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Reassociate.cpp

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00001 //===- Reassociate.cpp - Reassociate binary expressions -------------------===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file was developed by the LLVM research group and is distributed under
00006 // the University of Illinois Open Source License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This pass reassociates commutative expressions in an order that is designed
00011 // to promote better constant propagation, GCSE, LICM, PRE...
00012 //
00013 // For example: 4 + (x + 5) -> x + (4 + 5)
00014 //
00015 // In the implementation of this algorithm, constants are assigned rank = 0,
00016 // function arguments are rank = 1, and other values are assigned ranks
00017 // corresponding to the reverse post order traversal of current function
00018 // (starting at 2), which effectively gives values in deep loops higher rank
00019 // than values not in loops.
00020 //
00021 //===----------------------------------------------------------------------===//
00022 
00023 #define DEBUG_TYPE "reassociate"
00024 #include "llvm/Transforms/Scalar.h"
00025 #include "llvm/Constants.h"
00026 #include "llvm/Function.h"
00027 #include "llvm/Instructions.h"
00028 #include "llvm/Pass.h"
00029 #include "llvm/Type.h"
00030 #include "llvm/Assembly/Writer.h"
00031 #include "llvm/Support/CFG.h"
00032 #include "llvm/Support/Debug.h"
00033 #include "llvm/ADT/PostOrderIterator.h"
00034 #include "llvm/ADT/Statistic.h"
00035 #include <algorithm>
00036 #include <iostream>
00037 using namespace llvm;
00038 
00039 namespace {
00040   Statistic<> NumLinear ("reassociate","Number of insts linearized");
00041   Statistic<> NumChanged("reassociate","Number of insts reassociated");
00042   Statistic<> NumSwapped("reassociate","Number of insts with operands swapped");
00043   Statistic<> NumAnnihil("reassociate","Number of expr tree annihilated");
00044   Statistic<> NumFactor ("reassociate","Number of multiplies factored");
00045 
00046   struct ValueEntry {
00047     unsigned Rank;
00048     Value *Op;
00049     ValueEntry(unsigned R, Value *O) : Rank(R), Op(O) {}
00050   };
00051   inline bool operator<(const ValueEntry &LHS, const ValueEntry &RHS) {
00052     return LHS.Rank > RHS.Rank;   // Sort so that highest rank goes to start.
00053   }
00054 }
00055 
00056 /// PrintOps - Print out the expression identified in the Ops list.
00057 ///
00058 static void PrintOps(Instruction *I, const std::vector<ValueEntry> &Ops) {
00059   Module *M = I->getParent()->getParent()->getParent();
00060   std::cerr << Instruction::getOpcodeName(I->getOpcode()) << " "
00061   << *Ops[0].Op->getType();
00062   for (unsigned i = 0, e = Ops.size(); i != e; ++i)
00063     WriteAsOperand(std::cerr << " ", Ops[i].Op, false, true, M)
00064       << "," << Ops[i].Rank;
00065 }
00066   
00067 namespace {  
00068   class Reassociate : public FunctionPass {
00069     std::map<BasicBlock*, unsigned> RankMap;
00070     std::map<Value*, unsigned> ValueRankMap;
00071     bool MadeChange;
00072   public:
00073     bool runOnFunction(Function &F);
00074 
00075     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
00076       AU.setPreservesCFG();
00077     }
00078   private:
00079     void BuildRankMap(Function &F);
00080     unsigned getRank(Value *V);
00081     void ReassociateExpression(BinaryOperator *I);
00082     void RewriteExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops,
00083                          unsigned Idx = 0);
00084     Value *OptimizeExpression(BinaryOperator *I, std::vector<ValueEntry> &Ops);
00085     void LinearizeExprTree(BinaryOperator *I, std::vector<ValueEntry> &Ops);
00086     void LinearizeExpr(BinaryOperator *I);
00087     Value *RemoveFactorFromExpression(Value *V, Value *Factor);
00088     void ReassociateBB(BasicBlock *BB);
00089     
00090     void RemoveDeadBinaryOp(Value *V);
00091   };
00092 
00093   RegisterOpt<Reassociate> X("reassociate", "Reassociate expressions");
00094 }
00095 
00096 // Public interface to the Reassociate pass
00097 FunctionPass *llvm::createReassociatePass() { return new Reassociate(); }
00098 
00099 void Reassociate::RemoveDeadBinaryOp(Value *V) {
00100   BinaryOperator *BOp = dyn_cast<BinaryOperator>(V);
00101   if (!BOp || !BOp->use_empty()) return;
00102   
00103   Value *LHS = BOp->getOperand(0), *RHS = BOp->getOperand(1);
00104   RemoveDeadBinaryOp(LHS);
00105   RemoveDeadBinaryOp(RHS);
00106 }
00107 
00108 
00109 static bool isUnmovableInstruction(Instruction *I) {
00110   if (I->getOpcode() == Instruction::PHI ||
00111       I->getOpcode() == Instruction::Alloca ||
00112       I->getOpcode() == Instruction::Load ||
00113       I->getOpcode() == Instruction::Malloc ||
00114       I->getOpcode() == Instruction::Invoke ||
00115       I->getOpcode() == Instruction::Call ||
00116       I->getOpcode() == Instruction::Div ||
00117       I->getOpcode() == Instruction::Rem)
00118     return true;
00119   return false;
00120 }
00121 
00122 void Reassociate::BuildRankMap(Function &F) {
00123   unsigned i = 2;
00124 
00125   // Assign distinct ranks to function arguments
00126   for (Function::arg_iterator I = F.arg_begin(), E = F.arg_end(); I != E; ++I)
00127     ValueRankMap[I] = ++i;
00128 
00129   ReversePostOrderTraversal<Function*> RPOT(&F);
00130   for (ReversePostOrderTraversal<Function*>::rpo_iterator I = RPOT.begin(),
00131          E = RPOT.end(); I != E; ++I) {
00132     BasicBlock *BB = *I;
00133     unsigned BBRank = RankMap[BB] = ++i << 16;
00134 
00135     // Walk the basic block, adding precomputed ranks for any instructions that
00136     // we cannot move.  This ensures that the ranks for these instructions are
00137     // all different in the block.
