X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=blobdiff_plain;f=lib%2FTransforms%2FScalar%2FReassociate.cpp;h=de1a3babdd56226d1465609b6bcf34d5459e73b4;hp=befdcfec774927e96a57142c303ac1b3a82458e8;hb=7cbd8a3e92221437048b484d5ef9c0a22d0f8c58;hpb=ed1f7c81aa24fd8126496a75c13c01db111b43ad diff --git a/lib/Transforms/Scalar/Reassociate.cpp b/lib/Transforms/Scalar/Reassociate.cpp index befdcfec774..de1a3babdd5 100644 --- a/lib/Transforms/Scalar/Reassociate.cpp +++ b/lib/Transforms/Scalar/Reassociate.cpp @@ -1,10 +1,10 @@ //===- Reassociate.cpp - Reassociate binary expressions -------------------===// -// +// // The LLVM Compiler Infrastructure // -// This file was developed by the LLVM research group and is distributed under -// the University of Illinois Open Source License. See LICENSE.TXT for details. -// +// 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 @@ -12,9 +12,6 @@ // // For example: 4 + (x + 5) -> x + (4 + 5) // -// Note that this pass works best if left shifts have been promoted to explicit -// multiplies before this pass executes. -// // 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 @@ -23,26 +20,59 @@ // //===----------------------------------------------------------------------===// +#define DEBUG_TYPE "reassociate" #include "llvm/Transforms/Scalar.h" +#include "llvm/Constants.h" +#include "llvm/DerivedTypes.h" #include "llvm/Function.h" -#include "llvm/iOperators.h" -#include "llvm/Type.h" +#include "llvm/Instructions.h" #include "llvm/Pass.h" -#include "llvm/Constant.h" +#include "llvm/Assembly/Writer.h" #include "llvm/Support/CFG.h" -#include "Support/Debug.h" -#include "Support/PostOrderIterator.h" -#include "Support/Statistic.h" +#include "llvm/Support/Compiler.h" +#include "llvm/Support/Debug.h" +#include "llvm/ADT/PostOrderIterator.h" +#include "llvm/ADT/Statistic.h" +#include +#include +using namespace llvm; + +STATISTIC(NumLinear , "Number of insts linearized"); +STATISTIC(NumChanged, "Number of insts reassociated"); +STATISTIC(NumAnnihil, "Number of expr tree annihilated"); +STATISTIC(NumFactor , "Number of multiplies factored"); namespace { - Statistic<> NumLinear ("reassociate","Number of insts linearized"); - Statistic<> NumChanged("reassociate","Number of insts reassociated"); - Statistic<> NumSwapped("reassociate","Number of insts with operands swapped"); + struct VISIBILITY_HIDDEN 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. + } +} - class Reassociate : public FunctionPass { +/// PrintOps - Print out the expression identified in the Ops list. +/// +static void PrintOps(Instruction *I, const std::vector &Ops) { + Module *M = I->getParent()->getParent()->getParent(); + cerr << Instruction::getOpcodeName(I->getOpcode()) << " " + << *Ops[0].Op->getType(); + for (unsigned i = 0, e = Ops.size(); i != e; ++i) + WriteAsOperand(*cerr.stream() << " ", Ops[i].Op, false, M) + << "," << Ops[i].Rank; +} + +namespace { + class VISIBILITY_HIDDEN Reassociate : public FunctionPass { std::map RankMap; std::map ValueRankMap; + bool MadeChange; public: + static char ID; // Pass identification, replacement for typeid + Reassociate() : FunctionPass((intptr_t)&ID) {} + bool runOnFunction(Function &F); virtual void getAnalysisUsage(AnalysisUsage &AU) const { @@ -51,129 +81,286 @@ namespace { private: void BuildRankMap(Function &F); unsigned getRank(Value *V); - bool ReassociateExpr(BinaryOperator *I); - bool ReassociateBB(BasicBlock *BB); + void ReassociateExpression(BinaryOperator *I); + void RewriteExprTree(BinaryOperator *I, std::vector &Ops, + unsigned Idx = 0); + Value *OptimizeExpression(BinaryOperator *I, std::vector &Ops); + void LinearizeExprTree(BinaryOperator *I, std::vector &Ops); + void LinearizeExpr(BinaryOperator *I); + Value *RemoveFactorFromExpression(Value *V, Value *Factor); + void ReassociateBB(BasicBlock *BB); + + void RemoveDeadBinaryOp(Value *V); }; +} + +char Reassociate::ID = 0; +static RegisterPass X("reassociate", "Reassociate expressions"); + +// Public interface to