| //===- Reassociate.cpp - Reassociate binary expressions -------------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass reassociates commutative expressions in an order that is designed |
| // to promote better constant propagation, GCSE, LICM, PRE, etc. |
| // |
| // For example: 4 + (x + 5) -> x + (4 + 5) |
| // |
| // In the implementation of this algorithm, constants are assigned rank = 0, |
| // function arguments are rank = 1, and other values are assigned ranks |
| // corresponding to the reverse post order traversal of current function |
| // (starting at 2), which effectively gives values in deep loops higher rank |
| // than values not in loops. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "reassociate" |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Constants.h" |
| #include "llvm/DerivedTypes.h" |
| #include "llvm/Function.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/IntrinsicInst.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Assembly/Writer.h" |
| #include "llvm/Support/CFG.h" |
| #include "llvm/Support/IRBuilder.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/ValueHandle.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/PostOrderIterator.h" |
| #include "llvm/ADT/SetVector.h" |
| #include "llvm/ADT/SmallMap.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/ADT/Statistic.h" |
| #include <algorithm> |
| using namespace llvm; |
| |
| STATISTIC(NumChanged, "Number of insts reassociated"); |
| STATISTIC(NumAnnihil, "Number of expr tree annihilated"); |
| STATISTIC(NumFactor , "Number of multiplies factored"); |
| |
| namespace { |
| struct ValueEntry { |
| unsigned Rank; |
| Value *Op; |
| ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {} |
| }; |
| inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) { |
| return LHS.Rank > RHS.Rank; // Sort so that highest rank goes to start. |
| } |
| } |
| |
| #ifndef NDEBUG |
| /// PrintOps - Print out the expression identified in the Ops list. |
| /// |
| static void PrintOps(Instruction *I, const SmallVectorImpl<ValueEntry> &Ops) { |
| Module *M = I->getParent()->getParent()->getParent(); |
| dbgs() << Instruction::getOpcodeName(I->getOpcode()) << " " |
| << *Ops[0].Op->getType() << '\t'; |
| for (unsigned i = 0, e = Ops.size(); i != e; ++i) { |
| dbgs() << "[ "; |
| WriteAsOperand(dbgs(), Ops[i].Op, false, M); |
| dbgs() << ", #" << Ops[i].Rank << "] "; |
| } |
| } |
| #endif |
| |
| namespace { |
| /// \brief Utility class representing a base and exponent pair which form one |
| /// factor of some product. |
| struct Factor { |
| Value *Base; |
| unsigned Power; |
| |
| Factor(Value *Base, unsigned Power) : Base(Base), Power(Power) {} |
| |
| /// \brief Sort factors by their Base. |
| struct BaseSorter { |
| bool operator()(const Factor &LHS, const Factor &RHS) { |
| return LHS.Base < RHS.Base; |
| } |
| }; |
| |
| /// \brief Compare factors for equal bases. |
| struct BaseEqual { |
| bool operator()(const Factor &LHS, const Factor &RHS) { |
| return LHS.Base == RHS.Base; |
| } |
| }; |
| |
| /// \brief Sort factors in descending order by their power. |
| struct PowerDescendingSorter { |
| bool operator()(const Factor &LHS, const Factor &RHS) { |
| return LHS.Power > RHS.Power; |
| } |
| }; |
| |
| /// \brief Compare factors for equal powers. |
| struct PowerEqual { |
| bool operator()(const Factor &LHS, const Factor &RHS) { |
| return LHS.Power == RHS.Power; |
| } |
| }; |
| }; |
| } |
| |
| namespace { |
| class Reassociate : public FunctionPass { |
| DenseMap<BasicBlock*, unsigned> RankMap; |
| DenseMap<AssertingVH<Value>, unsigned> ValueRankMap; |
| SetVector<AssertingVH<Instruction> > RedoInsts; |
| bool MadeChange; |
| public: |
| static char ID; // Pass identification, replacement for typeid |
| Reassociate() : FunctionPass(ID) { |
| initializeReassociatePass(*PassRegistry::getPassRegistry()); |
| } |
| |
| bool runOnFunction(Function &F); |
| |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.setPreservesCFG(); |
| } |
| private: |
| void BuildRankMap(Function &F); |
| unsigned getRank(Value *V); |
| Value *ReassociateExpression(BinaryOperator *I); |
| void RewriteExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops); |
| Value *OptimizeExpression(BinaryOperator *I, |
| SmallVectorImpl<ValueEntry> &Ops); |
| Value *OptimizeAdd(Instruction *I, SmallVectorImpl<ValueEntry> &Ops); |
| bool collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops, |
| SmallVectorImpl<Factor> &Factors); |
| Value *buildMinimalMultiplyDAG(IRBuilder<> &Builder, |
| SmallVectorImpl<Factor> &Factors); |
| Value *OptimizeMul(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops); |
| Value *RemoveFactorFromExpression(Value *V, Value *Factor); |
| void EraseInst(Instruction *I); |
| void OptimizeInst(Instruction *I); |
| }; |
| } |
| |
| char Reassociate::ID = 0; |
| INITIALIZE_PASS(Reassociate, "reassociate", |
| "Reassociate expressions", false, false) |
| |
| // Public interface to the Reassociate pass |
| FunctionPass *llvm::createReassociatePass() { return new Reassociate(); } |
| |
| /// isReassociableOp - Return true if V is an instruction of the specified |
| /// opcode and if it only has one use. |
| static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) { |
| if (V->hasOneUse() && isa<Instruction>(V) && |
| cast<Instruction>(V)->getOpcode() == Opcode) |
| return cast<BinaryOperator>(V); |
| return 0; |
| } |
| |
| static bool isUnmovableInstruction(Instruction *I) { |
| if (I->getOpcode() == Instruction::PHI || |
| I->getOpcode() == Instruction::LandingPad || |
| I->getOpcode() == Instruction::Alloca || |
| I->getOpcode() == Instruction::Load || |
| I->getOpcode() == Instruction::Invoke || |
| (I->getOpcode() == Instruction::Call && |
| !isa<DbgInfoIntrinsic>(I)) || |
| I->getOpcode() == Instruction::UDiv || |
| I->getOpcode() == Instruction::SDiv || |
| I->getOpcode() == Instruction::FDiv || |
| I->getOpcode() == Instruction::URem || |
| I->getOpcode() == Instruction::SRem || |
| I->getOpcode() == Instruction::FRem) |
| return true; |
| return false; |
| } |
| |
| void Reassociate::BuildRankMap(Function &F) { |
| unsigned i = 2; |
| |
| // Assign distinct ranks to function arguments |
| for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I) |
| ValueRankMap[&*I] = ++i; |
| |
| ReversePostOrderTraversal<Function*> RPOT(&F); |
| for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(), |
| E = RPOT.end(); I != E; ++I) { |
| BasicBlock *BB = *I; |
| unsigned BBRank = RankMap[BB] = ++i << 16; |
| |
| // Walk the basic block, adding precomputed ranks for any instructions that |
| // we cannot move. This ensures that the ranks for these instructions are |
| // all different in the block. |
| for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) |
| if (isUnmovableInstruction(I)) |
| ValueRankMap[&*I] = ++BBRank; |
| } |
| } |
| |
| unsigned Reassociate::getRank(Value *V) { |
| Instruction *I = dyn_cast<Instruction>(V); |
| if (I == 0) { |
| if (isa<Argument>(V)) return ValueRankMap[V]; // Function argument. |
| return 0; // Otherwise it's a global or constant, rank 0. |
| } |
| |
| if (unsigned Rank = ValueRankMap[I]) |
| return Rank; // Rank already known? |
| |
| // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that |
| // we can reassociate expressions for code motion! Since we do not recurse |
| // for PHI nodes, we cannot have infinite recursion here, because there |
| // cannot be loops in the value graph that do not go through PHI nodes. |
| unsigned Rank = 0, MaxRank = RankMap[I->getParent()]; |
| for (unsigned i = 0, e = I->getNumOperands(); |
| i != e && Rank != MaxRank; ++i) |
| Rank = std::max(Rank, getRank(I->getOperand(i))); |
| |
| // If this is a not or neg instruction, do not count it for rank. This |
| // assures us that X and ~X will have the same rank. |
| if (!I->getType()->isIntegerTy() || |
| (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I))) |
| ++Rank; |
| |
| //DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = " |
| // << Rank << "\n"); |
| |
| return ValueRankMap[I] = Rank; |
| } |
| |
| /// LowerNegateToMultiply - Replace 0-X with X*-1. |
| /// |
| static BinaryOperator *LowerNegateToMultiply(Instruction *Neg) { |
| Constant *Cst = Constant::getAllOnesValue(Neg->getType()); |