00138     for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
00139       if (isUnmovableInstruction(I))
00140         ValueRankMap[I] = ++BBRank;
00141   }
00142 }
00143 
00144 unsigned Reassociate::getRank(Value *V) {
00145   if (isa<Argument>(V)) return ValueRankMap[V];   // Function argument...
00146 
00147   Instruction *I = dyn_cast<Instruction>(V);
00148   if (I == 0) return 0;  // Otherwise it's a global or constant, rank 0.
00149 
00150   unsigned &CachedRank = ValueRankMap[I];
00151   if (CachedRank) return CachedRank;    // Rank already known?
00152 
00153   // If this is an expression, return the 1+MAX(rank(LHS), rank(RHS)) so that
00154   // we can reassociate expressions for code motion!  Since we do not recurse
00155   // for PHI nodes, we cannot have infinite recursion here, because there
00156   // cannot be loops in the value graph that do not go through PHI nodes.
00157   unsigned Rank = 0, MaxRank = RankMap[I->getParent()];
00158   for (unsigned i = 0, e = I->getNumOperands();
00159        i != e && Rank != MaxRank; ++i)
00160     Rank = std::max(Rank, getRank(I->getOperand(i)));
00161 
00162   // If this is a not or neg instruction, do not count it for rank.  This
00163   // assures us that X and ~X will have the same rank.
00164   if (!I->getType()->isIntegral() ||
00165       (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
00166     ++Rank;
00167 
00168   //DEBUG(std::cerr << "Calculated Rank[" << V->getName() << "] = "
00169   //<< Rank << "\n");
00170 
00171   return CachedRank = Rank;
00172 }
00173 
00174 /// isReassociableOp - Return true if V is an instruction of the specified
00175 /// opcode and if it only has one use.
00176 static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode) {
00177   if ((V->hasOneUse() || V->use_empty()) && isa<Instruction>(V) &&
00178       cast<Instruction>(V)->getOpcode() == Opcode)
00179     return cast<BinaryOperator>(V);
00180   return 0;
00181 }
00182 
00183 /// LowerNegateToMultiply - Replace 0-X with X*-1.
00184 ///
00185 static Instruction *LowerNegateToMultiply(Instruction *Neg) {
00186   Constant *Cst;
00187   if (Neg->getType()->isFloatingPoint())
00188     Cst = ConstantFP::get(Neg->getType(), -1);
00189   else
00190     Cst = ConstantInt::getAllOnesValue(Neg->getType());
00191 
00192   std::string NegName = Neg->getName(); Neg->setName("");
00193   Instruction *Res = BinaryOperator::createMul(Neg->getOperand(1), Cst, NegName,
00194                                                Neg);
00195   Neg->replaceAllUsesWith(Res);
00196   Neg->eraseFromParent();
00197   return Res;
00198 }
00199 
00200 // Given an expression of the form '(A+B)+(D+C)', turn it into '(((A+B)+C)+D)'.
00201 // Note that if D is also part of the expression tree that we recurse to
00202 // linearize it as well.  Besides that case, this does not recurse into A,B, or
00203 // C.
00204 void Reassociate::LinearizeExpr(BinaryOperator *I) {
00205   BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
00206   BinaryOperator *RHS = cast<BinaryOperator>(I->getOperand(1));
00207   assert(isReassociableOp(LHS, I->getOpcode()) &&
00208          isReassociableOp(RHS, I->getOpcode()) &&
00209          "Not an expression that needs linearization?");
00210 
00211   DEBUG(std::cerr << "Linear" << *LHS << *RHS << *I);
00212 
00213   // Move the RHS instruction to live immediately before I, avoiding breaking
00214   // dominator properties.
