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Diffstat (limited to 'contrib/llvm/lib/Transforms/Scalar/Reassociate.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Scalar/Reassociate.cpp | 1123 |
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diff --git a/contrib/llvm/lib/Transforms/Scalar/Reassociate.cpp b/contrib/llvm/lib/Transforms/Scalar/Reassociate.cpp new file mode 100644 index 000000000000..e6341ae3071f --- /dev/null +++ b/contrib/llvm/lib/Transforms/Scalar/Reassociate.cpp @@ -0,0 +1,1123 @@ +//===- 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/Debug.h" +#include "llvm/Support/ValueHandle.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/ADT/PostOrderIterator.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/ADT/DenseMap.h" +#include <algorithm> +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 { + 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 { + class Reassociate : public FunctionPass { + DenseMap<BasicBlock*, unsigned> RankMap; + DenseMap<AssertingVH<>, unsigned> ValueRankMap; + SmallVector<WeakVH, 8> RedoInsts; + SmallVector<WeakVH, 8> DeadInsts; + 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, + unsigned Idx = 0); + Value *OptimizeExpression(BinaryOperator *I, + SmallVectorImpl<ValueEntry> &Ops); + Value *OptimizeAdd(Instruction *I, SmallVectorImpl<ValueEntry> &Ops); + void LinearizeExprTree(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops); + void LinearizeExpr(BinaryOperator *I); + Value *RemoveFactorFromExpression(Value *V, Value *Factor); + void ReassociateInst(BasicBlock::iterator &BBI); + + void RemoveDeadBinaryOp(Value *V); + }; +} + +char Reassociate::ID = 0; +INITIALIZE_PASS(Reassociate, "reassociate", + "Reassociate expressions", false, false) + +// Public interface to the Reassociate pass +FunctionPass *llvm::createReassociatePass() { return new Reassociate(); } + +void Reassociate::RemoveDeadBinaryOp(Value *V) { + Instruction *Op = dyn_cast<Instruction>(V); + if (!Op || !isa<BinaryOperator>(Op)) + return; + + Value *LHS = Op->getOperand(0), *RHS = Op->getOperand(1); + + ValueRankMap.erase(Op); + DeadInsts.push_back(Op); + RemoveDeadBinaryOp(LHS); + RemoveDeadBinaryOp(RHS); +} + + +static bool isUnmovableInstruction(Instruction *I) { + if (I->getOpcode() == Instruction::PHI || + 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; +} + +/// 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<Instruction>(V) && + cast<Instruction>(V)->getOpcode() == Opcode) + return cast<BinaryOperator>(V); + return 0; +} + +/// LowerNegateToMultiply - Replace 0-X with X*-1. +/// +static Instruction *LowerNegateToMultiply(Instruction *Neg, + DenseMap<AssertingVH<>, unsigned> &ValueRankMap) { + Constant *Cst = Constant::getAllOnesValue(Neg->getType()); + + Instruction *Res = BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg); + ValueRankMap.erase(Neg); + Res->takeName(Neg); + Neg->replaceAllUsesWith(Res); + Res->setDebugLoc(Neg->getDebugLoc()); + 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<BinaryOperator>(I->getOperand(0)); + BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1)); + assert(isReassociableOp(LHS, I->getOpcode()) && + isReassociableOp(RHS, I->getOpcode()) && + "Not an expression that needs linearization?"); + + DEBUG(dbgs() << "Linear" << *LHS << '\n' << *RHS << '\n' << *I << '\n'); + + // 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); + + // Conservatively clear all the optional flags, which may not hold + // after the reassociation. + I->clearSubclassOptionalData(); + LHS->clearSubclassOptionalData(); + RHS->clearSubclassOptionalData(); + + ++NumLinear; + MadeChange = true; + DEBUG(dbgs() << "Linearized: " << *I << '\n'); + + // 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 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, + SmallVectorImpl<ValueEntry> &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<Instruction>(LHS), ValueRankMap); + LHSBO = isReassociableOp(LHS, Opcode); + } + if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) { + RHS = LowerNegateToMultiply(cast<Instruction>(RHS), ValueRankMap); + RHSBO = isReassociableOp(RHS, Opcode); + } + } + + 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; + } + + // Turn X+(Y+Z) -> (Y+Z)+X + std::swap(LHSBO, RHSBO); + std::swap(LHS, RHS); + bool Success = !I->swapOperands(); + assert(Success && "swapOperands failed"); + Success = false; + MadeChange = true; + } else if (RHSBO) { + // Turn (A+B)+(C+D) -> (((A+B)+C)+D). This guarantees the RHS is not + // part of the expression tree. + LinearizeExpr(I); + LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0)); + RHS = I->getOperand(1); + RHSBO = 0; + } + + // 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, + SmallVectorImpl<ValueEntry> &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); + DEBUG(dbgs() << "RA: " << *I << '\n'); + I->setOperand(0, Ops[i].Op); + I->setOperand(1, Ops[i+1].Op); + + // Clear all the optional flags, which may not hold after the + // reassociation if the expression involved more than just this operation. + if (Ops.size() != 2) + I->clearSubclassOptionalData(); + + DEBUG(dbgs() << "TO: " << *I << '\n'); + 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) { + DEBUG(dbgs() << "RA: " << *I << '\n'); + I->setOperand(1, Ops[i].Op); + + // Conservatively clear all the optional flags, which may not hold + // after the reassociation. + I->clearSubclassOptionalData(); + + DEBUG(dbgs() << "TO: " << *I << '\n'); + MadeChange = true; + ++NumChanged; + } + + BinaryOperator *LHS = cast<BinaryOperator>(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, 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 (Instruction *I = dyn_cast<Instruction>(V)) + if (I->getOpcode() == Instruction::Add && I->hasOneUse()) { + // 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 Instruction *BreakUpSubtract(Instruction *Sub, + DenseMap<AssertingVH<>, unsigned> &ValueRankMap) { + // 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); + Instruction *New = + BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub); + New->takeName(Sub); + + // Everyone now refers to the add instruction. + ValueRankMap.erase(Sub); + Sub->replaceAllUsesWith(New); + New->setDebugLoc(Sub->getDebugLoc()); + Sub->eraseFromParent(); + + 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 Instruction *ConvertShiftToMul(Instruction *Shl, + DenseMap<AssertingVH<>, unsigned> &ValueRankMap) { + // 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<Constant>(Shl->getOperand(1))); + + Instruction *Mul = + BinaryOperator::CreateMul(Shl->getOperand(0), MulCst, "", Shl); + ValueRankMap.erase(Shl); + Mul->takeName(Shl); + Shl->replaceAllUsesWith(Mul); + Mul->setDebugLoc(Shl->getDebugLoc()); + Shl->eraseFromParent(); + return Mul; + } + return 0; +} + +// 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<Value*> &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<ValueEntry, 8> Factors; + LinearizeExprTree(BO, Factors); + + 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) { + ValueRankMap.erase(BO); + DeadInsts.push_back(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, + bool IsRoot) { + BinaryOperator *BO; + if (!(V->hasOneUse() || V->use_empty()) || // More than one use. + !(BO = dyn_cast<BinaryOperator>(V)) || + BO->getOpcode() != Instruction::Mul) { + Factors.push_back(V); + return; + } + + // If this value has a single use because it is another input to the add + // tree we're reassociating and we dropped its use, it actually has two + // uses and we can't factor it. + if (!IsRoot) { + for (unsigned i = 0, e = Ops.size(); i != e; ++i) + if (Ops[i].Op == V) { + Factors.push_back(V); + return; + } + } + + + // Otherwise, add the LHS and RHS to the list of factors. + FindSingleUseMultiplyFactors(BO->getOperand(1), Factors, Ops, false); + FindSingleUseMultiplyFactors(BO->getOperand(0), Factors, Ops, false); +} + +/// 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.push_back(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 = dyn_cast<BinaryOperator>(Ops[i].Op); + if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty()) + continue; + + // Compute all of the factors of this added value. + SmallVector<Value*, 