| |
| BinaryOperator *Res = |
| BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg); |
| Neg->setOperand(1, Constant::getNullValue(Neg->getType())); // Drop use of op. |
| Res->takeName(Neg); |
| Neg->replaceAllUsesWith(Res); |
| Res->setDebugLoc(Neg->getDebugLoc()); |
| return Res; |
| } |
| |
| /// CarmichaelShift - Returns k such that lambda(2^Bitwidth) = 2^k, where lambda |
| /// is the Carmichael function. This means that x^(2^k) === 1 mod 2^Bitwidth for |
| /// every odd x, i.e. x^(2^k) = 1 for every odd x in Bitwidth-bit arithmetic. |
| /// Note that 0 <= k < Bitwidth, and if Bitwidth > 3 then x^(2^k) = 0 for every |
| /// even x in Bitwidth-bit arithmetic. |
| static unsigned CarmichaelShift(unsigned Bitwidth) { |
| if (Bitwidth < 3) |
| return Bitwidth - 1; |
| return Bitwidth - 2; |
| } |
| |
| /// IncorporateWeight - Add the extra weight 'RHS' to the existing weight 'LHS', |
| /// reducing the combined weight using any special properties of the operation. |
| /// The existing weight LHS represents the computation X op X op ... op X where |
| /// X occurs LHS times. The combined weight represents X op X op ... op X with |
| /// X occurring LHS + RHS times. If op is "Xor" for example then the combined |
| /// operation is equivalent to X if LHS + RHS is odd, or 0 if LHS + RHS is even; |
| /// the routine returns 1 in LHS in the first case, and 0 in LHS in the second. |
| static void IncorporateWeight(APInt &LHS, const APInt &RHS, unsigned Opcode) { |
| // If we were working with infinite precision arithmetic then the combined |
| // weight would be LHS + RHS. But we are using finite precision arithmetic, |
| // and the APInt sum LHS + RHS may not be correct if it wraps (it is correct |
| // for nilpotent operations and addition, but not for idempotent operations |
| // and multiplication), so it is important to correctly reduce the combined |
| // weight back into range if wrapping would be wrong. |
| |
| // If RHS is zero then the weight didn't change. |
| if (RHS.isMinValue()) |
| return; |
| // If LHS is zero then the combined weight is RHS. |
| if (LHS.isMinValue()) { |
| LHS = RHS; |
| return; |
| } |
| // From this point on we know that neither LHS nor RHS is zero. |
| |
| if (Instruction::isIdempotent(Opcode)) { |
| // Idempotent means X op X === X, so any non-zero weight is equivalent to a |
| // weight of 1. Keeping weights at zero or one also means that wrapping is |
| // not a problem. |
| assert(LHS == 1 && RHS == 1 && "Weights not reduced!"); |
| return; // Return a weight of 1. |
| } |
| if (Instruction::isNilpotent(Opcode)) { |
| // Nilpotent means X op X === 0, so reduce weights modulo 2. |
| assert(LHS == 1 && RHS == 1 && "Weights not reduced!"); |
| LHS = 0; // 1 + 1 === 0 modulo 2. |
| return; |
| } |
| if (Opcode == Instruction::Add) { |
| // TODO: Reduce the weight by exploiting nsw/nuw? |
| LHS += RHS; |
| return; |
| } |
| |
| assert(Opcode == Instruction::Mul && "Unknown associative operation!"); |
| unsigned Bitwidth = LHS.getBitWidth(); |
| // If CM is the Carmichael number then a weight W satisfying W >= CM+Bitwidth |
| // can be replaced with W-CM. That's because x^W=x^(W-CM) for every Bitwidth |
| // bit number x, since either x is odd in which case x^CM = 1, or x is even in |
| // which case both x^W and x^(W - CM) are zero. By subtracting off multiples |
| // of CM like this weights can always be reduced to the range [0, CM+Bitwidth) |
| // which by a happy accident means that they can always be represented using |
| // Bitwidth bits. |
| // TODO: Reduce the weight by exploiting nsw/nuw? (Could do much better than |
| // the Carmichael number). |
| if (Bitwidth > 3) { |
| /// CM - The value of Carmichael's lambda function. |
| APInt CM = APInt::getOneBitSet(Bitwidth, CarmichaelShift(Bitwidth)); |
| // Any weight W >= Threshold can be replaced with W - CM. |
| APInt Threshold = CM + Bitwidth; |
| assert(LHS.ult(Threshold) && RHS.ult(Threshold) && "Weights not reduced!"); |
| // For Bitwidth 4 or more the following sum does not overflow. |
| LHS += RHS; |
| while (LHS.uge(Threshold)) |
| LHS -= CM; |
| } else { |
| // To avoid problems with overflow do everything the same as above but using |
| // a larger type. |
| unsigned CM = 1U << CarmichaelShift(Bitwidth); |
| unsigned Threshold = CM + Bitwidth; |
| assert(LHS.getZExtValue() < Threshold && RHS.getZExtValue() < Threshold && |
| "Weights not reduced!"); |
| unsigned Total = LHS.getZExtValue() + RHS.getZExtValue(); |
| while (Total >= Threshold) |
| Total -= CM; |
| LHS = Total; |
| } |
| } |
| |
| /// EvaluateRepeatedConstant - Compute C op C op ... op C where the constant C |
| /// is repeated Weight times. |
| static Constant *EvaluateRepeatedConstant(unsigned Opcode, Constant *C, |
| APInt Weight) { |
| // For addition the result can be efficiently computed as the product of the |
| // constant and the weight. |
| if (Opcode == Instruction::Add) |
| return ConstantExpr::getMul(C, ConstantInt::get(C->getContext(), Weight)); |
| |
| // The weight might be huge, so compute by repeated squaring to ensure that |
| // compile time is proportional to the logarithm of the weight. |
| Constant *Result = 0; |
| Constant *Power = C; // Successively C, C op C, (C op C) op (C op C) etc. |
| // Visit the bits in Weight. |
| while (Weight != 0) { |
| // If the current bit in Weight is non-zero do Result = Result op Power. |
| if (Weight[0]) |
| Result = Result ? ConstantExpr::get(Opcode, Result, Power) : Power; |
| // Move on to the next bit if any more are non-zero. |
| Weight = Weight.lshr(1); |
| if (Weight.isMinValue()) |
| break; |
| // Square the power. |
| Power = ConstantExpr::get(Opcode, Power, Power); |
| } |
| |
| assert(Result && "Only positive weights supported!"); |
| return Result; |
| } |
| |
| typedef std::pair<Value*, APInt> RepeatedValue; |
| |
| /// LinearizeExprTree - Given an associative binary expression, return the leaf |
| /// nodes in Ops along with their weights (how many times the leaf occurs). The |
| /// original expression is the same as |
| /// (Ops[0].first op Ops[0].first op ... Ops[0].first) <- Ops[0].second times |
| /// op |
| /// (Ops[1].first op Ops[1].first op ... Ops[1].first) <- Ops[1].second times |
| /// op |
| /// ... |
| /// op |
| /// (Ops[N].first op Ops[N].first op ... Ops[N].first) <- Ops[N].second times |
| /// |
| /// Note that the values Ops[0].first, ..., Ops[N].first are all distinct, and |
| /// they are all non-constant except possibly for the last one, which if it is |
| /// constant will have weight one (Ops[N].second === 1). |
| /// |
| /// This routine may modify the function, in which case it returns 'true'. The |
| /// changes it makes may well be destructive, changing the value computed by 'I' |
| /// to something completely different. Thus if the routine returns 'true' then |
| /// you MUST either replace I with a new expression computed from the Ops array, |
| /// or use RewriteExprTree to put the values back in. |
| /// |
| /// A leaf node is either not a binary operation of the same kind as the root |
| /// node 'I' (i.e. is not a binary operator at all, or is, but with a different |
| /// opcode), or is the same kind of binary operator but has a use which either |
| /// does not belong to the expression, or does belong to the expression but is |
| /// a leaf node. Every leaf node has at least one use that is a non-leaf node |
| /// of the expression, while for non-leaf nodes (except for the root 'I') every |
| /// use is a non-leaf node of the expression. |
| /// |
| /// For example: |
| /// expression graph node names |
| /// |
| /// + | I |
| /// / \ | |
| /// + + | A, B |
| /// / \ / \ | |
| /// * + * | C, D, E |
| /// / \ / \ / \ | |
| /// + * | F, G |
| /// |
| /// The leaf nodes are C, E, F and G. The Ops array will contain (maybe not in |
| /// that order) (C, 1), (E, 1), (F, 2), (G, 2). |
| /// |
| /// The expression is maximal: if some instruction is a binary operator of the |
| /// same kind as 'I', and all of its uses are non-leaf nodes of the expression, |
| /// then the instruction also belongs to the expression, is not a leaf node of |
| /// it, and its operands also belong to the expression (but may be leaf nodes). |
| /// |
| /// NOTE: This routine will set operands of non-leaf non-root nodes to undef in |
