1 //===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===// 2 // 3 // InductionVariableSimplify - Transform induction variables in a program 4 // to all use a single cannonical induction variable per loop. 5 // 6 //===----------------------------------------------------------------------===// 7 8 #include "llvm/Transforms/Scalar.h" 9 #include "llvm/Analysis/InductionVariable.h" 10 #include "llvm/Analysis/LoopInfo.h" 11 #include "llvm/iPHINode.h" 12 #include "llvm/iOther.h" 13 #include "llvm/Type.h" 14 #include "llvm/Constants.h" 15 #include "llvm/Support/CFG.h" 16 #include "Support/STLExtras.h" 17 #include "Support/StatisticReporter.h" 18 19 static Statistic<> NumRemoved ("indvars\t\t- Number of aux indvars removed"); 20 static Statistic<> NumInserted("indvars\t\t- Number of cannonical indvars added"); 21 22 #if 0 23 #define DEBUG 24 #include "llvm/Analysis/Writer.h" 25 #endif 26 27 // InsertCast - Cast Val to Ty, setting a useful name on the cast if Val has a 28 // name... 29 // 30 static Instruction *InsertCast(Instruction *Val, const Type *Ty, 31 BasicBlock::iterator It) { 32 Instruction *Cast = new CastInst(Val, Ty); 33 if (Val->hasName()) Cast->setName(Val->getName()+"-casted"); 34 Val->getParent()->getInstList().insert(It, Cast); 35 return Cast; 36 } 37 38 static bool TransformLoop(LoopInfo *Loops, Loop *Loop) { 39 // Transform all subloops before this loop... 40 bool Changed = reduce_apply_bool(Loop->getSubLoops().begin(), 41 Loop->getSubLoops().end(), 42 std::bind1st(std::ptr_fun(TransformLoop), Loops)); 43 // Get the header node for this loop. All of the phi nodes that could be 44 // induction variables must live in this basic block. 45 // 46 BasicBlock *Header = Loop->getBlocks().front(); 47 48 // Loop over all of the PHI nodes in the basic block, calculating the 49 // induction variables that they represent... stuffing the induction variable 50 // info into a vector... 51 // 52 std::vector<InductionVariable> IndVars; // Induction variables for block 53 for (BasicBlock::iterator I = Header->begin(); 54 PHINode *PN = dyn_cast<PHINode>(*I); ++I) 55 IndVars.push_back(InductionVariable(PN, Loops)); 56 57 // If there are no phi nodes in this basic block, there can't be indvars... 58 if (IndVars.empty()) return Changed; 59 60 // Loop over the induction variables, looking for a cannonical induction 61 // variable, and checking to make sure they are not all unknown induction 62 // variables. 63 // 64 bool FoundIndVars = false; 65 InductionVariable *Cannonical = 0; 66 for (unsigned i = 0; i < IndVars.size(); ++i) { 67 if (IndVars[i].InductionType == InductionVariable::Cannonical) 68 Cannonical = &IndVars[i]; 69 if (IndVars[i].InductionType != InductionVariable::Unknown) 70 FoundIndVars = true; 71 } 72 73 // No induction variables, bail early... don't add a cannonnical indvar 74 if (!FoundIndVars) return Changed; 75 76 // Okay, we want to convert other induction variables to use a cannonical 77 // indvar. If we don't have one, add one now... 78 if (!Cannonical) { 79 // Create the PHI node for the new induction variable 80 PHINode *PN = new PHINode(Type::UIntTy, "cann-indvar"); 81 82 // Insert the phi node at the end of the other phi nodes... 83 Header->getInstList().insert(Header->begin()+IndVars.size(), PN); 84 85 // Create the increment instruction to add one to the counter... 86 Instruction *Add = BinaryOperator::create(Instruction::Add, PN, 87 ConstantUInt::get(Type::UIntTy,1), 88 "add1-indvar"); 89 90 // Insert the add instruction after all of the PHI nodes... 91 Header->getInstList().insert(Header->begin()+(IndVars.size()+1), Add); 92 93 // Figure out which block is incoming and which is the backedge for the loop 94 BasicBlock *Incoming, *BackEdgeBlock; 95 pred_iterator PI = pred_begin(Header); 96 assert(PI != pred_end(Header) && "Loop headers should have 2 preds!"); 97 if (Loop->contains(*PI)) { // First pred is back edge... 98 BackEdgeBlock = *PI++; 99 Incoming = *PI++; 100 } else { 101 Incoming = *PI++; 102 BackEdgeBlock = *PI++; 103 } 104 assert(PI == pred_end(Header) && "Loop headers should have 2 preds!"); 105 106 // Add incoming values for the PHI node... 107 PN->addIncoming(Constant::getNullValue(Type::UIntTy), Incoming); 108 PN->addIncoming(Add, BackEdgeBlock); 109 110 // Analyze the new induction variable... 