| //===- ConstantHoisting.cpp - Prepare code for expensive constants --------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass identifies expensive constants to hoist and coalesces them to |
| // better prepare it for SelectionDAG-based code generation. This works around |
| // the limitations of the basic-block-at-a-time approach. |
| // |
| // First it scans all instructions for integer constants and calculates its |
| // cost. If the constant can be folded into the instruction (the cost is |
| // TCC_Free) or the cost is just a simple operation (TCC_BASIC), then we don't |
| // consider it expensive and leave it alone. This is the default behavior and |
| // the default implementation of getIntImmCost will always return TCC_Free. |
| // |
| // If the cost is more than TCC_BASIC, then the integer constant can't be folded |
| // into the instruction and it might be beneficial to hoist the constant. |
| // Similar constants are coalesced to reduce register pressure and |
| // materialization code. |
| // |
| // When a constant is hoisted, it is also hidden behind a bitcast to force it to |
| // be live-out of the basic block. Otherwise the constant would be just |
| // duplicated and each basic block would have its own copy in the SelectionDAG. |
| // The SelectionDAG recognizes such constants as opaque and doesn't perform |
| // certain transformations on them, which would create a new expensive constant. |
| // |
| // This optimization is only applied to integer constants in instructions and |
| // simple (this means not nested) constant cast expressions. For example: |
| // %0 = load i64* inttoptr (i64 big_constant to i64*) |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/ADT/SmallSet.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Analysis/TargetTransformInfo.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/Dominators.h" |
| #include "llvm/IR/IntrinsicInst.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include <tuple> |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "consthoist" |
| |
| STATISTIC(NumConstantsHoisted, "Number of constants hoisted"); |
| STATISTIC(NumConstantsRebased, "Number of constants rebased"); |
| |
| namespace { |
| struct ConstantUser; |
| struct RebasedConstantInfo; |
| |
| typedef SmallVector<ConstantUser, 8> ConstantUseListType; |
| typedef SmallVector<RebasedConstantInfo, 4> RebasedConstantListType; |
| |
| /// \brief Keeps track of the user of a constant and the operand index where the |
| /// constant is used. |
| struct ConstantUser { |
| Instruction *Inst; |
| unsigned OpndIdx; |
| |
| ConstantUser(Instruction *Inst, unsigned Idx) : Inst(Inst), OpndIdx(Idx) { } |
| }; |
| |
| /// \brief Keeps track of a constant candidate and its uses. |
| struct ConstantCandidate { |
| ConstantUseListType Uses; |
| ConstantInt *ConstInt; |
| unsigned CumulativeCost; |
| |
| ConstantCandidate(ConstantInt *ConstInt) |
| : ConstInt(ConstInt), CumulativeCost(0) { } |
| |
| /// \brief Add the user to the use list and update the cost. |
| void addUser(Instruction *Inst, unsigned Idx, unsigned Cost) { |
| CumulativeCost += Cost; |
| Uses.push_back(ConstantUser(Inst, Idx)); |
| } |
| }; |
| |
| /// \brief This represents a constant that has been rebased with respect to a |
| /// base constant. The difference to the base constant is recorded in Offset. |
| struct RebasedConstantInfo { |
| ConstantUseListType Uses; |
| Constant *Offset; |
| |
| RebasedConstantInfo(ConstantUseListType &&Uses, Constant *Offset) |
| : Uses(std::move(Uses)), Offset(Offset) { } |
| }; |
| |
| /// \brief A base constant and all its rebased constants. |
| struct ConstantInfo { |
| ConstantInt *BaseConstant; |
| RebasedConstantListType RebasedConstants; |
| }; |
| |