the Reassociate pass +FunctionPass *llvm::createReassociatePass() { return new Reassociate(); } - RegisterOpt X("reassociate", "Reassociate expressions"); +void Reassociate::RemoveDeadBinaryOp(Value *V) { + Instruction *Op = dyn_cast(V); + if (!Op || !isa(Op) || !isa(Op) || !Op->use_empty()) + return; + + Value *LHS = Op->getOperand(0), *RHS = Op->getOperand(1); + RemoveDeadBinaryOp(LHS); + RemoveDeadBinaryOp(RHS); } -FunctionPass *createReassociatePass() { return new Reassociate(); } + +static bool isUnmovableInstruction(Instruction *I) { + if (I->getOpcode() == Instruction::PHI || + I->getOpcode() == Instruction::Alloca || + I->getOpcode() == Instruction::Load || + I->getOpcode() == Instruction::Malloc || + I->getOpcode() == Instruction::Invoke || + I->getOpcode() == Instruction::Call || + 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::aiterator I = F.abegin(), E = F.aend(); I != E; ++I) + for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I) ValueRankMap[I] = ++i; ReversePostOrderTraversal RPOT(&F); for (ReversePostOrderTraversal::rpo_iterator I = RPOT.begin(), - E = RPOT.end(); I != E; ++I) - RankMap[*I] = ++i << 16; + 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) { if (isa(V)) return ValueRankMap[V]; // Function argument... - if (Instruction *I = dyn_cast(V)) { - // 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. - // - if (I->getOpcode() == Instruction::PHI || - I->getOpcode() == Instruction::Alloca || - I->getOpcode() == Instruction::Malloc || isa(I) || - I->mayWriteToMemory()) // Cannot move inst if it writes to memory! - return RankMap[I->getParent()]; - - unsigned &CachedRank = ValueRankMap[I]; - if (CachedRank) return CachedRank; // Rank already known? - - // If not, compute it! - 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))); - - DEBUG(std::cerr << "Calculated Rank[" << V->getName() << "] = " - << Rank+1 << "\n"); - - return CachedRank = Rank+1; - } + Instruction *I = dyn_cast(V); + if (I == 0) return 0; // Otherwise it's a global or constant, rank 0. + + unsigned &CachedRank = ValueRankMap[I]; + if (CachedRank) return CachedRank; // 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()->isInteger() || + (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I))) + ++Rank; - // Otherwise it's a global or constant, rank 0. + //DOUT << "Calculated Rank[" << V->getName() << "] = " + // << Rank << "\n"; + + return CachedRank = Rank; +} + +/// 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() || V->use_empty()) && isa(V) && + cast(V)->getOpcode() == Opcode) + return cast(V); return 0; } +/// LowerNegateToMultiply - Replace 0-X with X*-1. +/// +static Instruction *LowerNegateToMultiply(Instruction *Neg) { + Constant *Cst = ConstantInt::getAllOnesValue(Neg->getType()); -bool Reassociate::ReassociateExpr(BinaryOperator *I) { - Value *LHS = I->getOperand(0); - Value *RHS = I->getOperand(1); - unsigned LHSRank = getRank(LHS); - unsigned RHSRank = getRank(RHS); - - bool Changed = false; - - // Make sure the LHS of the operand always has the greater rank... - if (LHSRank < RHSRank) { - bool Success = !I->swapOperands(); - assert(Success && "swapOperands failed"); - - std::swap(LHS, RHS); - std::swap(LHSRank, RHSRank); - Changed = true; - ++NumSwapped; - DEBUG(std::cerr << "Transposed: " << I - /* << " Result BB: " << I->getParent()*/); + Instruction *Res = BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg); + Res->takeName(Neg); + Neg->replaceAllUsesWith(Res); + Neg->eraseFromParent(); + return Res; +} + +// Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'. +// Note that if D is also part of the expression tree that we recurse to +// linearize it as well. Besides that case, this does not recurse into A,B, or +// C. +void Reassociate::LinearizeExpr(BinaryOperator *I) { + BinaryOperator *LHS = cast(I->getOperand(0)); + BinaryOperator *RHS = cast(I->getOperand(1)); + assert(isReassociableOp(LHS, I->getOpcode()) && + isReassociableOp(RHS, I->getOpcode()) && + "Not an expression