00215   RHS->moveBefore(I);
00216 
00217   // Move operands around to do the linearization.
00218   I->setOperand(1, RHS->getOperand(0));
00219   RHS->setOperand(0, LHS);
00220   I->setOperand(0, RHS);
00221 
00222   ++NumLinear;
00223   MadeChange = true;
00224   DEBUG(std::cerr << "Linearized: " << *I);
00225 
00226   // If D is part of this expression tree, tail recurse.
00227   if (isReassociableOp(I->getOperand(1), I->getOpcode()))
00228     LinearizeExpr(I);
00229 }
00230 
00231 
00232 /// LinearizeExprTree - Given an associative binary expression tree, traverse
00233 /// all of the uses putting it into canonical form.  This forces a left-linear
00234 /// form of the the expression (((a+b)+c)+d), and collects information about the
00235 /// rank of the non-tree operands.
00236 ///
00237 /// NOTE: These intentionally destroys the expression tree operands (turning
00238 /// them into undef values) to reduce #uses of the values.  This means that the
00239 /// caller MUST use something like RewriteExprTree to put the values back in.
00240 ///
00241 void Reassociate::LinearizeExprTree(BinaryOperator *I,
00242                                     std::vector<ValueEntry> &Ops) {
00243   Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
00244   unsigned Opcode = I->getOpcode();
00245 
00246   // First step, linearize the expression if it is in ((A+B)+(C+D)) form.
00247   BinaryOperator *LHSBO = isReassociableOp(LHS, Opcode);
00248   BinaryOperator *RHSBO = isReassociableOp(RHS, Opcode);
00249 
00250   // If this is a multiply expression tree and it contains internal negations,
00251   // transform them into multiplies by -1 so they can be reassociated.
00252   if (I->getOpcode() == Instruction::Mul) {
00253     if (!LHSBO && LHS->hasOneUse() && BinaryOperator::isNeg(LHS)) {
00254       LHS = LowerNegateToMultiply(cast<Instruction>(LHS));
00255       LHSBO = isReassociableOp(LHS, Opcode);
00256     }
00257     if (!RHSBO && RHS->hasOneUse() && BinaryOperator::isNeg(RHS)) {
00258       RHS = LowerNegateToMultiply(cast<Instruction>(RHS));
00259       RHSBO = isReassociableOp(RHS, Opcode);
00260     }
00261   }
00262 
00263   if (!LHSBO) {
00264     if (!RHSBO) {
00265       // Neither the LHS or RHS as part of the tree, thus this is a leaf.  As
00266       // such, just remember these operands and their rank.
00267       Ops.push_back(ValueEntry(getRank(LHS), LHS));
00268       Ops.push_back(ValueEntry(getRank(RHS), RHS));
00269       
00270       // Clear the leaves out.
00271       I->setOperand(0, UndefValue::get(I->getType()));
00272       I->setOperand(1, UndefValue::get(I->getType()));
00273       return;
00274     } else {
00275       // Turn X+(Y+Z) -> (Y+Z)+X
00276       std::swap(LHSBO, RHSBO);
00277       std::swap(LHS, RHS);
00278       bool Success = !I->swapOperands();
00279       assert(Success && "swapOperands failed");
00280       MadeChange = true;
00281     }
00282   } else if (RHSBO) {
00283     // Turn (A+B)+(C+D) -> (((A+B)+C)+D).  This guarantees the the RHS is not
00284     // part of the expression tree.
00285     LinearizeExpr(I);
00286     LHS = LHSBO = cast<BinaryOperator>(I->getOperand(0));
00287     RHS = I->getOperand(1);
00288     RHSBO = 0;
00289   }
00290 
00291   // Okay, now we know that the LHS is a nested expression and that the RHS is
00292   // not.  Perform reassociation.
00293   assert(!isReassociableOp(RHS, Opcode) && "LinearizeExpr failed!");
00294 
00295   // Move LHS right before I to make sure that the tree expression dominates all
00296   // values.
00297   LHSBO->moveBefore(I);
00298 
00299   // Linearize the expression tree on the LHS.
00300   LinearizeExprTree(LHSBO, Ops);
00301 
00302   // Remember the RHS operand and its rank.
00303   Ops.push_back(ValueEntry(getRank(RHS), RHS));
00304   
00305   // Clear the RHS leaf out.
00306   I->setOperand(1, UndefValue::get(I->getType()));
00307 }
00308 
00309 // RewriteExprTree - Now that the operands for this expression tree are
00310 // linearized and optimized, emit them in-order.  This function is written to be
00311 // tail recursive.