| /// \brief The constant hoisting pass. |
| class ConstantHoisting : public FunctionPass { |
| typedef DenseMap<ConstantInt *, unsigned> ConstCandMapType; |
| typedef std::vector<ConstantCandidate> ConstCandVecType; |
| |
| const TargetTransformInfo *TTI; |
| DominatorTree *DT; |
| BasicBlock *Entry; |
| |
| /// Keeps track of constant candidates found in the function. |
| ConstCandVecType ConstCandVec; |
| |
| /// Keep track of cast instructions we already cloned. |
| SmallDenseMap<Instruction *, Instruction *> ClonedCastMap; |
| |
| /// These are the final constants we decided to hoist. |
| SmallVector<ConstantInfo, 8> ConstantVec; |
| public: |
| static char ID; // Pass identification, replacement for typeid |
| ConstantHoisting() : FunctionPass(ID), TTI(nullptr), DT(nullptr), |
| Entry(nullptr) { |
| initializeConstantHoistingPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| bool runOnFunction(Function &Fn) override; |
| |
| const char *getPassName() const override { return "Constant Hoisting"; } |
| |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| AU.setPreservesCFG(); |
| AU.addRequired<DominatorTreeWrapperPass>(); |
| AU.addRequired<TargetTransformInfoWrapperPass>(); |
| } |
| |
| private: |
| /// \brief Initialize the pass. |
| void setup(Function &Fn) { |
| DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); |
| TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(Fn); |
| Entry = &Fn.getEntryBlock(); |
| } |
| |
| /// \brief Cleanup. |
| void cleanup() { |
| ConstantVec.clear(); |
| ClonedCastMap.clear(); |
| ConstCandVec.clear(); |
| |
| TTI = nullptr; |
| DT = nullptr; |
| Entry = nullptr; |
| } |
| |
| Instruction *findMatInsertPt(Instruction *Inst, unsigned Idx = ~0U) const; |
| Instruction *findConstantInsertionPoint(const ConstantInfo &ConstInfo) const; |
| void collectConstantCandidates(ConstCandMapType &ConstCandMap, |
| Instruction *Inst, unsigned Idx, |
| ConstantInt *ConstInt); |
| void collectConstantCandidates(ConstCandMapType &ConstCandMap, |
| Instruction *Inst); |
| void collectConstantCandidates(Function &Fn); |
| void findAndMakeBaseConstant(ConstCandVecType::iterator S, |
| ConstCandVecType::iterator E); |
| void findBaseConstants(); |
| void emitBaseConstants(Instruction *Base, Constant *Offset, |
| const ConstantUser &ConstUser); |
| bool emitBaseConstants(); |
| void deleteDeadCastInst() const; |
| bool optimizeConstants(Function &Fn); |
| }; |
| } |
| |
| char ConstantHoisting::ID = 0; |
| INITIALIZE_PASS_BEGIN(ConstantHoisting, "consthoist", "Constant Hoisting", |
| false, false) |
| INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) |
| INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass) |
| INITIALIZE_PASS_END(ConstantHoisting, "consthoist", "Constant Hoisting", |
| false, false) |
| |
| FunctionPass *llvm::createConstantHoistingPass() { |
| return new ConstantHoisting(); |
| } |
| |
| /// \brief Perform the constant hoisting optimization for the given function. |
| bool ConstantHoisting::runOnFunction(Function &Fn) { |
| if (skipOptnoneFunction(Fn)) |
| return false; |
| |
| DEBUG(dbgs() << "********** Begin Constant Hoisting **********\n"); |
| DEBUG(dbgs() << "********** Function: " << Fn.getName() << '\n'); |
| |
| setup(Fn); |
| |
| bool MadeChange = optimizeConstants(Fn); |
| |
| if (MadeChange) { |
| DEBUG(dbgs() << "********** Function after Constant Hoisting: " |
| << Fn.getName() << '\n'); |
| DEBUG(dbgs() << Fn); |
| } |
| DEBUG(dbgs() << "********** End Constant Hoisting **********\n"); |
| |
| cleanup(); |
| |
| return MadeChange; |
| } |
| |
| |
| /// \brief Find the constant materialization insertion point. |
| Instruction *ConstantHoisting::findMatInsertPt(Instruction *Inst, |
| unsigned Idx) const { |
