1 //===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===//
3 // InductionVariableSimplify - Transform induction variables in a program
4 // to all use a single cannonical induction variable per loop.
6 //===----------------------------------------------------------------------===//
8 #include "llvm/Transforms/Scalar/IndVarSimplify.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/BasicBlock.h"
15 #include "llvm/ConstantVals.h"
16 #include "llvm/Pass.h"
17 #include "llvm/Support/CFG.h"
18 #include "Support/STLExtras.h"
22 #include "llvm/Analysis/Writer.h"
25 // InsertCast - Cast Val to Ty, setting a useful name on the cast if Val has a
28 static Instruction *InsertCast(Instruction *Val, const Type *Ty,
29 BasicBlock::iterator It) {
30 Instruction *Cast = new CastInst(Val, Ty);
31 if (Val->hasName()) Cast->setName(Val->getName()+"-casted");
32 Val->getParent()->getInstList().insert(It, Cast);
36 static bool TransformLoop(cfg::LoopInfo *Loops, cfg::Loop *Loop) {
37 // Transform all subloops before this loop...
38 bool Changed = reduce_apply_bool(Loop->getSubLoops().begin(),
39 Loop->getSubLoops().end(),
40 std::bind1st(std::ptr_fun(TransformLoop), Loops));
41 // Get the header node for this loop. All of the phi nodes that could be
42 // induction variables must live in this basic block.
43 BasicBlock *Header = (BasicBlock*)Loop->getBlocks().front();
45 // Loop over all of the PHI nodes in the basic block, calculating the
46 // induction variables that they represent... stuffing the induction variable
47 // info into a vector...
49 std::vector<InductionVariable> IndVars; // Induction variables for block
50 for (BasicBlock::iterator I = Header->begin();
51 PHINode *PN = dyn_cast<PHINode>(*I); ++I)
52 IndVars.push_back(InductionVariable(PN, Loops));
54 // If there are no phi nodes in this basic block, there can't be indvars...
55 if (IndVars.empty()) return Changed;
57 // Loop over the induction variables, looking for a cannonical induction
58 // variable, and checking to make sure they are not all unknown induction
61 bool FoundIndVars = false;
62 InductionVariable *Cannonical = 0;
63 for (unsigned i = 0; i < IndVars.size(); ++i) {
64 if (IndVars[i].InductionType == InductionVariable::Cannonical)
65 Cannonical = &IndVars[i];
66 if (IndVars[i].InductionType != InductionVariable::Unknown)
70 // No induction variables, bail early... don't add a cannonnical indvar
71 if (!FoundIndVars) return Changed;
73 // Okay, we want to convert other induction variables to use a cannonical
74 // indvar. If we don't have one, add one now...
76 // Create the PHI node for the new induction variable
77 PHINode *PN = new PHINode(Type::UIntTy, "cann-indvar");
79 // Insert the phi node at the end of the other phi nodes...
80 Header->getInstList().insert(Header->begin()+IndVars.size(), PN);
82 // Create the increment instruction to add one to the counter...
83 Instruction *Add = BinaryOperator::create(Instruction::Add, PN,
84 ConstantUInt::get(Type::UIntTy,1),
87 // Insert the add instruction after all of the PHI nodes...
88 Header->getInstList().insert(Header->begin()+(IndVars.size()+1), Add);
90 // Figure out which block is incoming and which is the backedge for the loop
91 BasicBlock *Incoming, *BackEdgeBlock;
92 pred_iterator PI = pred_begin(Header);
93 assert(PI != pred_end(Header) && "Loop headers should have 2 preds!");
94 if (Loop->contains(*PI)) { // First pred is back edge...
95 BackEdgeBlock = *PI++;
99 BackEdgeBlock = *PI++;
101 assert(PI == pred_end(Header) && "Loop headers should have 2 preds!");
103 // Add incoming values for the PHI node...
104 PN->addIncoming(Constant::getNullConstant(Type::UIntTy), Incoming);
105 PN->addIncoming(Add, BackEdgeBlock);
107 // Analyze the new induction variable...