00312 void Reassociate::RewriteExprTree(BinaryOperator *I,
00313                                   std::vector<ValueEntry> &Ops,
00314                                   unsigned i) {
00315   if (i+2 == Ops.size()) {
00316     if (I->getOperand(0) != Ops[i].Op ||
00317         I->getOperand(1) != Ops[i+1].Op) {
00318       Value *OldLHS = I->getOperand(0);
00319       DEBUG(std::cerr << "RA: " << *I);
00320       I->setOperand(0, Ops[i].Op);
00321       I->setOperand(1, Ops[i+1].Op);
00322       DEBUG(std::cerr << "TO: " << *I);
00323       MadeChange = true;
00324       ++NumChanged;
00325       
00326       // If we reassociated a tree to fewer operands (e.g. (1+a+2) -> (a+3)
00327       // delete the extra, now dead, nodes.
00328       RemoveDeadBinaryOp(OldLHS);
00329     }
00330     return;
00331   }
00332   assert(i+2 < Ops.size() && "Ops index out of range!");
00333 
00334   if (I->getOperand(1) != Ops[i].Op) {
00335     DEBUG(std::cerr << "RA: " << *I);
00336     I->setOperand(1, Ops[i].Op);
00337     DEBUG(std::cerr << "TO: " << *I);
00338     MadeChange = true;
00339     ++NumChanged;
00340   }
00341   
00342   BinaryOperator *LHS = cast<BinaryOperator>(I->getOperand(0));
00343   assert(LHS->getOpcode() == I->getOpcode() &&
00344          "Improper expression tree!");
00345   
00346   // Compactify the tree instructions together with each other to guarantee
00347   // that the expression tree is dominated by all of Ops.
00348   LHS->moveBefore(I);
00349   RewriteExprTree(LHS, Ops, i+1);
00350 }
00351 
00352 
00353 
00354 // NegateValue - Insert instructions before the instruction pointed to by BI,
00355 // that computes the negative version of the value specified.  The negative
00356 // version of the value is returned, and BI is left pointing at the instruction
00357 // that should be processed next by the reassociation pass.
00358 //
00359 static Value *NegateValue(Value *V, Instruction *BI) {
00360   // We are trying to expose opportunity for reassociation.  One of the things
00361   // that we want to do to achieve this is to push a negation as deep into an
00362   // expression chain as possible, to expose the add instructions.  In practice,
00363   // this means that we turn this:
00364   //   X = -(A+12+C+D)   into    X = -A + -12 + -C + -D = -12 + -A + -C + -D
00365   // so that later, a: Y = 12+X could get reassociated with the -12 to eliminate
00366   // the constants.  We assume that instcombine will clean up the mess later if
00367   // we introduce tons of unnecessary negation instructions...
00368   //
00369   if (Instruction *I = dyn_cast<Instruction>(V))
00370     if (I->getOpcode() == Instruction::Add && I->hasOneUse()) {
00371       // Push the negates through the add.
00372       I->setOperand(0, NegateValue(I->getOperand(0), BI));
00373       I->setOperand(1, NegateValue(I->getOperand(1), BI));
00374 
00375       // We must move the add instruction here, because the neg instructions do
00376       // not dominate the old add instruction in general.  By moving it, we are
00377       // assured that the neg instructions we just inserted dominate the 
00378       // instruction we are about to insert after them.
00379       //
00380       I->moveBefore(BI);
00381       I->setName(I->getName()+".neg");
00382       return I;
00383     }
00384 
00385   // Insert a 'neg' instruction that subtracts the value from zero to get the
00386   // negation.
00387   //
00388   return BinaryOperator::createNeg(V, V->getName() + ".neg", BI);
00389 }
00390 
00391 /// BreakUpSubtract - If we have (X-Y), and if either X is an add, or if this is
00392 /// only used by an add, transform this into (X+(0-Y)) to promote better
00393 /// reassociation.
00394 static Instruction *BreakUpSubtract(Instruction *Sub) {
00395   // Don't bother to break this up unless either the LHS is an associable add or
00396   // if this is only used by one.
00397   if (!isReassociableOp(Sub->getOperand(0), Instruction::Add) &&
00398       !isReassociableOp(Sub->getOperand(1), Instruction::Add) &&
00399       !(Sub->hasOneUse() &&isReassociableOp(Sub->use_back(), Instruction::Add)))
00400     return 0;
00401 
00402   // Convert a subtract into an add and a neg instruction... so that sub
00403   // instructions can be commuted with other add instructions...
00404   //
00405   // Calculate the negative value of Operand 1 of the sub instruction...
00406   // and set it as the RHS of the add instruction we just made...
00407   //
00408   std::string Name = Sub->getName();
00409   Sub->setName("");
00410   Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
00411   Instruction *New =
00412     BinaryOperator::createAdd(Sub->getOperand(0), NegVal, Name, Sub);
00413 
00414   // Everyone now refers to the add instruction.