| /// order to ensure that every non-root node in the expression has *exactly one* |
| /// use by a non-leaf node of the expression. This destruction means that the |
| /// caller MUST either replace 'I' with a new expression or use something like |
| /// RewriteExprTree to put the values back in if the routine indicates that it |
| /// made a change by returning 'true'. |
| /// |
| /// In the above example either the right operand of A or the left operand of B |
| /// will be replaced by undef. If it is B's operand then this gives: |
| /// |
| /// + | I |
| /// / \ | |
| /// + + | A, B - operand of B replaced with undef |
| /// / \ \ | |
| /// * + * | C, D, E |
| /// / \ / \ / \ | |
| /// + * | F, G |
| /// |
| /// Note that such undef operands can only be reached by passing through 'I'. |
| /// For example, if you visit operands recursively starting from a leaf node |
| /// then you will never see such an undef operand unless you get back to 'I', |
| /// which requires passing through a phi node. |
| /// |
| /// Note that this routine may also mutate binary operators of the wrong type |
| /// that have all uses inside the expression (i.e. only used by non-leaf nodes |
| /// of the expression) if it can turn them into binary operators of the right |
| /// type and thus make the expression bigger. |
| |
| static bool LinearizeExprTree(BinaryOperator *I, |
| SmallVectorImpl<RepeatedValue> &Ops) { |
| DEBUG(dbgs() << "LINEARIZE: " << *I << '\n'); |
| unsigned Bitwidth = I->getType()->getScalarType()->getPrimitiveSizeInBits(); |
| unsigned Opcode = I->getOpcode(); |
| assert(Instruction::isAssociative(Opcode) && |
| Instruction::isCommutative(Opcode) && |
| "Expected an associative and commutative operation!"); |
| |
| // Visit all operands of the expression, keeping track of their weight (the |
| // number of paths from the expression root to the operand, or if you like |
| // the number of times that operand occurs in the linearized expression). |
| // For example, if I = X + A, where X = A + B, then I, X and B have weight 1 |
| // while A has weight two. |
| |
| // Worklist of non-leaf nodes (their operands are in the expression too) along |
| // with their weights, representing a certain number of paths to the operator. |
| // If an operator occurs in the worklist multiple times then we found multiple |
| // ways to get to it. |
| SmallVector<std::pair<BinaryOperator*, APInt>, 8> Worklist; // (Op, Weight) |
| Worklist.push_back(std::make_pair(I, APInt(Bitwidth, 1))); |
| bool MadeChange = false; |
| |
| // Leaves of the expression are values that either aren't the right kind of |
| // operation (eg: a constant, or a multiply in an add tree), or are, but have |
| // some uses that are not inside the expression. For example, in I = X + X, |
| // X = A + B, the value X has two uses (by I) that are in the expression. If |
| // X has any other uses, for example in a return instruction, then we consider |
| // X to be a leaf, and won't analyze it further. When we first visit a value, |
| // if it has more than one use then at first we conservatively consider it to |
| // be a leaf. Later, as the expression is explored, we may discover some more |
| // uses of the value from inside the expression. If all uses turn out to be |
| // from within the expression (and the value is a binary operator of the right |
| // kind) then the value is no longer considered to be a leaf, and its operands |
| // are explored. |
| |
| // Leaves - Keeps track of the set of putative leaves as well as the number of |
| // paths to each leaf seen so far. |
| typedef SmallMap<Value*, APInt, 8> LeafMap; |
| LeafMap Leaves; // Leaf -> Total weight so far. |
| SmallVector<Value*, 8> LeafOrder; // Ensure deterministic leaf output order. |
| |
| #ifndef NDEBUG |
| SmallPtrSet<Value*, 8> Visited; // For sanity checking the iteration scheme. |
| #endif |
| while (!Worklist.empty()) { |
| std::pair<BinaryOperator*, APInt> P = Worklist.pop_back_val(); |
| I = P.first; // We examine the operands of this binary operator. |
| |
| for (unsigned OpIdx = 0; OpIdx < 2; ++OpIdx) { // Visit operands. |
| Value *Op = I->getOperand(OpIdx); |
| APInt Weight = P.second; // Number of paths to this operand. |
| DEBUG(dbgs() << "OPERAND: " << *Op << " (" << Weight << ")\n"); |
| assert(!Op->use_empty() && "No uses, so how did we get to it?!"); |
| |
| // If this is a binary operation of the right kind with only one use then |
| // add its operands to the expression. |
| if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) { |
| assert(Visited.insert(Op) && "Not first visit!"); |
| DEBUG(dbgs() << "DIRECT ADD: " << *Op << " (" << Weight << ")\n"); |
| Worklist.push_back(std::make_pair(BO, Weight)); |
| continue; |
| } |
| |
| // Appears to be a leaf. Is the operand already in the set of leaves? |
| LeafMap::iterator It = Leaves.find(Op); |
| if (It == Leaves.end()) { |
| // Not in the leaf map. Must be the first time we saw this operand. |
| assert(Visited.insert(Op) && "Not first visit!"); |
| if (!Op->hasOneUse()) { |
| // This value has uses not accounted for by the expression, so it is |
| // not safe to modify. Mark it as being a leaf. |
| DEBUG(dbgs() << "ADD USES LEAF: " << *Op << " (" << Weight << ")\n"); |
| LeafOrder.push_back(Op); |
| Leaves[Op] = Weight; |
| continue; |
| } |
| // No uses outside the expression, try morphing it. |
| } else if (It != Leaves.end()) { |
| // Already in the leaf map. |
| assert(Visited.count(Op) && "In leaf map but not visited!"); |
| |
| // Update the number of paths to the leaf. |
| IncorporateWeight(It->second, Weight, Opcode); |
| |
| // The leaf already has one use from inside the expression. As we want |
| // exactly one such use, drop this new use of the leaf. |
| assert(!Op->hasOneUse() && "Only one use, but we got here twice!"); |
| I->setOperand(OpIdx, UndefValue::get(I->getType())); |
| MadeChange = true; |
| |
| // If the leaf is a binary operation of the right kind and we now see |
| // that its multiple original uses were in fact all by nodes belonging |
| // to the expression, then no longer consider it to be a leaf and add |
| // its operands to the expression. |
| if (BinaryOperator *BO = isReassociableOp(Op, Opcode)) { |
| DEBUG(dbgs() << "UNLEAF: " << *Op << " (" << It->second << ")\n"); |
| Worklist.push_back(std::make_pair(BO, It->second)); |
| Leaves.erase(It); |
| continue; |
| } |
| |
| // If we still have uses that are not accounted for by the expression |
| // then it is not safe to modify the value. |
| if (!Op->hasOneUse()) |
| continue; |
| |
| // No uses outside the expression, try morphing it. |
| Weight = It->second; |
| Leaves.erase(It); // Since the value may be morphed below. |
| } |
| |
| // At this point we have a value which, first of all, is not a binary |
| // expression of the right kind, and secondly, is only used inside the |
| // expression. This means that it can safely be modified. See if we |
| // can usefully morph it into an expression of the right kind. |
| assert((!isa<Instruction>(Op) || |
| cast<Instruction>(Op)->getOpcode() != Opcode) && |
| "Should have been handled above!"); |
| assert(Op->hasOneUse() && "Has uses outside the expression tree!"); |
| |
| // If this is a multiply expression, turn any internal negations into |
| // multiplies by -1 so they can be reassociated. |
| BinaryOperator *BO = dyn_cast<BinaryOperator>(Op); |
| if (Opcode == Instruction::Mul && BO && BinaryOperator::isNeg(BO)) { |
| DEBUG(dbgs() << "MORPH LEAF: " << *Op << " (" << Weight << ") TO "); |
| BO = LowerNegateToMultiply(BO); |
| DEBUG(dbgs() << *BO << 'n'); |
| Worklist.push_back(std::make_pair(BO, Weight)); |
| MadeChange = true; |
| continue; |
| } |
| |
| // Failed to morph into an expression of the right type. This really is |
| // a leaf. |
| DEBUG(dbgs() << "ADD LEAF: " << *Op << " (" << Weight << ")\n"); |
| assert(!isReassociableOp(Op, Opcode) && "Value was morphed?"); |
| LeafOrder.push_back(Op); |
| Leaves[Op] = Weight; |
| } |
| } |
| |
| // The leaves, repeated according to their weights, represent the linearized |
| // form of the expression. |
| Constant *Cst = 0; // Accumulate constants here. |
| for (unsigned i = 0, e = LeafOrder.size(); i != e; ++i) { |