that needs linearization?"); + + DOUT << "Linear" << *LHS << *RHS << *I; + + // Move the RHS instruction to live immediately before I, avoiding breaking + // dominator properties. + RHS->moveBefore(I); + + // Move operands around to do the linearization. + I->setOperand(1, RHS->getOperand(0)); + RHS->setOperand(0, LHS); + I->setOperand(0, RHS); + + ++NumLinear; + MadeChange = true; + DOUT << "Linearized: " << *I; + + // If D is part of this expression tree, tail recurse. + if (isReassociableOp(I->getOperand(1), I->getOpcode())) + LinearizeExpr(I); +} + + +/// LinearizeExprTree - Given an associative binary expression tree, traverse +/// all of the uses putting it into canonical form. This forces a left-linear +/// form of the the expression (((a+b)+c)+d), and collects information about the +/// rank of the non-tree operands. +/// +/// NOTE: These intentionally destroys the expression tree operands (turning +/// them into undef values) to reduce #uses of the values. This means that the +/// caller MUST use something like RewriteExprTree to put the values back in. +/// +void Reassociate::LinearizeExprTree(BinaryOperator *I, + std::vector &Ops) { + Value *LHS = I->getOperand(0), *RHS = I->getOperand(1); + unsigned Opcode = I->getOpcode(); + + // First step, linearize the expression if it is in ((A+B)+(C+D)) form. + BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode); + BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode); + + // If this is a multiply expression tree and it contains internal negations, + // transform them into multiplies by -1 so they can be reassociated. + if (I->getOpcode() == Instruction::Mul) { + if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) { + LHS = LowerNegateToMultiply(cast(LHS)); + LHSBO = isReassociableOp(LHS, Opcode); + } + if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) { + RHS = LowerNegateToMultiply(cast(RHS)); + RHSBO = isReassociableOp(RHS, Opcode); + } } - - // If the LHS is the same operator as the current one is, and if we are the - // only expression using it... - // - if (BinaryOperator *LHSI = dyn_cast(LHS)) - if (LHSI->getOpcode() == I->getOpcode() && LHSI->hasOneUse()) { - // If the rank of our current RHS is less than the rank of the LHS's LHS, - // then we reassociate the two instructions... - - unsigned TakeOp = 0; - if (BinaryOperator *IOp = dyn_cast(LHSI->getOperand(0))) - if (IOp->getOpcode() == LHSI->getOpcode()) - TakeOp = 1; // Hoist out non-tree portion - - if (RHSRank < getRank(LHSI->getOperand(TakeOp))) { - // Convert ((a + 12) + 10) into (a + (12 + 10)) - I->setOperand(0, LHSI->getOperand(TakeOp)); - LHSI->setOperand(TakeOp, RHS); - I->setOperand(1, LHSI); - - // Move the LHS expression forward, to ensure that it is dominated by - // its operands. - LHSI->getParent()->getInstList().remove(LHSI); - I->getParent()->getInstList().insert(I, LHSI); - - ++NumChanged; - DEBUG(std::cerr << "Reassociated: " << I/* << " Result BB: " - << I->getParent()*/); - - // Since we modified the RHS instruction, make sure that we recheck it. - ReassociateExpr(LHSI); - ReassociateExpr(I); - return true; - } + + if (!LHSBO) { + if (!RHSBO) { + // Neither the LHS or RHS as part of the tree, thus this is a leaf. As + // such, just remember these operands and their rank. + Ops.push_back(ValueEntry(getRank(LHS), LHS)); + Ops.push_back(ValueEntry(getRank(RHS), RHS)); + + // Clear the leaves out. + I->setOperand(0, UndefValue::get(I->getType())); + I->setOperand(1, UndefValue::get(I->getType())); + return; + } else { + // Turn X+(Y+Z) -> (Y+Z)+X + std::swap(LHSBO, RHSBO); + std::swap(LHS, RHS); + bool Success = !I->swapOperands(); + assert(Success && "swapOperands failed"); + MadeChange = true; } + } else if (RHSBO) { + // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the the RHS is not + // part of the expression tree. + LinearizeExpr(I); + LHS = LHSBO = cast(I->getOperand(0)); + RHS = I->getOperand(1); + RHSBO = 0; + } - return Changed; + // Okay, now we know that