00415   Sub->replaceAllUsesWith(New);
00416   Sub->eraseFromParent();
00417 
00418   DEBUG(std::cerr << "Negated: " << *New);
00419   return New;
00420 }
00421 
00422 /// ConvertShiftToMul - If this is a shift of a reassociable multiply or is used
00423 /// by one, change this into a multiply by a constant to assist with further
00424 /// reassociation.
00425 static Instruction *ConvertShiftToMul(Instruction *Shl) {
00426   // If an operand of this shift is a reassociable multiply, or if the shift
00427   // is used by a reassociable multiply or add, turn into a multiply.
00428   if (isReassociableOp(Shl->getOperand(0), Instruction::Mul) ||
00429       (Shl->hasOneUse() && 
00430        (isReassociableOp(Shl->use_back(), Instruction::Mul) ||
00431         isReassociableOp(Shl->use_back(), Instruction::Add)))) {
00432     Constant *MulCst = ConstantInt::get(Shl->getType(), 1);
00433     MulCst = ConstantExpr::getShl(MulCst, cast<Constant>(Shl->getOperand(1)));
00434     
00435     std::string Name = Shl->getName();  Shl->setName("");
00436     Instruction *Mul = BinaryOperator::createMul(Shl->getOperand(0), MulCst,
00437                                                  Name, Shl);
00438     Shl->replaceAllUsesWith(Mul);
00439     Shl->eraseFromParent();
00440     return Mul;
00441   }
00442   return 0;
00443 }
00444 
00445 // Scan backwards and forwards among values with the same rank as element i to
00446 // see if X exists.  If X does not exist, return i.
00447 static unsigned FindInOperandList(std::vector<ValueEntry> &Ops, unsigned i,
00448                                   Value *X) {
00449   unsigned XRank = Ops[i].Rank;
00450   unsigned e = Ops.size();
00451   for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
00452     if (Ops[j].Op == X)
00453       return j;
00454   // Scan backwards
00455   for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
00456     if (Ops[j].Op == X)
00457       return j;
00458   return i;
00459 }
00460 
00461 /// EmitAddTreeOfValues - Emit a tree of add instructions, summing Ops together
00462 /// and returning the result.  Insert the tree before I.
00463 static Value *EmitAddTreeOfValues(Instruction *I, std::vector<Value*> &Ops) {
00464   if (Ops.size() == 1) return Ops.back();
00465   
00466   Value *V1 = Ops.back();
00467   Ops.pop_back();
00468   Value *V2 = EmitAddTreeOfValues(I, Ops);
00469   return BinaryOperator::createAdd(V2, V1, "tmp", I);
00470 }
00471 
00472 /// RemoveFactorFromExpression - If V is an expression tree that is a 
00473 /// multiplication sequence, and if this sequence contains a multiply by Factor,
00474 /// remove Factor from the tree and return the new tree.
00475 Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
00476   BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
00477   if (!BO) return 0;
00478   
00479   std::vector<ValueEntry> Factors;
00480   LinearizeExprTree(BO, Factors);
00481 
00482   bool FoundFactor = false;
00483   for (unsigned i = 0, e = Factors.size(); i != e; ++i)
00484     if (Factors[i].Op == Factor) {
00485       FoundFactor = true;
00486       Factors.erase(Factors.begin()+i);
00487       break;
00488     }
00489   if (!FoundFactor) {
00490     // Make sure to restore the operands to the expression tree.
00491     RewriteExprTree(BO, Factors);
00492     return 0;
00493   }
00494   
00495   if (Factors.size() == 1) return Factors[0].Op;
00496   
00497   RewriteExprTree(BO, Factors);
00498   return BO;
00499 }
00500 
00501 /// FindSingleUseMultiplyFactors - If V is a single-use multiply, recursively
00502 /// add its operands as factors, otherwise add V to the list of factors.
00503 static void FindSingleUseMultiplyFactors(Value *V,
00504                                          std::vector<Value*> &Factors) {
00505   BinaryOperator *BO;
00506   if ((!V->hasOneUse() && !V->use_empty()) ||
00507       !(BO = dyn_cast<BinaryOperator>(V)) ||
00508       BO->getOpcode() != Instruction::Mul) {
00509     Factors.push_back(V);
00510     return;
00511   }
00512   
00513   // Otherwise, add the LHS and RHS to the list of factors.
00514   FindSingleUseMultiplyFactors(BO->getOperand(1), Factors);
00515   FindSingleUseMultiplyFactors(BO->getOperand(0), Factors);
00516 }
00517 
00518 
00519 
00520 Value *Reassociate::OptimizeExpression(BinaryOperator *I,
00521                                        std::vector<ValueEntry> &Ops) {
00522   // Now that we have the linearized expression tree, try to optimize it.
00523   // Start by folding any constants that we found.