| Value *V = LeafOrder[i]; |
| LeafMap::iterator It = Leaves.find(V); |
| if (It == Leaves.end()) |
| // Node initially thought to be a leaf wasn't. |
| continue; |
| assert(!isReassociableOp(V, Opcode) && "Shouldn't be a leaf!"); |
| APInt Weight = It->second; |
| if (Weight.isMinValue()) |
| // Leaf already output or weight reduction eliminated it. |
| continue; |
| // Ensure the leaf is only output once. |
| It->second = 0; |
| // Glob all constants together into Cst. |
| if (Constant *C = dyn_cast<Constant>(V)) { |
| C = EvaluateRepeatedConstant(Opcode, C, Weight); |
| Cst = Cst ? ConstantExpr::get(Opcode, Cst, C) : C; |
| continue; |
| } |
| // Add non-constant |
| Ops.push_back(std::make_pair(V, Weight)); |
| } |
| |
| // Add any constants back into Ops, all globbed together and reduced to having |
| // weight 1 for the convenience of users. |
| if (Cst && Cst != ConstantExpr::getBinOpIdentity(Opcode, I->getType())) |
| Ops.push_back(std::make_pair(Cst, APInt(Bitwidth, 1))); |
| |
| // For nilpotent operations or addition there may be no operands, for example |
| // because the expression was "X xor X" or consisted of 2^Bitwidth additions: |
| // in both cases the weight reduces to 0 causing the value to be skipped. |
| if (Ops.empty()) { |
| Constant *Identity = ConstantExpr::getBinOpIdentity(Opcode, I->getType()); |
| Ops.push_back(std::make_pair(Identity, APInt(Bitwidth, 1))); |
| } |
| |
| return MadeChange; |
| } |
| |
| // RewriteExprTree - Now that the operands for this expression tree are |
| // linearized and optimized, emit them in-order. |
| void Reassociate::RewriteExprTree(BinaryOperator *I, |
| SmallVectorImpl<ValueEntry> &Ops) { |
| assert(Ops.size() > 1 && "Single values should be used directly!"); |
| |
| // Since our optimizations never increase the number of operations, the new |
| // expression can always be written by reusing the existing binary operators |
| // from the original expression tree, without creating any new instructions, |
| // though the rewritten expression may have a completely different topology. |
| // We take care to not change anything if the new expression will be the same |
| // as the original. If more than trivial changes (like commuting operands) |
| // were made then we are obliged to clear out any optional subclass data like |
| // nsw flags. |
| |
| /// NodesToRewrite - Nodes from the original expression available for writing |
| /// the new expression into. |
| SmallVector<BinaryOperator*, 8> NodesToRewrite; |
| unsigned Opcode = I->getOpcode(); |
| NodesToRewrite.push_back(I); |
| |
| // ExpressionChanged - Non-null if the rewritten expression differs from the |
| // original in some non-trivial way, requiring the clearing of optional flags. |
| // Flags are cleared from the operator in ExpressionChanged up to I inclusive. |
| BinaryOperator *ExpressionChanged = 0; |
| BinaryOperator *Previous; |
| BinaryOperator *Op = 0; |
| for (unsigned i = 0, e = Ops.size(); i != e; ++i) { |
| assert(!NodesToRewrite.empty() && |
| "Optimized expressions has more nodes than original!"); |
| Previous = Op; Op = NodesToRewrite.pop_back_val(); |
| if (ExpressionChanged) |
| // Compactify the tree instructions together with each other to guarantee |
| // that the expression tree is dominated by all of Ops. |
| Op->moveBefore(Previous); |
| |
| // The last operation (which comes earliest in the IR) is special as both |
| // operands will come from Ops, rather than just one with the other being |
| // a subexpression. |
| if (i+2 == Ops.size()) { |
| Value *NewLHS = Ops[i].Op; |
| Value *NewRHS = Ops[i+1].Op; |
| Value *OldLHS = Op->getOperand(0); |
| Value *OldRHS = Op->getOperand(1); |
| |
| if (NewLHS == OldLHS && NewRHS == OldRHS) |
| // Nothing changed, leave it alone. |
| break; |
| |
| if (NewLHS == OldRHS && NewRHS == OldLHS) { |
| // The order of the operands was reversed. Swap them. |
| DEBUG(dbgs() << "RA: " << *Op << '\n'); |
| Op->swapOperands(); |
| DEBUG(dbgs() << "TO: " << *Op << '\n'); |
| MadeChange = true; |
| ++NumChanged; |
| break; |
| } |
| |
| // The new operation differs non-trivially from the original. Overwrite |
| // the old operands with the new ones. |
| DEBUG(dbgs() << "RA: " << *Op << '\n'); |
| if (NewLHS != OldLHS) { |
| if (BinaryOperator *BO = isReassociableOp(OldLHS, Opcode)) |
| NodesToRewrite.push_back(BO); |
| Op->setOperand(0, NewLHS); |
| } |
| if (NewRHS != OldRHS) { |
| if (BinaryOperator *BO = isReassociableOp(OldRHS, Opcode)) |
| NodesToRewrite.push_back(BO); |
| Op->setOperand(1, NewRHS); |
| } |
| DEBUG(dbgs() << "TO: " << *Op << '\n'); |
| |
| ExpressionChanged = Op; |
| MadeChange = true; |
| ++NumChanged; |
| |
| break; |
| } |
| |
| // Not the last operation. The left-hand side will be a sub-expression |
| // while the right-hand side will be the current element of Ops. |
| Value *NewRHS = Ops[i].Op; |
| if (NewRHS != Op->getOperand(1)) { |
| DEBUG(dbgs() << "RA: " << *Op << '\n'); |
| if (NewRHS == Op->getOperand(0)) { |
| // The new right-hand side was already present as the left operand. If |
| // we are lucky then swapping the operands will sort out both of them. |
| Op->swapOperands(); |
| } else { |
| // Overwrite with the new right-hand side. |
| if (BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode)) |
| NodesToRewrite.push_back(BO); |
| Op->setOperand(1, NewRHS); |
| ExpressionChanged = Op; |
| } |
| DEBUG(dbgs() << "TO: " << *Op << '\n'); |
| MadeChange = true; |
| ++NumChanged; |
| } |
| |
| // Now deal with the left-hand side. If this is already an operation node |
| // from the original expression then just rewrite the rest of the expression |
| // into it. |
| if (BinaryOperator *BO = isReassociableOp(Op->getOperand(0), Opcode)) { |
| NodesToRewrite.push_back(BO); |
| continue; |
| } |
| |
| // Otherwise, grab a spare node from the original expression and use that as |
| // the left-hand side. |
| assert(!NodesToRewrite.empty() && |
| "Optimized expressions has more nodes than original!"); |
| DEBUG(dbgs() << "RA: " << *Op << '\n'); |
| Op->setOperand(0, NodesToRewrite.back()); |
| DEBUG(dbgs() << "TO: " << *Op << '\n'); |
| ExpressionChanged = Op; |
| MadeChange = true; |
| ++NumChanged; |
| } |
| |
| // If the expression changed non-trivially then clear out all subclass data |
| // starting from the operator specified in ExpressionChanged. |
| if (ExpressionChanged) { |
| do { |
| ExpressionChanged->clearSubclassOptionalData(); |
| if (ExpressionChanged == I) |
| break; |
| ExpressionChanged = cast<BinaryOperator>(*ExpressionChanged->use_begin()); |
| } while (1); |
| } |
| |
| // Throw away any left over nodes from the original expression. |
| for (unsigned i = 0, e = NodesToRewrite.size(); i != e; ++i) |
| RedoInsts.insert(NodesToRewrite[i]); |
| } |
| |
| /// NegateValue - Insert instructions before the instruction pointed to by BI, |
| /// that computes the negative version of the value specified. The negative |
| /// version of the value is returned, and BI is left pointing at the instruction |
| /// that should be processed next by the reassociation pass. |
| static Value *NegateValue(Value *V, Instruction *BI) { |
| if (Constant *C = dyn_cast<Constant>(V)) |
| return ConstantExpr::getNeg(C); |
| |
| // We are trying to expose opportunity for reassociation. One of the things |
| // that we want to do to achieve this is to push a negation as deep into an |
| // expression chain as possible, to expose the add instructions. In practice, |
| // this means that we turn this: |
| // X = -(A+12+C+D) into X = -A + -12 + -C + -D = -12 + -A + -C + -D |
| // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate |
| // the constants. We assume that instcombine will clean up the mess later if |
| // we introduce tons of unnecessary negation instructions. |
| // |
| if (BinaryOperator *I = isReassociableOp(V, Instruction::Add)) { |
| // Push the negates through the add. |
| I->setOperand(0, NegateValue(I->getOperand(0), BI)); |
| I->setOperand(1, NegateValue(I->getOperand(1), BI)); |
| |
| // We must move the add instruction here, because the neg instructions do |
| // not dominate the old add instruction in general. By moving it, we are |
| // assured that the neg instructions we just inserted dominate the |
| // instruction we are about to insert after them. |