| // If the operand is a cast instruction, then we have to materialize the |
| // constant before the cast instruction. |
| if (Idx != ~0U) { |
| Value *Opnd = Inst->getOperand(Idx); |
| if (auto CastInst = dyn_cast<Instruction>(Opnd)) |
| if (CastInst->isCast()) |
| return CastInst; |
| } |
| |
| // The simple and common case. This also includes constant expressions. |
| if (!isa<PHINode>(Inst) && !Inst->isEHPad()) |
| return Inst; |
| |
| // We can't insert directly before a phi node or an eh pad. Insert before |
| // the terminator of the incoming or dominating block. |
| assert(Entry != Inst->getParent() && "PHI or landing pad in entry block!"); |
| if (Idx != ~0U && isa<PHINode>(Inst)) |
| return cast<PHINode>(Inst)->getIncomingBlock(Idx)->getTerminator(); |
| |
| BasicBlock *IDom = DT->getNode(Inst->getParent())->getIDom()->getBlock(); |
| return IDom->getTerminator(); |
| } |
| |
| /// \brief Find an insertion point that dominates all uses. |
| Instruction *ConstantHoisting:: |
| findConstantInsertionPoint(const ConstantInfo &ConstInfo) const { |
| assert(!ConstInfo.RebasedConstants.empty() && "Invalid constant info entry."); |
| // Collect all basic blocks. |
| SmallPtrSet<BasicBlock *, 8> BBs; |
| for (auto const &RCI : ConstInfo.RebasedConstants) |
| for (auto const &U : RCI.Uses) |
| BBs.insert(findMatInsertPt(U.Inst, U.OpndIdx)->getParent()); |
| |
| if (BBs.count(Entry)) |
| return &Entry->front(); |
| |
| while (BBs.size() >= 2) { |
| BasicBlock *BB, *BB1, *BB2; |
| BB1 = *BBs.begin(); |
| BB2 = *std::next(BBs.begin()); |
| BB = DT->findNearestCommonDominator(BB1, BB2); |
| if (BB == Entry) |
| return &Entry->front(); |
| BBs.erase(BB1); |
| BBs.erase(BB2); |
| BBs.insert(BB); |
| } |
| assert((BBs.size() == 1) && "Expected only one element."); |
| Instruction &FirstInst = (*BBs.begin())->front(); |
| return findMatInsertPt(&FirstInst); |
| } |
| |
| |
| /// \brief Record constant integer ConstInt for instruction Inst at operand |
| /// index Idx. |
| /// |
| /// The operand at index Idx is not necessarily the constant integer itself. It |
| /// could also be a cast instruction or a constant expression that uses the |
| // constant integer. |
| void ConstantHoisting::collectConstantCandidates(ConstCandMapType &ConstCandMap, |
| Instruction *Inst, |
| unsigned Idx, |
| ConstantInt *ConstInt) { |
| unsigned Cost; |
| // Ask the target about the cost of materializing the constant for the given |
| // instruction and operand index. |
| if (auto IntrInst = dyn_cast<IntrinsicInst>(Inst)) |
| Cost = TTI->getIntImmCost(IntrInst->getIntrinsicID(), Idx, |
| ConstInt->getValue(), ConstInt->getType()); |
| else |
| Cost = TTI->getIntImmCost(Inst->getOpcode(), Idx, ConstInt->getValue(), |
| ConstInt->getType()); |
| |
| // Ignore cheap integer constants. |
| if (Cost > TargetTransformInfo::TCC_Basic) { |
| ConstCandMapType::iterator Itr; |
| bool Inserted; |
| std::tie(Itr, Inserted) = ConstCandMap.insert(std::make_pair(ConstInt, 0)); |
| if (Inserted) { |
| ConstCandVec.push_back(ConstantCandidate(ConstInt)); |
| Itr->second = ConstCandVec.size() - 1; |
| } |
| ConstCandVec[Itr->second].addUser(Inst, Idx, Cost); |
| DEBUG(if (isa<ConstantInt>(Inst->getOperand(Idx))) |
| dbgs() << "Collect constant " << *ConstInt << " from " << *Inst |
| << " with cost " << Cost << '\n'; |
| else |
| dbgs() << "Collect constant " << *ConstInt << " indirectly from " |
| << *Inst << " via " << *Inst->getOperand(Idx) << " with cost " |
| << Cost << '\n'; |
| ); |
| } |
| } |
| |
| /// \brief Scan the instruction for expensive integer constants and record them |
| /// in the constant candidate vector. |
| void ConstantHoisting::collectConstantCandidates(ConstCandMapType &ConstCandMap, |
| Instruction *Inst) { |
| // Skip all cast instructions. They are visited indirectly later on. |