00524   bool IterateOptimization = false;
00525   if (Ops.size() == 1) return Ops[0].Op;
00526 
00527   unsigned Opcode = I->getOpcode();
00528   
00529   if (Constant *V1 = dyn_cast<Constant>(Ops[Ops.size()-2].Op))
00530     if (Constant *V2 = dyn_cast<Constant>(Ops.back().Op)) {
00531       Ops.pop_back();
00532       Ops.back().Op = ConstantExpr::get(Opcode, V1, V2);
00533       return OptimizeExpression(I, Ops);
00534     }
00535 
00536   // Check for destructive annihilation due to a constant being used.
00537   if (ConstantIntegral *CstVal = dyn_cast<ConstantIntegral>(Ops.back().Op))
00538     switch (Opcode) {
00539     default: break;
00540     case Instruction::And:
00541       if (CstVal->isNullValue()) {           // ... & 0 -> 0
00542         ++NumAnnihil;
00543         return CstVal;
00544       } else if (CstVal->isAllOnesValue()) { // ... & -1 -> ...
00545         Ops.pop_back();
00546       }
00547       break;
00548     case Instruction::Mul:
00549       if (CstVal->isNullValue()) {           // ... * 0 -> 0
00550         ++NumAnnihil;
00551         return CstVal;
00552       } else if (cast<ConstantInt>(CstVal)->getRawValue() == 1) {
00553         Ops.pop_back();                      // ... * 1 -> ...
00554       }
00555       break;
00556     case Instruction::Or:
00557       if (CstVal->isAllOnesValue()) {        // ... | -1 -> -1
00558         ++NumAnnihil;
00559         return CstVal;
00560       }
00561       // FALLTHROUGH!
00562     case Instruction::Add:
00563     case Instruction::Xor:
00564       if (CstVal->isNullValue())             // ... [|^+] 0 -> ...
00565         Ops.pop_back();
00566       break;
00567     }
00568   if (Ops.size() == 1) return Ops[0].Op;
00569 
00570   // Handle destructive annihilation do to identities between elements in the
00571   // argument list here.
00572   switch (Opcode) {
00573   default: break;
00574   case Instruction::And:
00575   case Instruction::Or:
00576   case Instruction::Xor:
00577     // Scan the operand lists looking for X and ~X pairs, along with X,X pairs.
00578     // If we find any, we can simplify the expression. X&~X == 0, X|~X == -1.
00579     for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
00580       // First, check for X and ~X in the operand list.
00581       assert(i < Ops.size());
00582       if (BinaryOperator::isNot(Ops[i].Op)) {    // Cannot occur for ^.
00583         Value *X = BinaryOperator::getNotArgument(Ops[i].Op);
00584         unsigned FoundX = FindInOperandList(Ops, i, X);
00585         if (FoundX != i) {
00586           if (Opcode == Instruction::And) {   // ...&X&~X = 0
00587             ++NumAnnihil;
00588             return Constant::getNullValue(X->getType());
00589           } else if (Opcode == Instruction::Or) {   // ...|X|~X = -1
00590             ++NumAnnihil;
00591             return ConstantIntegral::getAllOnesValue(X->getType());
00592           }
00593         }
00594       }
00595 
00596       // Next, check for duplicate pairs of values, which we assume are next to
00597       // each other, due to our sorting criteria.
00598       assert(i < Ops.size());
00599       if (i+1 != Ops.size() && Ops[i+1].Op == Ops[i].Op) {
00600         if (Opcode == Instruction::And || Opcode == Instruction::Or) {
00601           // Drop duplicate values.
00602           Ops.erase(Ops.begin()+i);
00603           --i; --e;
00604           IterateOptimization = true;
00605           ++NumAnnihil;
00606         } else {
00607           assert(Opcode == Instruction::Xor);
00608           if (e == 2) {
00609             ++NumAnnihil;
00610             return Constant::getNullValue(Ops[0].Op->getType());
00611           }
00612           // ... X^X -> ...
00613           Ops.erase(Ops.begin()+i, Ops.begin()+i+2);
00614           i -= 1; e -= 2;
00615           IterateOptimization = true;
00616           ++NumAnnihil;
00617         }
00618       }
00619     }
00620     break;
00621 
00622   case Instruction::Add:
00623     // Scan the operand lists looking for X and -X pairs.  If we find any, we
00624     // can simplify the expression. X+-X == 0.
00625     for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
00626       assert(i < Ops.size());
00627       // Check for X and -X in the operand list.
00628       if (BinaryOperator::isNeg(Ops[i].Op)) {
00629         Value *X = BinaryOperator::getNegArgument(Ops[i].Op);
00630         unsigned FoundX = FindInOperandList(Ops, i, X);
00631         if (FoundX != i) {
00632           // Remove X and -X from the operand list.
00633           if (Ops.size() == 2) {
00634             ++NumAnnihil;
00635             return Constant::getNullValue(X->getType());
00636           } else {
00637             Ops.erase(Ops.begin()+i);
00638             if (i < FoundX)
00639               --FoundX;
00640             else
00641               --i;   // Need to back up an extra one.