| // |
| I->moveBefore(BI); |
| I->setName(I->getName()+".neg"); |
| return I; |
| } |
| |
| // Okay, we need to materialize a negated version of V with an instruction. |
| // Scan the use lists of V to see if we have one already. |
| for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){ |
| User *U = *UI; |
| if (!BinaryOperator::isNeg(U)) continue; |
| |
| // We found one! Now we have to make sure that the definition dominates |
| // this use. We do this by moving it to the entry block (if it is a |
| // non-instruction value) or right after the definition. These negates will |
| // be zapped by reassociate later, so we don't need much finesse here. |
| BinaryOperator *TheNeg = cast<BinaryOperator>(U); |
| |
| // Verify that the negate is in this function, V might be a constant expr. |
| if (TheNeg->getParent()->getParent() != BI->getParent()->getParent()) |
| continue; |
| |
| BasicBlock::iterator InsertPt; |
| if (Instruction *InstInput = dyn_cast<Instruction>(V)) { |
| if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) { |
| InsertPt = II->getNormalDest()->begin(); |
| } else { |
| InsertPt = InstInput; |
| ++InsertPt; |
| } |
| while (isa<PHINode>(InsertPt)) ++InsertPt; |
| } else { |
| InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin(); |
| } |
| TheNeg->moveBefore(InsertPt); |
| return TheNeg; |
| } |
| |
| // Insert a 'neg' instruction that subtracts the value from zero to get the |
| // negation. |
| return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI); |
| } |
| |
| /// ShouldBreakUpSubtract - Return true if we should break up this subtract of |
| /// X-Y into (X + -Y). |
| static bool ShouldBreakUpSubtract(Instruction *Sub) { |
| // If this is a negation, we can't split it up! |
| if (BinaryOperator::isNeg(Sub)) |
| return false; |
| |
| // Don't bother to break this up unless either the LHS is an associable add or |
| // subtract or if this is only used by one. |
| if (isReassociableOp(Sub->getOperand(0), Instruction::Add) || |
| isReassociableOp(Sub->getOperand(0), Instruction::Sub)) |
| return true; |
| if (isReassociableOp(Sub->getOperand(1), Instruction::Add) || |
| isReassociableOp(Sub->getOperand(1), Instruction::Sub)) |
| return true; |
| if (Sub->hasOneUse() && |
| (isReassociableOp(Sub->use_back(), Instruction::Add) || |
| isReassociableOp(Sub->use_back(), Instruction::Sub))) |
| return true; |
| |
| return false; |
| } |
| |
| /// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is |
| /// only used by an add, transform this into (X+(0-Y)) to promote better |
| /// reassociation. |
| static BinaryOperator *BreakUpSubtract(Instruction *Sub) { |
| // Convert a subtract into an add and a neg instruction. This allows sub |
| // instructions to be commuted with other add instructions. |
| // |
| // Calculate the negative value of Operand 1 of the sub instruction, |
| // and set it as the RHS of the add instruction we just made. |
| // |
| Value *NegVal = NegateValue(Sub->getOperand(1), Sub); |
| BinaryOperator *New = |
| BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub); |
| Sub->setOperand(0, Constant::getNullValue(Sub->getType())); // Drop use of op. |
| Sub->setOperand(1, Constant::getNullValue(Sub->getType())); // Drop use of op. |
| New->takeName(Sub); |
| |
| // Everyone now refers to the add instruction. |
| Sub->replaceAllUsesWith(New); |
| New->setDebugLoc(Sub->getDebugLoc()); |
| |
| DEBUG(dbgs() << "Negated: " << *New << '\n'); |
| return New; |
| } |
| |
| /// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used |
| /// by one, change this into a multiply by a constant to assist with further |
| /// reassociation. |
| static BinaryOperator *ConvertShiftToMul(Instruction *Shl) { |
| Constant *MulCst = ConstantInt::get(Shl->getType(), 1); |
| MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1))); |
| |
| BinaryOperator *Mul = |
| BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl); |
| Shl->setOperand(0, UndefValue::get(Shl->getType())); // Drop use of op. |
| Mul->takeName(Shl); |
| Shl->replaceAllUsesWith(Mul); |
| Mul->setDebugLoc(Shl->getDebugLoc()); |
| return Mul; |
| } |
| |
| /// FindInOperandList - Scan backwards and forwards among values with the same |
| /// rank as element i to see if X exists. If X does not exist, return i. This |
| /// is useful when scanning for 'x' when we see '-x' because they both get the |
| /// same rank. |
| static unsigned FindInOperandList(SmallVectorImpl<ValueEntry> &Ops, unsigned i, |
| Value *X) { |
| unsigned XRank = Ops[i].Rank; |
| unsigned e = Ops.size(); |
| for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j) |
| if (Ops[j].Op == X) |
| return j; |
| // Scan backwards. |
| for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j) |
| if (Ops[j].Op == X) |
| return j; |
| return i; |
| } |
| |
| /// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together |
| /// and returning the result. Insert the tree before I. |
| static Value *EmitAddTreeOfValues(Instruction *I, |
| SmallVectorImpl<WeakVH> &Ops){ |
| if (Ops.size() == 1) return Ops.back(); |
| |
| Value *V1 = Ops.back(); |
| Ops.pop_back(); |
| Value *V2 = EmitAddTreeOfValues(I, Ops); |
| return BinaryOperator::CreateAdd(V2, V1, "tmp", I); |
| } |
| |
| /// RemoveFactorFromExpression - If V is an expression tree that is a |
| /// multiplication sequence, and if this sequence contains a multiply by Factor, |
| /// remove Factor from the tree and return the new tree. |
| Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) { |
| BinaryOperator *BO = isReassociableOp(V, Instruction::Mul); |
| if (!BO) return 0; |
| |
| SmallVector<RepeatedValue, 8> Tree; |
| MadeChange |= LinearizeExprTree(BO, Tree); |
| SmallVector<ValueEntry, 8> Factors; |
| Factors.reserve(Tree.size()); |
| for (unsigned i = 0, e = Tree.size(); i != e; ++i) { |
| RepeatedValue E = Tree[i]; |
| Factors.append(E.second.getZExtValue(), |
| ValueEntry(getRank(E.first), E.first)); |
| } |
| |
| bool FoundFactor = false; |
| bool NeedsNegate = false; |
| for (unsigned i = 0, e = Factors.size(); i != e; ++i) { |
| if (Factors[i].Op == Factor) { |
| FoundFactor = true; |
| Factors.erase(Factors.begin()+i); |
| break; |
| } |
| |
| // If this is a negative version of this factor, remove it. |
| if (ConstantInt *FC1 = dyn_cast<ConstantInt>(Factor)) |
| if (ConstantInt *FC2 = dyn_cast<ConstantInt>(Factors[i].Op)) |
| if (FC1->getValue() == -FC2->getValue()) { |
| FoundFactor = NeedsNegate = true; |
| Factors.erase(Factors.begin()+i); |
| break; |
| } |
| } |
| |
| if (!FoundFactor) { |
| // Make sure to restore the operands to the expression tree. |
| RewriteExprTree(BO, Factors); |
| return 0; |
| } |
| |
| BasicBlock::iterator InsertPt = BO; ++InsertPt; |
| |
| // If this was just a single multiply, remove the multiply and return the only |
| // remaining operand. |
| if (Factors.size() == 1) { |
| RedoInsts.insert(BO); |
| V = Factors[0].Op; |
| } else { |
| RewriteExprTree(BO, Factors); |
| V = BO; |
| } |
| |
| if (NeedsNegate) |
| V = BinaryOperator::CreateNeg(V, "neg", InsertPt); |
| |
| return V; |
| } |
| |
| /// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively |
| /// add its operands as factors, otherwise add V to the list of factors. |
| /// |
| /// Ops is the top-level list of add operands we're trying to factor. |
| static void FindSingleUseMultiplyFactors(Value *V, |
| SmallVectorImpl<Value*> &Factors, |
| const SmallVectorImpl<ValueEntry> &Ops) { |
| BinaryOperator *BO = isReassociableOp(V, Instruction::Mul); |
| if (!BO) { |
| Factors.push_back(V); |
| return; |
| } |
| |
| // Otherwise, add the LHS and RHS to the list of factors. |
| FindSingleUseMultiplyFactors(BO->getOperand(1), Factors, Ops); |
| FindSingleUseMultiplyFactors(BO->getOperand(0), Factors, Ops); |
| } |
| |
| /// OptimizeAndOrXor - Optimize a series of operands to an 'and', 'or', or 'xor' |
| /// instruction. This optimizes based on identities. If it can be reduced to |
| /// a single Value, it is returned, otherwise the Ops list is mutated as |
| /// necessary. |
| static Value *OptimizeAndOrXor(unsigned Opcode, |
| SmallVectorImpl<ValueEntry> &Ops) { |
| // Scan the operand lists looking for X and ~X pairs, along with X,X pairs. |
| // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1. |