| if (Inst->isCast()) |
| return; |
| |
| // Can't handle inline asm. Skip it. |
| if (auto Call = dyn_cast<CallInst>(Inst)) |
| if (isa<InlineAsm>(Call->getCalledValue())) |
| return; |
| |
| // Scan all operands. |
| for (unsigned Idx = 0, E = Inst->getNumOperands(); Idx != E; ++Idx) { |
| Value *Opnd = Inst->getOperand(Idx); |
| |
| // Visit constant integers. |
| if (auto ConstInt = dyn_cast<ConstantInt>(Opnd)) { |
| collectConstantCandidates(ConstCandMap, Inst, Idx, ConstInt); |
| continue; |
| } |
| |
| // Visit cast instructions that have constant integers. |
| if (auto CastInst = dyn_cast<Instruction>(Opnd)) { |
| // Only visit cast instructions, which have been skipped. All other |
| // instructions should have already been visited. |
| if (!CastInst->isCast()) |
| continue; |
| |
| if (auto *ConstInt = dyn_cast<ConstantInt>(CastInst->getOperand(0))) { |
| // Pretend the constant is directly used by the instruction and ignore |
| // the cast instruction. |
| collectConstantCandidates(ConstCandMap, Inst, Idx, ConstInt); |
| continue; |
| } |
| } |
| |
| // Visit constant expressions that have constant integers. |
| if (auto ConstExpr = dyn_cast<ConstantExpr>(Opnd)) { |
| // Only visit constant cast expressions. |
| if (!ConstExpr->isCast()) |
| continue; |
| |
| if (auto ConstInt = dyn_cast<ConstantInt>(ConstExpr->getOperand(0))) { |
| // Pretend the constant is directly used by the instruction and ignore |
| // the constant expression. |
| collectConstantCandidates(ConstCandMap, Inst, Idx, ConstInt); |
| continue; |
| } |
| } |
| } // end of for all operands |
| } |
| |
| /// \brief Collect all integer constants in the function that cannot be folded |
| /// into an instruction itself. |
| void ConstantHoisting::collectConstantCandidates(Function &Fn) { |
| ConstCandMapType ConstCandMap; |
| for (BasicBlock &BB : Fn) |
| for (Instruction &Inst : BB) |
| collectConstantCandidates(ConstCandMap, &Inst); |
| } |
| |
| /// \brief Find the base constant within the given range and rebase all other |
| /// constants with respect to the base constant. |
| void ConstantHoisting::findAndMakeBaseConstant(ConstCandVecType::iterator S, |
| ConstCandVecType::iterator E) { |
| auto MaxCostItr = S; |
| unsigned NumUses = 0; |
| // Use the constant that has the maximum cost as base constant. |
| for (auto ConstCand = S; ConstCand != E; ++ConstCand) { |
| NumUses += ConstCand->Uses.size(); |
| if (ConstCand->CumulativeCost > MaxCostItr->CumulativeCost) |
| MaxCostItr = ConstCand; |
| } |
| |
| // Don't hoist constants that have only one use. |
| if (NumUses <= 1) |
| return; |
| |
| ConstantInfo ConstInfo; |
| ConstInfo.BaseConstant = MaxCostItr->ConstInt; |
| Type *Ty = ConstInfo.BaseConstant->getType(); |
| |
| // Rebase the constants with respect to the base constant. |
| for (auto ConstCand = S; ConstCand != E; ++ConstCand) { |
| APInt Diff = ConstCand->ConstInt->getValue() - |
| ConstInfo.BaseConstant->getValue(); |
| Constant *Offset = Diff == 0 ? nullptr : ConstantInt::get(Ty, Diff); |
| ConstInfo.RebasedConstants.push_back( |
| RebasedConstantInfo(std::move(ConstCand->Uses), Offset)); |
| } |
| ConstantVec.push_back(std::move(ConstInfo)); |
| } |
| |
| /// \brief Finds and combines constant candidates that can be easily |
| /// rematerialized with an add from a common base constant. |
| void ConstantHoisting::findBaseConstants() { |
| // Sort the constants by value and type. This invalidates the mapping! |
| std::sort(ConstCandVec.begin(), ConstCandVec.end(), |
| [](const ConstantCandidate &LHS, const ConstantCandidate &RHS) { |
| if (LHS.ConstInt->getType() != RHS.ConstInt->getType()) |
| return LHS.ConstInt->getType()->getBitWidth() < |
| RHS.ConstInt->getType()->getBitWidth(); |