the LHS is a nested expression and that the RHS is + // not. Perform reassociation. + assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!"); + + // Move LHS right before I to make sure that the tree expression dominates all + // values. + LHSBO->moveBefore(I); + + // Linearize the expression tree on the LHS. + LinearizeExprTree(LHSBO, Ops); + + // Remember the RHS operand and its rank. + Ops.push_back(ValueEntry(getRank(RHS), RHS)); + + // Clear the RHS leaf out. + I->setOperand(1, UndefValue::get(I->getType())); +} + +// RewriteExprTree - Now that the operands for this expression tree are +// linearized and optimized, emit them in-order. This function is written to be +// tail recursive. +void Reassociate::RewriteExprTree(BinaryOperator *I, + std::vector &Ops, + unsigned i) { + if (i+2 == Ops.size()) { + if (I->getOperand(0) != Ops[i].Op || + I->getOperand(1) != Ops[i+1].Op) { + Value *OldLHS = I->getOperand(0); + DOUT << "RA: " << *I; + I->setOperand(0, Ops[i].Op); + I->setOperand(1, Ops[i+1].Op); + DOUT << "TO: " << *I; + MadeChange = true; + ++NumChanged; + + // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3) + // delete the extra, now dead, nodes. + RemoveDeadBinaryOp(OldLHS); + } + return; + } + assert(i+2 < Ops.size() && "Ops index out of range!"); + + if (I->getOperand(1) != Ops[i].Op) { + DOUT << "RA: " << *I; + I->setOperand(1, Ops[i].Op); + DOUT << "TO: " << *I; + MadeChange = true; + ++NumChanged; + } + + BinaryOperator *LHS = cast(I->getOperand(0)); + assert(LHS->getOpcode() == I->getOpcode() && + "Improper expression tree!"); + + // Compactify the tree instructions together with each other to guarantee + // that the expression tree is dominated by all of Ops. + LHS->moveBefore(I); + RewriteExprTree(LHS, Ops, i+1); } + // 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, BasicBlock::iterator &BI) { +static Value *NegateValue(Value *V, Instruction *BI) { // 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, @@ -185,96 +372,498 @@ static Value *NegateValue(Value *V, BasicBlock::iterator &BI) { // if (Instruction *I = dyn_cast(V)) if (I->getOpcode() == Instruction::Add && I->hasOneUse()) { - Value *RHS = NegateValue(I->getOperand(1), BI); - Value *LHS = NegateValue(I->getOperand(0), BI); - - // We must actually insert a new add instruction here, because the neg - // instructions do not dominate the old add instruction in general. By - // adding it now, we are assured that the neg instructions we just - // inserted dominate the instruction we are about to insert after them. + // 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. // - return BinaryOperator::create(Instruction::Add, LHS, RHS, - I->getName()+".neg", - cast(RHS)->getNext()); + I->moveBefore(BI); + I->setName(I->getName()+".neg"); + return I; } // Insert a 'neg' instruction that subtracts the value from zero to get the // negation. // - return BI = BinaryOperator::createNeg(V, V->getName() + ".neg", BI); + 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; +} -bool Reassociate::ReassociateBB(BasicBlock *BB) { - bool Changed = false; - for (BasicBlock::iterator BI = BB->begin(); BI != BB->end(); ++BI) { +/// 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 Instruction *BreakUpSubtract(Instruction *Sub) { + // Convert a subtract into an add and a neg instruction... so that sub + // instructions can 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); + Instruction *New = + BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub); + New->takeName(Sub); - DEBUG(std::cerr << "Processing: " << *BI); - if (BI->getOpcode() == Instruction::Sub && !BinaryOperator::isNeg(BI)) { - // Convert a subtract into an add and a neg instruction... so that sub - // instructions can 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... - // - std::string Name = BI->getName(); - BI->setName(""); - Instruction *New = - BinaryOperator::create(Instruction::Add, BI->getOperand(0), - BI->getOperand(1), Name, BI); + // Everyone now refers to