108 IndVars.push_back(InductionVariable(PN, Loops));
109 assert(IndVars.back().InductionType == InductionVariable::Cannonical &&
110 "Just inserted cannonical indvar that is not cannonical!");
111 Cannonical = &IndVars.back();
116 cerr << "Induction variables:\n";
119 // Get the current loop iteration count, which is always the value of the
120 // cannonical phi node...
122 PHINode *IterCount = Cannonical->Phi;
124 // Loop through and replace all of the auxillary induction variables with
125 // references to the primary induction variable...
127 unsigned InsertPos = IndVars.size();
128 for (unsigned i = 0; i < IndVars.size(); ++i) {
129 InductionVariable *IV = &IndVars[i];
133 // Don't modify the cannonical indvar or unrecognized indvars...
134 if (IV != Cannonical && IV->InductionType != InductionVariable::Unknown) {
135 Instruction *Val = IterCount;
136 if (!isa<ConstantInt>(IV->Step) || // If the step != 1
137 !cast<ConstantInt>(IV->Step)->equalsInt(1)) {
138 std::string Name; // Create a scale by the step value...
139 if (IV->Phi->hasName()) Name = IV->Phi->getName()+"-scale";
141 // If the types are not compatible, insert a cast now...
142 if (Val->getType() != IV->Step->getType())
143 Val = InsertCast(Val, IV->Step->getType(),
144 Header->begin()+InsertPos++);
146 Val = BinaryOperator::create(Instruction::Mul, Val, IV->Step, Name);
147 // Insert the phi node at the end of the other phi nodes...
148 Header->getInstList().insert(Header->begin()+InsertPos++, Val);
151 if (!isa<Constant>(IV->Start) || // If the start != 0
152 !cast<Constant>(IV->Start)->isNullValue()) {
153 std::string Name; // Create a offset by the start value...
154 if (IV->Phi->hasName()) Name = IV->Phi->getName()+"-offset";
156 // If the types are not compatible, insert a cast now...
157 if (Val->getType() != IV->Start->getType())
158 Val = InsertCast(Val, IV->Start->getType(),
159 Header->begin()+InsertPos++);
161 Val = BinaryOperator::create(Instruction::Add, Val, IV->Start, Name);
162 // Insert the phi node at the end of the other phi nodes...
163 Header->getInstList().insert(Header->begin()+InsertPos++, Val);
166 // If the PHI node has a different type than val is, insert a cast now...
167 if (Val->getType() != IV->Phi->getType())
168 Val = InsertCast(Val, IV->Phi->getType(),
169 Header->begin()+InsertPos++);
171 // Replace all uses of the old PHI node with the new computed value...
172 IV->Phi->replaceAllUsesWith(Val);
174 // Move the PHI name to it's new equivalent value...
175 std::string OldName = IV->Phi->getName();
176 IV->Phi->setName("");
177 Val->setName(OldName);
179 // Delete the old, now unused, phi node...
180 Header->getInstList().remove(IV->Phi);
182 InsertPos--; // Deleted an instr, decrement insert position
190 static bool doit(Method *M, cfg::LoopInfo &Loops) {
191 // Induction Variables live in the header nodes of the loops of the method...
192 return reduce_apply_bool(Loops.getTopLevelLoops().begin(),
193 Loops.getTopLevelLoops().end(),
194 std::bind1st(std::ptr_fun(TransformLoop), &Loops));
199 struct InductionVariableSimplify : public MethodPass {
200 virtual bool runOnMethod(Method *M) {
201 return doit(M, getAnalysis<cfg::LoopInfo>());
204 virtual void getAnalysisUsageInfo(Pass::AnalysisSet &Required,
205 Pass::AnalysisSet &Destroyed,
206 Pass::AnalysisSet &Provided) {
207 Required.push_back(cfg::LoopInfo::ID);
212 Pass *createIndVarSimplifyPass() {
213 return new InductionVariableSimplify();