00642             Ops.erase(Ops.begin()+FoundX);
00643             IterateOptimization = true;
00644             ++NumAnnihil;
00645             --i;     // Revisit element.
00646             e -= 2;  // Removed two elements.
00647           }
00648         }
00649       }
00650     }
00651     
00652 
00653     // Scan the operand list, checking to see if there are any common factors
00654     // between operands.  Consider something like A*A+A*B*C+D.  We would like to
00655     // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
00656     // To efficiently find this, we count the number of times a factor occurs
00657     // for any ADD operands that are MULs.
00658     std::map<Value*, unsigned> FactorOccurrences;
00659     unsigned MaxOcc = 0;
00660     Value *MaxOccVal = 0;
00661     if (!I->getType()->isFloatingPoint()) {
00662       for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
00663         if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op))
00664           if (BOp->getOpcode() == Instruction::Mul && BOp->use_empty()) {
00665             // Compute all of the factors of this added value.
00666             std::vector<Value*> Factors;
00667             FindSingleUseMultiplyFactors(BOp, Factors);
00668             assert(Factors.size() > 1 && "Bad linearize!");
00669             
00670             // Add one to FactorOccurrences for each unique factor in this op.
00671             if (Factors.size() == 2) {
00672               unsigned Occ = ++FactorOccurrences[Factors[0]];
00673               if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[0]; }
00674               if (Factors[0] != Factors[1]) {   // Don't double count A*A.
00675                 Occ = ++FactorOccurrences[Factors[1]];
00676                 if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[1]; }
00677               }
00678             } else {
00679               std::set<Value*> Duplicates;
00680               for (unsigned i = 0, e = Factors.size(); i != e; ++i)
00681                 if (Duplicates.insert(Factors[i]).second) {
00682                   unsigned Occ = ++FactorOccurrences[Factors[i]];
00683                   if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factors[i]; }
00684                 }
00685             }
00686           }
00687       }
00688     }
00689 
00690     // If any factor occurred more than one time, we can pull it out.
00691     if (MaxOcc > 1) {
00692       DEBUG(std::cerr << "\nFACTORING [" << MaxOcc << "]: "
00693                       << *MaxOccVal << "\n");
00694       
00695       // Create a new instruction that uses the MaxOccVal twice.  If we don't do
00696       // this, we could otherwise run into situations where removing a factor
00697       // from an expression will drop a use of maxocc, and this can cause 
00698       // RemoveFactorFromExpression on successive values to behave differently.
00699       Instruction *DummyInst = BinaryOperator::createAdd(MaxOccVal, MaxOccVal);
00700       std::vector<Value*> NewMulOps;
00701       for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
00702         if (Value *V = RemoveFactorFromExpression(Ops[i].Op, MaxOccVal)) {
00703           NewMulOps.push_back(V);
00704           Ops.erase(Ops.begin()+i);
00705           --i; --e;
00706         }
00707       }
00708       
00709       // No need for extra uses anymore.
00710       delete DummyInst;
00711 
00712       unsigned NumAddedValues = NewMulOps.size();
00713       Value *V = EmitAddTreeOfValues(I, NewMulOps);
00714       Value *V2 = BinaryOperator::createMul(V, MaxOccVal, "tmp", I);
00715 
00716       // Now that we have inserted V and its sole use, optimize it. This allows
00717       // us to handle cases that require multiple factoring steps, such as this:
00718       // A*A*B + A*A*C   -->   A*(A*B+A*C)   -->   A*(A*(B+C))
00719       if (NumAddedValues > 1)
00720         ReassociateExpression(cast<BinaryOperator>(V));
00721       
00722       ++NumFactor;
00723       
00724       if (Ops.size() == 0)
00725         return V2;
00726 
00727       // Add the new value to the list of things being added.
00728       Ops.insert(Ops.begin(), ValueEntry(getRank(V2), V2));
00729       
00730       // Rewrite the tree so that there is now a use of V.
00731       RewriteExprTree(I, Ops);
00732       return OptimizeExpression(I, Ops);
00733     }
00734     break;
00735   //case Instruction::Mul:
00736   }
00737 
00738   if (IterateOptimization)
00739     return OptimizeExpression(I, Ops);
00740   return 0;
00741 }
00742 
00743 
00744 /// ReassociateBB - Inspect all of the instructions in this basic block,
00745 /// reassociating them as we go.
00746 void Reassociate::ReassociateBB(BasicBlock *BB) {
00747   for (BasicBlock::iterator BBI = BB->begin(); BBI != BB->end(); ) {
00748     Instruction *BI = BBI++;
00749     if (BI->getOpcode() == Instruction::Shl &&
00750         isa<ConstantInt>(BI->getOperand(1)))
00751       if (Instruction *NI = ConvertShiftToMul(BI)) {
00752         MadeChange = true;
00753         BI = NI;
00754       }
00755 
00756     // Reject cases where it is pointless to do this.