the add instruction. + Sub->replaceAllUsesWith(New); + Sub->eraseFromParent(); - // Everyone now refers to the add instruction... - BI->replaceAllUsesWith(New); + DOUT << "Negated: " << *New; + 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 Instruction *ConvertShiftToMul(Instruction *Shl) { + // 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(Shl->getOperand(0), Instruction::Mul) || + (Shl->hasOneUse() && + (isReassociableOp(Shl->use_back(), Instruction::Mul) || + isReassociableOp(Shl->use_back(), Instruction::Add)))) { + Constant *MulCst = ConstantInt::get(Shl->getType(), 1); + MulCst = ConstantExpr::getShl(MulCst, cast(Shl->getOperand(1))); + + Instruction *Mul = BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, + "", Shl); + Mul->takeName(Shl); + Shl->replaceAllUsesWith(Mul); + Shl->eraseFromParent(); + return Mul; + } + return 0; +} - // Put the new add in the place of the subtract... deleting the subtract - BB->getInstList().erase(BI); +// 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. +static unsigned FindInOperandList(std::vector &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; +} - BI = New; - New->setOperand(1, NegateValue(New->getOperand(1), BI)); - - Changed = true; - DEBUG(std::cerr << "Negated: " << New /*<< " Result BB: " << BB*/); +/// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together +/// and returning the result. Insert the tree before I. +static Value *EmitAddTreeOfValues(Instruction *I, std::vector &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; + + std::vector Factors; + LinearizeExprTree(BO, Factors); + + bool FoundFactor = 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 (!FoundFactor) { + // Make sure to restore the operands to the expression tree. + RewriteExprTree(BO, Factors); + return 0; + } + + if (Factors.size() == 1) return Factors[0].Op; + + RewriteExprTree(BO, Factors); + return BO; +} + +/// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively +/// add its operands as factors, otherwise add V to the list of factors. +static void FindSingleUseMultiplyFactors(Value *V, + std::vector &Factors) { + BinaryOperator *BO; + if ((!V->hasOneUse() && !V->use_empty()) || + !(BO = dyn_cast(V)) || + BO->getOpcode() != Instruction::Mul) { + Factors.push_back(V); + return; + } + + // Otherwise, add the LHS and RHS to the list of factors. + FindSingleUseMultiplyFactors(BO->getOperand(1), Factors); + FindSingleUseMultiplyFactors(BO->getOperand(0), Factors); +} + + + +Value *Reassociate::OptimizeExpression(BinaryOperator *I, + std::vector &Ops) { + // Now that we have the linearized expression tree, try to optimize it. + // Start by folding any constants that we found. + bool IterateOptimization = false; + if (Ops.size() == 1) return Ops[0].Op; + + unsigned Opcode = I->getOpcode(); + + if (Constant *V1 = dyn_cast(Ops[Ops.size()-2].Op)) + if (Constant *V2 = dyn_cast(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(Ops.back().Op)) + switch (Opcode) { + default: break; + case Instruction::And: + if (CstVal->isZero()) { // ... & 0 -> 0 + ++NumAnnihil; + return CstVal; + } else if (CstVal->isAllOnesValue()) { // ... & -1 -> ... + Ops.pop_back(); + } + break; + case Instruction::Mul: + if (CstVal->isZero()) { // ... * 0 -> 0 + ++NumAnnihil; + return CstVal; + } else if (cast(CstVal)->isOne()) { + Ops.pop_back(); // ... * 1 -> ... + } + break; + case Instruction::Or: + if (CstVal->isAllOnesValue()) { // ... | -1 -> -1 + ++NumAnnihil; + return CstVal; + } + // FALLTHROUGH! + case Instruction::Add: + case Instruction::Xor: + if (CstVal->isZero()) // ... [|^+] 0 -> ... + Ops.pop_back(); + break; + } + if (Ops.size() == 1) return Ops[0].Op; + + // Handle destructive annihilation do to identities between elements in the + // argument list here. + switch (Opcode) { + default: break; + case Instruction::And: + case Instruction::Or: + case Instruction::Xor: + // 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 + ++NumAnnihil; + return Constant::getNullValue(X->getType()); + } else if (Opcode == Instruction::Or) { // ...