| for (unsigned i = 0, e = Ops.size(); i != e; ++i) { |
| // First, check for X and ~X in the operand list. |
| assert(i < Ops.size()); |
| if (BinaryOperator::isNot(Ops[i].Op)) { // Cannot occur for ^. |
| Value *X = BinaryOperator::getNotArgument(Ops[i].Op); |
| unsigned FoundX = FindInOperandList(Ops, i, X); |
| if (FoundX != i) { |
| if (Opcode == Instruction::And) // ...&X&~X = 0 |
| return Constant::getNullValue(X->getType()); |
| |
| if (Opcode == Instruction::Or) // ...|X|~X = -1 |
| return Constant::getAllOnesValue(X->getType()); |
| } |
| } |
| |
| // Next, check for duplicate pairs of values, which we assume are next to |
| // each other, due to our sorting criteria. |
| assert(i < Ops.size()); |
| if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) { |
| if (Opcode == Instruction::And || Opcode == Instruction::Or) { |
| // Drop duplicate values for And and Or. |
| Ops.erase(Ops.begin()+i); |
| --i; --e; |
| ++NumAnnihil; |
| continue; |
| } |
| |
| // Drop pairs of values for Xor. |
| assert(Opcode == Instruction::Xor); |
| if (e == 2) |
| return Constant::getNullValue(Ops[0].Op->getType()); |
| |
| // Y ^ X^X -> Y |
| Ops.erase(Ops.begin()+i, Ops.begin()+i+2); |
| i -= 1; e -= 2; |
| ++NumAnnihil; |
| } |
| } |
| return 0; |
| } |
| |
| /// OptimizeAdd - Optimize a series of operands to an 'add' instruction. This |
| /// optimizes based on identities. If it can be reduced to a single Value, it |
| /// is returned, otherwise the Ops list is mutated as necessary. |
| Value *Reassociate::OptimizeAdd(Instruction *I, |
| SmallVectorImpl<ValueEntry> &Ops) { |
| // Scan the operand lists looking for X and -X pairs. If we find any, we |
| // can simplify the expression. X+-X == 0. While we're at it, scan for any |
| // duplicates. We want to canonicalize Y+Y+Y+Z -> 3*Y+Z. |
| // |
| // TODO: We could handle "X + ~X" -> "-1" if we wanted, since "-X = ~X+1". |
| // |
| for (unsigned i = 0, e = Ops.size(); i != e; ++i) { |
| Value *TheOp = Ops[i].Op; |
| // Check to see if we've seen this operand before. If so, we factor all |
| // instances of the operand together. Due to our sorting criteria, we know |
| // that these need to be next to each other in the vector. |
| if (i+1 != Ops.size() && Ops[i+1].Op == TheOp) { |
| // Rescan the list, remove all instances of this operand from the expr. |
| unsigned NumFound = 0; |
| do { |
| Ops.erase(Ops.begin()+i); |
| ++NumFound; |
| } while (i != Ops.size() && Ops[i].Op == TheOp); |
| |
| DEBUG(errs() << "\nFACTORING [" << NumFound << "]: " << *TheOp << '\n'); |
| ++NumFactor; |
| |
| // Insert a new multiply. |
| Value *Mul = ConstantInt::get(cast<IntegerType>(I->getType()), NumFound); |
| Mul = BinaryOperator::CreateMul(TheOp, Mul, "factor", I); |
| |
| // Now that we have inserted a multiply, optimize it. This allows us to |
| // handle cases that require multiple factoring steps, such as this: |
| // (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6 |
| RedoInsts.insert(cast<Instruction>(Mul)); |
| |
| // If every add operand was a duplicate, return the multiply. |
| if (Ops.empty()) |
| return Mul; |
| |
| // Otherwise, we had some input that didn't have the dupe, such as |
| // "A + A + B" -> "A*2 + B". Add the new multiply to the list of |
| // things being added by this operation. |
| Ops.insert(Ops.begin(), ValueEntry(getRank(Mul), Mul)); |
| |
| --i; |
| e = Ops.size(); |
| continue; |
| } |
| |
| // Check for X and -X in the operand list. |
| if (!BinaryOperator::isNeg(TheOp)) |
| continue; |
| |
| Value *X = BinaryOperator::getNegArgument(TheOp); |
| unsigned FoundX = FindInOperandList(Ops, i, X); |
| if (FoundX == i) |
| continue; |
| |
| // Remove X and -X from the operand list. |
| if (Ops.size() == 2) |
| return Constant::getNullValue(X->getType()); |
| |
| Ops.erase(Ops.begin()+i); |
| if (i < FoundX) |
| --FoundX; |
| else |
| --i; // Need to back up an extra one. |
| Ops.erase(Ops.begin()+FoundX); |
| ++NumAnnihil; |
| --i; // Revisit element. |
| e -= 2; // Removed two elements. |
| } |
| |
| // Scan the operand list, checking to see if there are any common factors |
| // between operands. Consider something like A*A+A*B*C+D. We would like to |
| // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies. |
| // To efficiently find this, we count the number of times a factor occurs |
| // for any ADD operands that are MULs. |
| DenseMap<Value*, unsigned> FactorOccurrences; |
| |
| // Keep track of each multiply we see, to avoid triggering on (X*4)+(X*4) |
| // where they are actually the same multiply. |
| unsigned MaxOcc = 0; |
| Value *MaxOccVal = 0; |
| for (unsigned i = 0, e = Ops.size(); i != e; ++i) { |
| BinaryOperator *BOp = isReassociableOp(Ops[i].Op, Instruction::Mul); |
| if (!BOp) |
| continue; |
| |
| // Compute all of the factors of this added value. |
| SmallVector<Value*, 8> Factors; |
| FindSingleUseMultiplyFactors(BOp, Factors, Ops); |
| assert(Factors.size() > 1 && "Bad linearize!"); |
| |
| // Add one to FactorOccurrences for each unique factor in this op. |
| SmallPtrSet<Value*, 8> Duplicates; |
| for (unsigned i = 0, e = Factors.size(); i != e; ++i) { |
| Value *Factor = Factors[i]; |
| if (!Duplicates.insert(Factor)) continue; |
| |
| unsigned Occ = ++FactorOccurrences[Factor]; |
| if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; } |
| |
| // If Factor is a negative constant, add the negated value as a factor |
| // because we can percolate the negate out. Watch for minint, which |
| // cannot be positivified. |
| if (ConstantInt *CI = dyn_cast<ConstantInt>(Factor)) |
| if (CI->isNegative() && !CI->isMinValue(true)) { |
| Factor = ConstantInt::get(CI->getContext(), -CI->getValue()); |
| assert(!Duplicates.count(Factor) && |
| "Shouldn't have two constant factors, missed a canonicalize"); |
| |
| unsigned Occ = ++FactorOccurrences[Factor]; |
| if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; } |
| } |
| } |
| } |
| |
| // If any factor occurred more than one time, we can pull it out. |
| if (MaxOcc > 1) { |
| DEBUG(errs() << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << '\n'); |
| ++NumFactor; |
| |
| // Create a new instruction that uses the MaxOccVal twice. If we don't do |
| // this, we could otherwise run into situations where removing a factor |
| // from an expression will drop a use of maxocc, and this can cause |
| // RemoveFactorFromExpression on successive values to behave differently. |
| Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal); |
| SmallVector<WeakVH, 4> NewMulOps; |
| for (unsigned i = 0; i != Ops.size(); ++i) { |
| // Only try to remove factors from expressions we're allowed to. |
| BinaryOperator *BOp = isReassociableOp(Ops[i].Op, Instruction::Mul); |
| if (!BOp) |
| continue; |
| |
| if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) { |
| // The factorized operand may occur several times. Convert them all in |
| // one fell swoop. |
| for (unsigned j = Ops.size(); j != i;) { |
| --j; |
| if (Ops[j].Op == Ops[i].Op) { |
| NewMulOps.push_back(V); |
| Ops.erase(Ops.begin()+j); |
| } |
| } |
| --i; |
| } |
| } |
| |
| // No need for extra uses anymore. |
| delete DummyInst; |
| |
| unsigned NumAddedValues = NewMulOps.size(); |
| Value *V = EmitAddTreeOfValues(I, NewMulOps); |
| |
| // Now that we have inserted the add tree, optimize it. This allows us to |
| // handle cases that require multiple factoring steps, such as this: |
| // A*A*B + A*A*C --> A*(A*B+A*C) --> A*(A*(B+C)) |
| assert(NumAddedValues > 1 && "Each occurrence should contribute a value"); |
| (void)NumAddedValues; |
| if (Instruction *VI = dyn_cast<Instruction>(V)) |
| RedoInsts.insert(VI); |
| |
| // Create the multiply. |
| Instruction *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I); |
| |
| // Rerun associate on the multiply in case the inner expression turned into |
| // a multiply. We want to make sure that we keep things in canonical form. |
| RedoInsts.insert(V2); |
| |
| // If every add operand included the factor (e.g. "A*B + A*C"), then the |
| // entire result expression is just the multiply "A*(B+C)". |
| if (Ops.empty()) |
| return V2; |
| |
| // Otherwise, we had some input that didn't have the factor, such as |
| // "A*B + A*C + D" -> "A*(B+C) + D". Add the new multiply to the list of |