| return LHS.ConstInt->getValue().ult(RHS.ConstInt->getValue()); |
| }); |
| |
| // Simple linear scan through the sorted constant candidate vector for viable |
| // merge candidates. |
| auto MinValItr = ConstCandVec.begin(); |
| for (auto CC = std::next(ConstCandVec.begin()), E = ConstCandVec.end(); |
| CC != E; ++CC) { |
| if (MinValItr->ConstInt->getType() == CC->ConstInt->getType()) { |
| // Check if the constant is in range of an add with immediate. |
| APInt Diff = CC->ConstInt->getValue() - MinValItr->ConstInt->getValue(); |
| if ((Diff.getBitWidth() <= 64) && |
| TTI->isLegalAddImmediate(Diff.getSExtValue())) |
| continue; |
| } |
| // We either have now a different constant type or the constant is not in |
| // range of an add with immediate anymore. |
| findAndMakeBaseConstant(MinValItr, CC); |
| // Start a new base constant search. |
| MinValItr = CC; |
| } |
| // Finalize the last base constant search. |
| findAndMakeBaseConstant(MinValItr, ConstCandVec.end()); |
| } |
| |
| /// \brief Updates the operand at Idx in instruction Inst with the result of |
| /// instruction Mat. If the instruction is a PHI node then special |
| /// handling for duplicate values form the same incomming basic block is |
| /// required. |
| /// \return The update will always succeed, but the return value indicated if |
| /// Mat was used for the update or not. |
| static bool updateOperand(Instruction *Inst, unsigned Idx, Instruction *Mat) { |
| if (auto PHI = dyn_cast<PHINode>(Inst)) { |
| // Check if any previous operand of the PHI node has the same incoming basic |
| // block. This is a very odd case that happens when the incoming basic block |
| // has a switch statement. In this case use the same value as the previous |
| // operand(s), otherwise we will fail verification due to different values. |
| // The values are actually the same, but the variable names are different |
| // and the verifier doesn't like that. |
| BasicBlock *IncomingBB = PHI->getIncomingBlock(Idx); |
| for (unsigned i = 0; i < Idx; ++i) { |
| if (PHI->getIncomingBlock(i) == IncomingBB) { |
| Value *IncomingVal = PHI->getIncomingValue(i); |
| Inst->setOperand(Idx, IncomingVal); |
| return false; |
| } |
| } |
| } |
| |
| Inst->setOperand(Idx, Mat); |
| return true; |
| } |
| |
| /// \brief Emit materialization code for all rebased constants and update their |
| /// users. |
| void ConstantHoisting::emitBaseConstants(Instruction *Base, Constant *Offset, |
| const ConstantUser &ConstUser) { |
| Instruction *Mat = Base; |
| if (Offset) { |
| Instruction *InsertionPt = findMatInsertPt(ConstUser.Inst, |
| ConstUser.OpndIdx); |
| Mat = BinaryOperator::Create(Instruction::Add, Base, Offset, |
| "const_mat", InsertionPt); |
| |
| DEBUG(dbgs() << "Materialize constant (" << *Base->getOperand(0) |
| << " + " << *Offset << ") in BB " |
| << Mat->getParent()->getName() << '\n' << *Mat << '\n'); |
| Mat->setDebugLoc(ConstUser.Inst->getDebugLoc()); |
| } |
| Value *Opnd = ConstUser.Inst->getOperand(ConstUser.OpndIdx); |
| |
| // Visit constant integer. |
| if (isa<ConstantInt>(Opnd)) { |
| DEBUG(dbgs() << "Update: " << *ConstUser.Inst << '\n'); |
| if (!updateOperand(ConstUser.Inst, ConstUser.OpndIdx, Mat) && Offset) |
| Mat->eraseFromParent(); |
| DEBUG(dbgs() << "To : " << *ConstUser.Inst << '\n'); |
| return; |
| } |
| |
| // Visit cast instruction. |
| if (auto CastInst = dyn_cast<Instruction>(Opnd)) { |
| assert(CastInst->isCast() && "Expected an cast instruction!"); |
| // Check if we already have visited this cast instruction before to avoid |
| // unnecessary cloning. |
| Instruction *&ClonedCastInst = ClonedCastMap[CastInst]; |
| if (!ClonedCastInst) { |
| ClonedCastInst = CastInst->clone(); |
| ClonedCastInst->setOperand(0, Mat); |
