnusedBits() / ElmBits);
           SliceElms >= 2u; SliceElms = DivideBy2(SliceElms)) {
        if (Seeds.allUsed())
          break;
        // Keep trying offsets after FirstUnusedElementIdx, until we vectorize
        // the slice. This could be quite expensive, so we enforce a limit.
        for (unsigned Offset = Seeds.getFirstUnusedElementIdx(),
                      OE = Seeds.size();
             Offset + 1 < OE; Offset += 1) {
          // Seeds are getting used as we vectorize, so skip them.
          if (Seeds.isUsed(Offset))
            continue;
          if (Seeds.allUsed())
            break;
 
          auto SeedSlice =
              Seeds.getSlice(Offset, SliceElms * ElmBits, !AllowNonPow2);
          if (SeedSlice.empty())
            continue;
 
          assert(SeedSlice.size() >= 2 && "Should have been rejected!");
 
          // TODO: If vectorization succeeds, run the RegionPassManager on the
          // resulting region.
 
          // TODO: Refactor to remove the unnecessary copy to SeedSliceVals.
          SmallVector<Value *> SeedSliceVals(SeedSlice.begin(),
                                             SeedSlice.end());
          Change |= tryVectorize(SeedSliceVals);
        }
      }
    }
  }
  return Change;
}
 
} // namespace sandboxir
} // namespace llvm