|X|~X = -1 + ++NumAnnihil; + return ConstantInt::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. + Ops.erase(Ops.begin()+i); + --i; --e; + IterateOptimization = true; + ++NumAnnihil; + } else { + assert(Opcode == Instruction::Xor); + if (e == 2) { + ++NumAnnihil; + return Constant::getNullValue(Ops[0].Op->getType()); + } + // ... X^X -> ... + Ops.erase(Ops.begin()+i, Ops.begin()+i+2); + i -= 1; e -= 2; + IterateOptimization = true; + ++NumAnnihil; + } + } + } + break; + + case Instruction::Add: + // Scan the operand lists looking for X and -X pairs. If we find any, we + // can simplify the expression. X+-X == 0. + for (unsigned i = 0, e = Ops.size(); i != e; ++i) { + assert(i < Ops.size()); + // Check for X and -X in the operand list. + if (BinaryOperator::isNeg(Ops[i].Op)) { + Value *X = BinaryOperator::getNegArgument(Ops[i].Op); + unsigned FoundX = FindInOperandList(Ops, i, X); + if (FoundX != i) { + // Remove X and -X from the operand list. + if (Ops.size() == 2) { + ++NumAnnihil; + return Constant::getNullValue(X->getType()); + } else { + Ops.erase(Ops.begin()+i); + if (i < FoundX) + --FoundX; + else + --i; // Need to back up an extra one. + Ops.erase(Ops.begin()+FoundX); + IterateOptimization = true; + ++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. + std::map FactorOccurrences; + unsigned MaxOcc = 0; + Value *MaxOccVal = 0; + for (unsigned i = 0, e = Ops.size(); i != e; ++i) { + if (BinaryOperator *BOp = dyn_cast(Ops[i].Op)) { + if (BOp->getOpcode() == Instruction::Mul && BOp->use_empty()) { + // Compute all of the factors of this added value. + std::vector Factors; + FindSingleUseMultiplyFactors(BOp, Factors); + assert(Factors.size() > 1 && "Bad linearize!"); + + // Add one to FactorOccurrences for each unique factor in this op. + if (Factors.size() == 2) { + unsigned Occ = ++FactorOccurrences[Factors[0]]; + if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[0]; } + if (Factors[0] != Factors[1]) { // Don't double count A*A. + Occ = ++FactorOccurrences[Factors[1]]; + if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[1]; } + } + } else { + std::set Duplicates; + for (unsigned i = 0, e = Factors.size(); i != e; ++i) { + if (Duplicates.insert(Factors[i]).second) { + unsigned Occ = ++FactorOccurrences[Factors[i]]; + if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[i]; } + } + } + } + } + } } - // If this instruction is a commutative binary operator, and the ranks of - // the two operands are sorted incorrectly, fix it now. - // - if (BI->isAssociative()) { - BinaryOperator *I = cast(BI); - if (!I->use_empty()) { - // Make sure that we don't have a tree-shaped computation. If we do, - // linearize it. Convert (A+B)+(C+D) into ((A+B)+C)+D - // - Instruction *LHSI = dyn_cast(I->getOperand(0)); - Instruction *RHSI = dyn_cast(I->getOperand(1)); - if (LHSI && (int)LHSI->getOpcode() == I->getOpcode() && - RHSI && (int)RHSI->getOpcode() == I->getOpcode() && - RHSI->hasOneUse()) { - // Insert a new temporary instruction... (A+B)+C - BinaryOperator *Tmp = BinaryOperator::create(I->getOpcode(), LHSI, - RHSI->getOperand(0), - RHSI->getName()+".ra", - BI); - BI = Tmp; - I->setOperand(0, Tmp); - I->setOperand(1, RHSI->getOperand(1)); - - // Process the temporary instruction for reassociation now. - I = Tmp; - ++NumLinear; - Changed = true; - DEBUG(std::cerr << "Linearized: " << I/* << " Result BB: " << BB*/); + // If any factor occurred more than one time, we can pull it out. + if (MaxOcc > 1) { + DOUT << "\nFACTORING [" << MaxOcc << "]: " << *MaxOccVal << "\n"; + + // 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); + std::vector NewMulOps; + for (unsigned i = 0, e = Ops.size(); i != e; ++i) { + if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) { + NewMulOps.push_back(V); + Ops.erase(Ops.begin()+i); + --i; --e; } + } + + // No need for extra uses anymore. + delete DummyInst; + + unsigned NumAddedValues = NewMulOps.size(); + Value *V = EmitAddTreeOfValues(I, NewMulOps); + Value *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I); + + // Now that we have inserted V and its sole use, 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)) + if (NumAddedValues > 1) + ReassociateExpression(cast(V)); + + ++NumFactor; + + if (Ops.empty()) + return V2; - // Make sure that this expression is correctly reassociated with respect - // to it's used values... - // - Changed |= ReassociateExpr(I); + // Add the new value to the list of things being added. + Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2)); + + // Rewrite the tree so that there is now a use of V. + RewriteExprTree(I, Ops); + return OptimizeExpression(I, Ops); + } + break; + //case Instruction::Mul: + } + + if (IterateOptimization) + return OptimizeExpression(I, Ops); + return 0; +} + + +/// ReassociateBB - Inspect all of the instructions in this basic block, +/// reassociating them as we go. +void Reassociate::ReassociateBB(BasicBlock *BB) { + for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) { + Instruction *BI = BBI++; + if (BI->getOpcode() == Instruction::Shl && + isa(BI->getOperand(1))) + if (Instruction *NI = ConvertShiftToMul(BI)) { + MadeChange = true; + BI = NI; + } + + // Reject cases where it is pointless to do this. + if (!isa(BI) || BI->getType()->isFloatingPoint() || + isa(BI->getType())) + continue; // Floating point ops are not associative. + + // If this is a subtract instruction which is not already in negate form, + // see if we can convert it to X+-Y. + if (BI->getOpcode() == Instruction::Sub) { + if (ShouldBreakUpSubtract(BI)) { + BI = BreakUpSubtract(BI); + MadeChange = true; + } else if (BinaryOperator::isNeg(BI)) { + // 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(BI->getOperand(1), Instruction::Mul) && + (!BI->hasOneUse() || + !isReassociableOp(BI->use_back(), Instruction::Mul))) { + BI = LowerNegateToMultiply(BI); + MadeChange = true; + } } } + + // If this instruction is a commutative binary operator, process it. + if (!BI->isAssociative()) continue; + BinaryOperator *I = cast(BI); + + // 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 (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode())) + continue; + + // If this is an add tree that is used by a sub instruction, ignore it + // until we process the subtract. + if (I->hasOneUse() && I->getOpcode() == Instruction::Add && + cast(I->use_back())->getOpcode() == Instruction::Sub) + continue; + + ReassociateExpression(I); } +} - return Changed; +void Reassociate::ReassociateExpression(BinaryOperator *I) { + + // First, walk the expression tree, linearizing the tree, collecting + std::vector Ops; + LinearizeExprTree(I, Ops); + + DOUT << "RAIn:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\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. + DOUT << "Reassoc to scalar: " << *V << "\n"; + I->replaceAllUsesWith(V); + RemoveDeadBinaryOp(I); + return; + } + + // 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(I->use_back())->getOpcode() == Instruction::Add && + isa(Ops.back().Op) && + cast(Ops.back().Op)->isAllOnesValue()) { + Ops.insert(Ops.begin(), Ops.back()); + Ops.pop_back(); + } + + DOUT << "RAOut:\t"; DEBUG(PrintOps(I, Ops)); DOUT << "\n"; + + if (Ops.size() == 1) { + // This expression tree simplified to something that isn't a tree, + // eliminate it. + I->replaceAllUsesWith(Ops[0].Op); + RemoveDeadBinaryOp(I); + } else { + // Now that we ordered and optimized the expressions, splat them back into + // the expression tree, removing any unneeded nodes. + RewriteExprTree(I, Ops); + } } @@ -282,12 +871,13 @@ bool Reassociate::runOnFunction(Function &F) { // Recalculate the rank map for F BuildRankMap(F); - bool Changed = false; + MadeChange = false; for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) - Changed |= ReassociateBB(FI); + ReassociateBB(FI); // We are done with the rank map... RankMap.clear(); ValueRankMap.clear(); - return Changed; + return MadeChange; } +