00757     if (!isa<BinaryOperator>(BI) || BI->getType()->isFloatingPoint())
00758       continue;  // Floating point ops are not associative.
00759 
00760     // If this is a subtract instruction which is not already in negate form,
00761     // see if we can convert it to X+-Y.
00762     if (BI->getOpcode() == Instruction::Sub) {
00763       if (!BinaryOperator::isNeg(BI)) {
00764         if (Instruction *NI = BreakUpSubtract(BI)) {
00765           MadeChange = true;
00766           BI = NI;
00767         }
00768       } else {
00769         // Otherwise, this is a negation.  See if the operand is a multiply tree
00770         // and if this is not an inner node of a multiply tree.
00771         if (isReassociableOp(BI->getOperand(1), Instruction::Mul) &&
00772             (!BI->hasOneUse() ||
00773              !isReassociableOp(BI->use_back(), Instruction::Mul))) {
00774           BI = LowerNegateToMultiply(BI);
00775           MadeChange = true;
00776         }
00777       }
00778     }
00779 
00780     // If this instruction is a commutative binary operator, process it.
00781     if (!BI->isAssociative()) continue;
00782     BinaryOperator *I = cast<BinaryOperator>(BI);
00783 
00784     // If this is an interior node of a reassociable tree, ignore it until we
00785     // get to the root of the tree, to avoid N^2 analysis.
00786     if (I->hasOneUse() && isReassociableOp(I->use_back(), I->getOpcode()))
00787       continue;
00788 
00789     // If this is an add tree that is used by a sub instruction, ignore it 
00790     // until we process the subtract.
00791     if (I->hasOneUse() && I->getOpcode() == Instruction::Add &&
00792         cast<Instruction>(I->use_back())->getOpcode() == Instruction::Sub)
00793       continue;
00794 
00795     ReassociateExpression(I);
00796   }
00797 }
00798 
00799 void Reassociate::ReassociateExpression(BinaryOperator *I) {
00800   
00801   // First, walk the expression tree, linearizing the tree, collecting
00802   std::vector<ValueEntry> Ops;
00803   LinearizeExprTree(I, Ops);
00804   
00805   DEBUG(std::cerr << "RAIn:\t"; PrintOps(I, Ops);
00806         std::cerr << "\n");
00807   
00808   // Now that we have linearized the tree to a list and have gathered all of
00809   // the operands and their ranks, sort the operands by their rank.  Use a
00810   // stable_sort so that values with equal ranks will have their relative
00811   // positions maintained (and so the compiler is deterministic).  Note that
00812   // this sorts so that the highest ranking values end up at the beginning of
00813   // the vector.
00814   std::stable_sort(Ops.begin(), Ops.end());
00815   
00816   // OptimizeExpression - Now that we have the expression tree in a convenient
00817   // sorted form, optimize it globally if possible.
00818   if (Value *V = OptimizeExpression(I, Ops)) {
00819     // This expression tree simplified to something that isn't a tree,
00820     // eliminate it.
00821     DEBUG(std::cerr << "Reassoc to scalar: " << *V << "\n");
00822     I->replaceAllUsesWith(V);
00823     RemoveDeadBinaryOp(I);
00824     return;
00825   }
00826   
00827   // We want to sink immediates as deeply as possible except in the case where
00828   // this is a multiply tree used only by an add, and the immediate is a -1.
00829   // In this case we reassociate to put the negation on the outside so that we
00830   // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
00831   if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
00832       cast<Instruction>(I->use_back())->getOpcode() == Instruction::Add &&
00833       isa<ConstantInt>(Ops.back().Op) &&
00834       cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
00835     Ops.insert(Ops.begin(), Ops.back());
00836     Ops.pop_back();
00837   }
00838   
00839   DEBUG(std::cerr << "RAOut:\t"; PrintOps(I, Ops);
00840         std::cerr << "\n");
00841   
00842   if (Ops.size() == 1) {
00843     // This expression tree simplified to something that isn't a tree,
00844     // eliminate it.
00845     I->replaceAllUsesWith(Ops[0].Op);
00846     RemoveDeadBinaryOp(I);
00847   } else {
00848     // Now that we ordered and optimized the expressions, splat them back into
00849     // the expression tree, removing any unneeded nodes.
00850     RewriteExprTree(I, Ops);
00851   }
00852 }
00853 
00854 
00855 bool Reassociate::runOnFunction(Function &F) {
00856   // Recalculate the rank map for F
00857   BuildRankMap(F);
00858 
00859   MadeChange = false;
00860   for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
00861     ReassociateBB(FI);
00862 
00863   // We are done with the rank map...
00864   RankMap.clear();
00865   ValueRankMap.clear();
00866   return MadeChange;
00867 }
00868