111 IndVars.push_back(InductionVariable(PN, Loops)); 112 assert(IndVars.back().InductionType == InductionVariable::Cannonical && 113 "Just inserted cannonical indvar that is not cannonical!"); 114 Cannonical = &IndVars.back(); 115 ++NumInserted; 116 Changed = true; 117 } 118 119 #ifdef DEBUG 120 cerr << "Induction variables:\n"; 121 #endif 122 123 // Get the current loop iteration count, which is always the value of the 124 // cannonical phi node... 125 // 126 PHINode *IterCount = Cannonical->Phi; 127 128 // Loop through and replace all of the auxillary induction variables with 129 // references to the primary induction variable... 130 // 131 unsigned InsertPos = IndVars.size(); 132 for (unsigned i = 0; i < IndVars.size(); ++i) { 133 InductionVariable *IV = &IndVars[i]; 134 #ifdef DEBUG 135 cerr << IndVars[i]; 136 #endif 137 // Don't modify the cannonical indvar or unrecognized indvars... 138 if (IV != Cannonical && IV->InductionType != InductionVariable::Unknown) { 139 Instruction *Val = IterCount; 140 if (!isa<ConstantInt>(IV->Step) || // If the step != 1 141 !cast<ConstantInt>(IV->Step)->equalsInt(1)) { 142 std::string Name; // Create a scale by the step value... 143 if (IV->Phi->hasName()) Name = IV->Phi->getName()+"-scale"; 144 145 // If the types are not compatible, insert a cast now... 146 if (Val->getType() != IV->Step->getType()) 147 Val = InsertCast(Val, IV->Step->getType(), 148 Header->begin()+InsertPos++); 149 150 Val = BinaryOperator::create(Instruction::Mul, Val, IV->Step, Name); 151 // Insert the phi node at the end of the other phi nodes... 152 Header->getInstList().insert(Header->begin()+InsertPos++, Val); 153 } 154 155 if (!isa<Constant>(IV->Start) || // If the start != 0 156 !cast<Constant>(IV->Start)->isNullValue()) { 157 std::string Name; // Create a offset by the start value... 158 if (IV->Phi->hasName()) Name = IV->Phi->getName()+"-offset"; 159 160 // If the types are not compatible, insert a cast now... 161 if (Val->getType() != IV->Start->getType()) 162 Val = InsertCast(Val, IV->Start->getType(), 163 Header->begin()+InsertPos++); 164 165 Val = BinaryOperator::create(Instruction::Add, Val, IV->Start, Name); 166 // Insert the phi node at the end of the other phi nodes... 167 Header->getInstList().insert(Header->begin()+InsertPos++, Val); 168 } 169 170 // If the PHI node has a different type than val is, insert a cast now... 171 if (Val->getType() != IV->Phi->getType()) 172 Val = InsertCast(Val, IV->Phi->getType(), 173 Header->begin()+InsertPos++); 174 175 // Replace all uses of the old PHI node with the new computed value... 176 IV->Phi->replaceAllUsesWith(Val); 177 178 // Move the PHI name to it's new equivalent value... 179 std::string OldName = IV->Phi->getName(); 180 IV->Phi->setName(""); 181 Val->setName(OldName); 182 183 // Delete the old, now unused, phi node... 184 Header->getInstList().remove(IV->Phi); 185 delete IV->Phi; 186 InsertPos--; // Deleted an instr, decrement insert position 187 Changed = true; 188 ++NumRemoved; 189 } 190 } 191 192 return Changed; 193 } 194 195 namespace { 196 struct InductionVariableSimplify : public FunctionPass { 197 const char *getPassName() const { 198 return "Induction Variable Cannonicalize"; 199 } 200 201 virtual bool runOnFunction(Function *F) { 202 LoopInfo &LI = getAnalysis<LoopInfo>(); 203 204 // Induction Variables live in the header nodes of loops 205 return reduce_apply_bool(LI.getTopLevelLoops().begin(), 206 LI.getTopLevelLoops().end(), 207 std::bind1st(std::ptr_fun(TransformLoop), &LI)); 208 } 209 210 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 211 AU.addRequired(LoopInfo::ID); 212 AU.preservesCFG(); 213 } 214 }; 215 } 216 217 Pass *createIndVarSimplifyPass() { 218 return new InductionVariableSimplify(); 219 } 220 221