| // things being added by this operation. |
| Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2)); |
| } |
| |
| return 0; |
| } |
| |
| namespace { |
| /// \brief Predicate tests whether a ValueEntry's op is in a map. |
| struct IsValueInMap { |
| const DenseMap<Value *, unsigned> ⤅ |
| |
| IsValueInMap(const DenseMap<Value *, unsigned> &Map) : Map(Map) {} |
| |
| bool operator()(const ValueEntry &Entry) { |
| return Map.find(Entry.Op) != Map.end(); |
| } |
| }; |
| } |
| |
| /// \brief Build up a vector of value/power pairs factoring a product. |
| /// |
| /// Given a series of multiplication operands, build a vector of factors and |
| /// the powers each is raised to when forming the final product. Sort them in |
| /// the order of descending power. |
| /// |
| /// (x*x) -> [(x, 2)] |
| /// ((x*x)*x) -> [(x, 3)] |
| /// ((((x*y)*x)*y)*x) -> [(x, 3), (y, 2)] |
| /// |
| /// \returns Whether any factors have a power greater than one. |
| bool Reassociate::collectMultiplyFactors(SmallVectorImpl<ValueEntry> &Ops, |
| SmallVectorImpl<Factor> &Factors) { |
| // FIXME: Have Ops be (ValueEntry, Multiplicity) pairs, simplifying this. |
| // Compute the sum of powers of simplifiable factors. |
| unsigned FactorPowerSum = 0; |
| for (unsigned Idx = 1, Size = Ops.size(); Idx < Size; ++Idx) { |
| Value *Op = Ops[Idx-1].Op; |
| |
| // Count the number of occurrences of this value. |
| unsigned Count = 1; |
| for (; Idx < Size && Ops[Idx].Op == Op; ++Idx) |
| ++Count; |
| // Track for simplification all factors which occur 2 or more times. |
| if (Count > 1) |
| FactorPowerSum += Count; |
| } |
| |
| // We can only simplify factors if the sum of the powers of our simplifiable |
| // factors is 4 or higher. When that is the case, we will *always* have |
| // a simplification. This is an important invariant to prevent cyclicly |
| // trying to simplify already minimal formations. |
| if (FactorPowerSum < 4) |
| return false; |
| |
| // Now gather the simplifiable factors, removing them from Ops. |
| FactorPowerSum = 0; |
| for (unsigned Idx = 1; Idx < Ops.size(); ++Idx) { |
| Value *Op = Ops[Idx-1].Op; |
| |
| // Count the number of occurrences of this value. |
| unsigned Count = 1; |
| for (; Idx < Ops.size() && Ops[Idx].Op == Op; ++Idx) |
| ++Count; |
| if (Count == 1) |
| continue; |
| // Move an even number of occurrences to Factors. |
| Count &= ~1U; |
| Idx -= Count; |
| FactorPowerSum += Count; |
| Factors.push_back(Factor(Op, Count)); |
| Ops.erase(Ops.begin()+Idx, Ops.begin()+Idx+Count); |
| } |
| |
| // None of the adjustments above should have reduced the sum of factor powers |
| // below our mininum of '4'. |
| assert(FactorPowerSum >= 4); |
| |
| std::sort(Factors.begin(), Factors.end(), Factor::PowerDescendingSorter()); |
| return true; |
| } |
| |
| /// \brief Build a tree of multiplies, computing the product of Ops. |
| static Value *buildMultiplyTree(IRBuilder<> &Builder, |
| SmallVectorImpl<Value*> &Ops) { |
| if (Ops.size() == 1) |
| return Ops.back(); |
| |
| Value *LHS = Ops.pop_back_val(); |
| do { |
| LHS = Builder.CreateMul(LHS, Ops.pop_back_val()); |
| } while (!Ops.empty()); |
| |
| return LHS; |
| } |
| |
| /// \brief Build a minimal multiplication DAG for (a^x)*(b^y)*(c^z)*... |
| /// |
| /// Given a vector of values raised to various powers, where no two values are |
| /// equal and the powers are sorted in decreasing order, compute the minimal |
| /// DAG of multiplies to compute the final product, and return that product |
| /// value. |
| Value *Reassociate::buildMinimalMultiplyDAG(IRBuilder<> &Builder, |
| SmallVectorImpl<Factor> &Factors) { |
| assert(Factors[0].Power); |
| SmallVector<Value *, 4> OuterProduct; |
| for (unsigned LastIdx = 0, Idx = 1, Size = Factors.size(); |
| Idx < Size && Factors[Idx].Power > 0; ++Idx) { |
| if (Factors[Idx].Power != Factors[LastIdx].Power) { |
| LastIdx = Idx; |
| continue; |
| } |
| |
| // We want to multiply across all the factors with the same power so that |
| // we can raise them to that power as a single entity. Build a mini tree |
| // for that. |
| SmallVector<Value *, 4> InnerProduct; |
| InnerProduct.push_back(Factors[LastIdx].Base); |
| do { |
| InnerProduct.push_back(Factors[Idx].Base); |
| ++Idx; |
| } while (Idx < Size && Factors[Idx].Power == Factors[LastIdx].Power); |
| |
| // Reset the base value of the first factor to the new expression tree. |
| // We'll remove all the factors with the same power in a second pass. |
| Value *M = Factors[LastIdx].Base = buildMultiplyTree(Builder, InnerProduct); |
| if (Instruction *MI = dyn_cast<Instruction>(M)) |
| RedoInsts.insert(MI); |
| |
| LastIdx = Idx; |
| } |
| // Unique factors with equal powers -- we've folded them into the first one's |
| // base. |
| Factors.erase(std::unique(Factors.begin(), Factors.end(), |
| Factor::PowerEqual()), |
| Factors.end()); |
| |
| // Iteratively collect the base of each factor with an add power into the |
| // outer product, and halve each power in preparation for squaring the |
| // expression. |
| for (unsigned Idx = 0, Size = Factors.size(); Idx != Size; ++Idx) { |
| if (Factors[Idx].Power & 1) |
| OuterProduct.push_back(Factors[Idx].Base); |
| Factors[Idx].Power >>= 1; |
| } |
| if (Factors[0].Power) { |
| Value *SquareRoot = buildMinimalMultiplyDAG(Builder, Factors); |
| OuterProduct.push_back(SquareRoot); |
| OuterProduct.push_back(SquareRoot); |
| } |
| if (OuterProduct.size() == 1) |
| return OuterProduct.front(); |
| |
| Value *V = buildMultiplyTree(Builder, OuterProduct); |
| return V; |
| } |
| |
| Value *Reassociate::OptimizeMul(BinaryOperator *I, |
| SmallVectorImpl<ValueEntry> &Ops) { |
| // We can only optimize the multiplies when there is a chain of more than |
| // three, such that a balanced tree might require fewer total multiplies. |
| if (Ops.size() < 4) |
| return 0; |
| |
| // Try to turn linear trees of multiplies without other uses of the |
| // intermediate stages into minimal multiply DAGs with perfect sub-expression |
| // re-use. |
| SmallVector<Factor, 4> Factors; |
| if (!collectMultiplyFactors(Ops, Factors)) |
| return 0; // All distinct factors, so nothing left for us to do. |
| |
| IRBuilder<> Builder(I); |
| Value *V = buildMinimalMultiplyDAG(Builder, Factors); |
| if (Ops.empty()) |
| return V; |
| |
| ValueEntry NewEntry = ValueEntry(getRank(V), V); |
| Ops.insert(std::lower_bound(Ops.begin(), Ops.end(), NewEntry), NewEntry); |
| return 0; |
| } |
| |
| Value *Reassociate::OptimizeExpression(BinaryOperator *I, |
| SmallVectorImpl<ValueEntry> &Ops) { |
| // Now that we have the linearized expression tree, try to optimize it. |
| // Start by folding any constants that we found. |
| if (Ops.size() == 1) return Ops[0].Op; |
| |
| unsigned Opcode = I->getOpcode(); |
| |
| if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op)) |
| if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) { |
| Ops.pop_back(); |
| Ops.back().Op = ConstantExpr::get(Opcode, V1, V2); |
| return OptimizeExpression(I, Ops); |
| } |
| |
| // Check for destructive annihilation due to a constant being used. |
| if (ConstantInt *CstVal = dyn_cast<ConstantInt>(Ops.back().Op)) |
| switch (Opcode) { |
| default: break; |
| case Instruction::And: |
| if (CstVal->isZero()) // X & 0 -> 0 |
| return CstVal; |
| if (CstVal->isAllOnesValue()) // X & -1 -> X |
| Ops.pop_back(); |
| break; |
| case Instruction::Mul: |
| if (CstVal->isZero()) { // X * 0 -> 0 |
| ++NumAnnihil; |
| return CstVal; |
| } |
| |
| if (cast<ConstantInt>(CstVal)->isOne()) |
| Ops.pop_back(); // X * 1 -> X |
| break; |
| case Instruction::Or: |
| if (CstVal->isAllOnesValue()) // X | -1 -> -1 |
| return CstVal; |
| // FALLTHROUGH! |
| case Instruction::Add: |
| case Instruction::Xor: |
| if (CstVal->isZero()) // X [|^+] 0 -> X |
| Ops.pop_back(); |
| break; |
| } |
| if (Ops.size() == 1) return Ops[0].Op; |
| |
| // Handle destructive annihilation due to identities between elements in the |
| // argument list here. |
| unsigned NumOps = Ops.size(); |
| switch (Opcode) { |
| default: break; |
| case Instruction::And: |
| case Instruction::Or: |
| case Instruction::Xor: |
| if (Value *Result = OptimizeAndOrXor(Opcode, Ops)) |
| return Result; |
| break; |
| |
| case Instruction::Add: |
| if (Value *Result = OptimizeAdd(I, Ops)) |