8> Factors; + FindSingleUseMultiplyFactors(BOp, Factors, Ops, true); + 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<Value*, 4> NewMulOps; + for (unsigned i = 0; i != Ops.size(); ++i) { + // Only try to remove factors from expressions we're allowed to. + BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op); + if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty()) + 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; + V = ReassociateExpression(cast<BinaryOperator>(V)); + + // Create the multiply. + Value *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. + V2 = ReassociateExpression(cast<BinaryOperator>(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; +} + +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. + bool IterateOptimization = false; + 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. + switch (Opcode) { + default: break; + case Instruction::And: + case Instruction::Or: + case Instruction::Xor: { + unsigned NumOps = Ops.size(); + if (Value *Result = OptimizeAndOrXor(Opcode, Ops)) + return Result; + IterateOptimization |= Ops.size() != NumOps; + break; + } + + case Instruction::Add: { + unsigned NumOps = Ops.size(); + if (Value *Result = OptimizeAdd(I, Ops)) + return Result; + IterateOptimization |= Ops.size() != NumOps; + } + + break; + //case Instruction::Mul: + } + + if (IterateOptimization) + return OptimizeExpression(I, Ops); + return 0; +} + + +/// ReassociateInst - Inspect and reassociate the instruction at the +/// given position, post-incrementing the position. +void Reassociate::ReassociateInst(BasicBlock::iterator &BBI) { + Instruction *BI = BBI++; + if (BI->getOpcode() == Instruction::Shl && + isa<ConstantInt>(BI->getOperand(1))) + if (Instruction *NI = ConvertShiftToMul(BI, ValueRankMap)) { + MadeChange = true; + BI = NI; + } + + // Reject cases where it is pointless to do this. + if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPointTy() || + BI->getType()->isVectorTy()) + return; // Floating point ops are not associative. + + // 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 (BI->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 (BI->getOpcode() == Instruction::Sub) { + if (ShouldBreakUpSubtract(BI)) { + BI = BreakUpSubtract(BI, ValueRankMap); + // Reset the BBI iterator in case BreakUpSubtract changed the + // instruction it points to. + BBI = BI; + ++BBI; + 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, ValueRankMap); + MadeChange = true; + } + } + } + + // If this instruction is a commutative binary operator, process it. + if (!BI->isAssociative()) return; + BinaryOperator *I = cast<BinaryOperator>(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())) + return; + + // 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<Instruction>(I->use_back())->getOpcode() == Instruction::Sub) + return; + + ReassociateExpression(I); +} + +Value *Reassociate::ReassociateExpression(BinaryOperator *I) { + + // First, walk the expression tree, linearizing the tree, collecting the + // operand information. + SmallVector<ValueEntry, 8> Ops; + LinearizeExprTree(I, Ops); + + 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()); + RemoveDeadBinaryOp(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()); + RemoveDeadBinaryOp(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) { + // Recalculate the rank map for F + BuildRankMap(F); + + MadeChange = false; + for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) + for (BasicBlock::iterator BBI = FI->begin(); BBI != FI->end(); ) + ReassociateInst(BBI); + + // Now that we're done, revisit any instructions which are likely to + // have secondary reassociation opportunities. + while (!RedoInsts.empty()) + if (Value *V = RedoInsts.pop_back_val()) { + BasicBlock::iterator BBI = cast<Instruction>(V); + ReassociateInst(BBI); + } + + // Now that we're done, delete any instructions which are no longer used. + while (!DeadInsts.empty()) + if (Value *V = DeadInsts.pop_back_val()) + RecursivelyDeleteTriviallyDeadInstructions(V); + + // We are done with the rank map. + RankMap.clear(); + ValueRankMap.clear(); + return MadeChange; +} + |