| ClonedCastInst->insertAfter(CastInst); |
| // Use the same debug location as the original cast instruction. |
| ClonedCastInst->setDebugLoc(CastInst->getDebugLoc()); |
| DEBUG(dbgs() << "Clone instruction: " << *CastInst << '\n' |
| << "To : " << *ClonedCastInst << '\n'); |
| } |
| |
| DEBUG(dbgs() << "Update: " << *ConstUser.Inst << '\n'); |
| updateOperand(ConstUser.Inst, ConstUser.OpndIdx, ClonedCastInst); |
| DEBUG(dbgs() << "To : " << *ConstUser.Inst << '\n'); |
| return; |
| } |
| |
| // Visit constant expression. |
| if (auto ConstExpr = dyn_cast<ConstantExpr>(Opnd)) { |
| Instruction *ConstExprInst = ConstExpr->getAsInstruction(); |
| ConstExprInst->setOperand(0, Mat); |
| ConstExprInst->insertBefore(findMatInsertPt(ConstUser.Inst, |
| ConstUser.OpndIdx)); |
| |
| // Use the same debug location as the instruction we are about to update. |
| ConstExprInst->setDebugLoc(ConstUser.Inst->getDebugLoc()); |
| |
| DEBUG(dbgs() << "Create instruction: " << *ConstExprInst << '\n' |
| << "From : " << *ConstExpr << '\n'); |
| DEBUG(dbgs() << "Update: " << *ConstUser.Inst << '\n'); |
| if (!updateOperand(ConstUser.Inst, ConstUser.OpndIdx, ConstExprInst)) { |
| ConstExprInst->eraseFromParent(); |
| if (Offset) |
| Mat->eraseFromParent(); |
| } |
| DEBUG(dbgs() << "To : " << *ConstUser.Inst << '\n'); |
| return; |
| } |
| } |
| |
| /// \brief Hoist and hide the base constant behind a bitcast and emit |
| /// materialization code for derived constants. |
| bool ConstantHoisting::emitBaseConstants() { |
| bool MadeChange = false; |
| for (auto const &ConstInfo : ConstantVec) { |
| // Hoist and hide the base constant behind a bitcast. |
| Instruction *IP = findConstantInsertionPoint(ConstInfo); |
| IntegerType *Ty = ConstInfo.BaseConstant->getType(); |
| Instruction *Base = |
| new BitCastInst(ConstInfo.BaseConstant, Ty, "const", IP); |
| DEBUG(dbgs() << "Hoist constant (" << *ConstInfo.BaseConstant << ") to BB " |
| << IP->getParent()->getName() << '\n' << *Base << '\n'); |
| NumConstantsHoisted++; |
| |
| // Emit materialization code for all rebased constants. |
| for (auto const &RCI : ConstInfo.RebasedConstants) { |
| NumConstantsRebased++; |
| for (auto const &U : RCI.Uses) |
| emitBaseConstants(Base, RCI.Offset, U); |
| } |
| |
| // Use the same debug location as the last user of the constant. |
| assert(!Base->use_empty() && "The use list is empty!?"); |
| assert(isa<Instruction>(Base->user_back()) && |
| "All uses should be instructions."); |
| Base->setDebugLoc(cast<Instruction>(Base->user_back())->getDebugLoc()); |
| |
| // Correct for base constant, which we counted above too. |
| NumConstantsRebased--; |
| MadeChange = true; |
| } |
| return MadeChange; |
| } |
| |
| /// \brief Check all cast instructions we made a copy of and remove them if they |
| /// have no more users. |
| void ConstantHoisting::deleteDeadCastInst() const { |
| for (auto const &I : ClonedCastMap) |
| if (I.first->use_empty()) |
| I.first->eraseFromParent(); |
| } |
| |
| /// \brief Optimize expensive integer constants in the given function. |
| bool ConstantHoisting::optimizeConstants(Function &Fn) { |
| // Collect all constant candidates. |
| collectConstantCandidates(Fn); |
| |
| // There are no constant candidates to worry about. |
| if (ConstCandVec.empty()) |
| return false; |
| |
| // Combine constants that can be easily materialized with an add from a common |
| // base constant. |
| findBaseConstants(); |
| |
| // There are no constants to emit. |
| if (ConstantVec.empty()) |
| return false; |
| |
| // Finally hoist the base constant and emit materialization code for dependent |
| // constants. |
| bool MadeChange = emitBaseConstants(); |
| |
| // Cleanup dead instructions. |
| deleteDeadCastInst(); |
| |
| return MadeChange; |
| } |