| return Result; |
| break; |
| |
| case Instruction::Mul: |
| if (Value *Result = OptimizeMul(I, Ops)) |
| return Result; |
| break; |
| } |
| |
| if (Ops.size() != NumOps) |
| return OptimizeExpression(I, Ops); |
| return 0; |
| } |
| |
| /// EraseInst - Zap the given instruction, adding interesting operands to the |
| /// work list. |
| void Reassociate::EraseInst(Instruction *I) { |
| assert(isInstructionTriviallyDead(I) && "Trivially dead instructions only!"); |
| SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end()); |
| // Erase the dead instruction. |
| ValueRankMap.erase(I); |
| I->eraseFromParent(); |
| // Optimize its operands. |
| for (unsigned i = 0, e = Ops.size(); i != e; ++i) |
| if (Instruction *Op = dyn_cast<Instruction>(Ops[i])) { |
| // If this is a node in an expression tree, climb to the expression root |
| // and add that since that's where optimization actually happens. |
| unsigned Opcode = Op->getOpcode(); |
| while (Op->hasOneUse() && Op->use_back()->getOpcode() == Opcode) |
| Op = Op->use_back(); |
| RedoInsts.insert(Op); |
| } |
| } |
| |
| /// OptimizeInst - Inspect and optimize the given instruction. Note that erasing |
| /// instructions is not allowed. |
| void Reassociate::OptimizeInst(Instruction *I) { |
| // Only consider operations that we understand. |
| if (!isa<BinaryOperator>(I)) |
| return; |
| |
| if (I->getOpcode() == Instruction::Shl && |
| isa<ConstantInt>(I->getOperand(1))) |
| // If an operand of this shift is a reassociable multiply, or if the shift |
| // is used by a reassociable multiply or add, turn into a multiply. |
| if (isReassociableOp(I->getOperand(0), Instruction::Mul) || |
| (I->hasOneUse() && |
| (isReassociableOp(I->use_back(), Instruction::Mul) || |
| isReassociableOp(I->use_back(), Instruction::Add)))) { |
| Instruction *NI = ConvertShiftToMul(I); |
| RedoInsts.insert(I); |
| MadeChange = true; |
| I = NI; |
| } |
| |
| // Floating point binary operators are not associative, but we can still |
| // commute (some) of them, to canonicalize the order of their operands. |
| // This can potentially expose more CSE opportunities, and makes writing |
| // other transformations simpler. |
| if ((I->getType()->isFloatingPointTy() || I->getType()->isVectorTy())) { |
| // FAdd and FMul can be commuted. |
| if (I->getOpcode() != Instruction::FMul && |
| I->getOpcode() != Instruction::FAdd) |
| return; |
| |
| Value *LHS = I->getOperand(0); |
| Value *RHS = I->getOperand(1); |
| unsigned LHSRank = getRank(LHS); |
| unsigned RHSRank = getRank(RHS); |
| |
| // Sort the operands by rank. |
| if (RHSRank < LHSRank) { |
| I->setOperand(0, RHS); |
| I->setOperand(1, LHS); |
| } |
| |
| return; |
| } |
| |
| // Do not reassociate boolean (i1) expressions. We want to preserve the |
| // original order of evaluation for short-circuited comparisons that |
| // SimplifyCFG has folded to AND/OR expressions. If the expression |
| // is not further optimized, it is likely to be transformed back to a |
| // short-circuited form for code gen, and the source order may have been |
| // optimized for the most likely conditions. |
| if (I->getType()->isIntegerTy(1)) |
| return; |
| |
| // If this is a subtract instruction which is not already in negate form, |
| // see if we can convert it to X+-Y. |
| if (I->getOpcode() == Instruction::Sub) { |
| if (ShouldBreakUpSubtract(I)) { |
| Instruction *NI = BreakUpSubtract(I); |
| RedoInsts.insert(I); |
| MadeChange = true; |
| I = NI; |
| } else if (BinaryOperator::isNeg(I)) { |
| // Otherwise, this is a negation. See if the operand is a multiply tree |
| // and if this is not an inner node of a multiply tree. |
| if (isReassociableOp(I->getOperand(1), Instruction::Mul) && |
| (!I->hasOneUse() || |
| !isReassociableOp(I->use_back(), Instruction::Mul))) { |
| Instruction *NI = LowerNegateToMultiply(I); |
| RedoInsts.insert(I); |
| MadeChange = true; |
| I = NI; |
| } |
| } |
| } |
| |
| // If this instruction is an associative binary operator, process it. |
| if (!I->isAssociative()) return; |
| BinaryOperator *BO = cast<BinaryOperator>(I); |
| |
| // If this is an interior node of a reassociable tree, ignore it until we |
| // get to the root of the tree, to avoid N^2 analysis. |
| if (BO->hasOneUse() && BO->use_back()->getOpcode() == BO->getOpcode()) |
| return; |
| |
| // If this is an add tree that is used by a sub instruction, ignore it |
| // until we process the subtract. |
| if (BO->hasOneUse() && BO->getOpcode() == Instruction::Add && |
| cast<Instruction>(BO->use_back())->getOpcode() == Instruction::Sub) |
| return; |
| |
| ReassociateExpression(BO); |
| } |
| |
| Value *Reassociate::ReassociateExpression(BinaryOperator *I) { |
| |
| // First, walk the expression tree, linearizing the tree, collecting the |
| // operand information. |
| SmallVector<RepeatedValue, 8> Tree; |
| MadeChange |= LinearizeExprTree(I, Tree); |
| SmallVector<ValueEntry, 8> Ops; |
| Ops.reserve(Tree.size()); |
| for (unsigned i = 0, e = Tree.size(); i != e; ++i) { |
| RepeatedValue E = Tree[i]; |
| Ops.append(E.second.getZExtValue(), |
| ValueEntry(getRank(E.first), E.first)); |
| } |
| |
| DEBUG(dbgs() << "RAIn:\t"; PrintOps(I, Ops); dbgs() << '\n'); |
| |
| // Now that we have linearized the tree to a list and have gathered all of |
| // the operands and their ranks, sort the operands by their rank. Use a |
| // stable_sort so that values with equal ranks will have their relative |
| // positions maintained (and so the compiler is deterministic). Note that |
| // this sorts so that the highest ranking values end up at the beginning of |
| // the vector. |
| std::stable_sort(Ops.begin(), Ops.end()); |
| |
| // OptimizeExpression - Now that we have the expression tree in a convenient |
| // sorted form, optimize it globally if possible. |
| if (Value *V = OptimizeExpression(I, Ops)) { |
| // This expression tree simplified to something that isn't a tree, |
| // eliminate it. |
| DEBUG(dbgs() << "Reassoc to scalar: " << *V << '\n'); |
| I->replaceAllUsesWith(V); |
| if (Instruction *VI = dyn_cast<Instruction>(V)) |
| VI->setDebugLoc(I->getDebugLoc()); |
| RedoInsts.insert(I); |
| ++NumAnnihil; |
| return V; |
| } |
| |
| // We want to sink immediates as deeply as possible except in the case where |
| // this is a multiply tree used only by an add, and the immediate is a -1. |
| // In this case we reassociate to put the negation on the outside so that we |
| // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y |
| if (I->getOpcode() == Instruction::Mul && I->hasOneUse() && |
| cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add && |
| isa<ConstantInt>(Ops.back().Op) && |
| cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) { |
| ValueEntry Tmp = Ops.pop_back_val(); |
| Ops.insert(Ops.begin(), Tmp); |
| } |
| |
| DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n'); |
| |
| if (Ops.size() == 1) { |
| // This expression tree simplified to something that isn't a tree, |
| // eliminate it. |
| I->replaceAllUsesWith(Ops[0].Op); |
| if (Instruction *OI = dyn_cast<Instruction>(Ops[0].Op)) |
| OI->setDebugLoc(I->getDebugLoc()); |
| RedoInsts.insert(I); |
| return Ops[0].Op; |
| } |
| |
| // Now that we ordered and optimized the expressions, splat them back into |
| // the expression tree, removing any unneeded nodes. |
| RewriteExprTree(I, Ops); |
| return I; |
| } |
| |
| bool Reassociate::runOnFunction(Function &F) { |
| // Calculate the rank map for F |
| BuildRankMap(F); |
| |
| MadeChange = false; |
| for (Function::iterator BI = F.begin(), BE = F.end(); BI != BE; ++BI) { |
| // Optimize every instruction in the basic block. |
| for (BasicBlock::iterator II = BI->begin(), IE = BI->end(); II != IE; ) |
| if (isInstructionTriviallyDead(II)) { |
| EraseInst(II++); |
| } else { |
| OptimizeInst(II); |
| assert(II->getParent() == BI && "Moved to a different block!"); |
| ++II; |
| } |
| |
| // If this produced extra instructions to optimize, handle them now. |
| while (!RedoInsts.empty()) { |
| Instruction *I = RedoInsts.pop_back_val(); |
| if (isInstructionTriviallyDead(I)) |
| EraseInst(I); |
| else |
| OptimizeInst(I); |
| } |
| } |
| |
| // We are done with the rank map. |
| RankMap.clear(); |
| ValueRankMap.clear(); |
| |
| return MadeChange; |
| } |