1 //===- InductionVariable.cpp - Induction variable classification ----------===//
3 // This file implements identification and classification of induction
4 // variables. Induction variables must contain a PHI node that exists in a
5 // loop header. Because of this, they are identified an managed by this PHI
8 // Induction variables are classified into a type. Knowing that an induction
9 // variable is of a specific type can constrain the values of the start and
10 // step. For example, a SimpleLinear induction variable must have a start and
11 // step values that are constants.
13 // Induction variables can be created with or without loop information. If no
14 // loop information is available, induction variables cannot be recognized to be
15 // more than SimpleLinear variables.
17 //===----------------------------------------------------------------------===//
19 #include "llvm/Analysis/InductionVariable.h"
20 #include "llvm/Analysis/LoopInfo.h"
21 #include "llvm/Analysis/Expressions.h"
22 #include "llvm/BasicBlock.h"
23 #include "llvm/iPHINode.h"
24 #include "llvm/iOperators.h"
25 #include "llvm/iTerminators.h"
26 #include "llvm/Type.h"
27 #include "llvm/Constants.h"
28 #include "llvm/Support/CFG.h"
29 #include "llvm/Assembly/Writer.h"
30 #include "Support/Debug.h"
32 static bool isLoopInvariant(const Value *V, const Loop *L) {
33 if (const Instruction *I = dyn_cast<Instruction>(V))
34 return !L->contains(I->getParent());
35 // non-instructions all dominate instructions/blocks
39 enum InductionVariable::iType
40 InductionVariable::Classify(const Value *Start, const Value *Step,
42 // Check for canonical and simple linear expressions now...
43 if (const ConstantInt *CStart = dyn_cast<ConstantInt>(Start))
44 if (const ConstantInt *CStep = dyn_cast<ConstantInt>(Step)) {
45 if (CStart->isNullValue() && CStep->equalsInt(1))
51 // Without loop information, we cannot do any better, so bail now...
52 if (L == 0) return Unknown;
54 if (isLoopInvariant(Start, L) && isLoopInvariant(Step, L))
59 // Create an induction variable for the specified value. If it is a PHI, and
60 // if it's recognizable, classify it and fill in instance variables.
62 InductionVariable::InductionVariable(PHINode *P, LoopInfo *LoopInfo): End(0) {
63 InductionType = Unknown; // Assume the worst
66 // If the PHI node has more than two predecessors, we don't know how to
69 if (Phi->getNumIncomingValues() != 2) return;
71 // FIXME: Handle FP induction variables.
72 if (Phi->getType() == Type::FloatTy || Phi->getType() == Type::DoubleTy)
75 // If we have loop information, make sure that this PHI node is in the header
78 const Loop *L = LoopInfo ? LoopInfo->getLoopFor(Phi->getParent()) : 0;
79 if (L && L->getHeader() != Phi->getParent())
82 Value *V1 = Phi->getIncomingValue(0);
83 Value *V2 = Phi->getIncomingValue(1);
85 if (L == 0) { // No loop information? Base everything on expression analysis
86 ExprType E1 = ClassifyExpression(V1);
87 ExprType E2 = ClassifyExpression(V2);
89 if (E1.ExprTy > E2.ExprTy) // Make E1 be the simpler expression
92 // E1 must be a constant incoming value, and E2 must be a linear expression
93 // with respect to the PHI node.
95 if (E1.ExprTy > ExprType::Constant || E2.ExprTy != ExprType::Linear ||
99 // Okay, we have found an induction variable. Save the start and step values
100 const Type *ETy = Phi->getType();
101 if (isa<PointerType>(ETy)) ETy = Type::ULongTy;
103 Start = (Value*)(E1.Offset ? E1.Offset : ConstantInt::get(ETy, 0));
104 Step = (Value*)(E2.Offset ? E2.Offset : ConstantInt::get(ETy, 0));
106 // Okay, at this point, we know that we have loop information...
108 // Make sure that V1 is the incoming value, and V2 is from the backedge of
110 if (L->contains(Phi->getIncomingBlock(0))) // Wrong order. Swap now.
113 Start = V1; // We know that Start has to be loop invariant...
116 if (V2 == Phi) { // referencing the PHI directly? Must have zero step
117 Step = Constant::getNullValue(Phi->getType());
118 } else if (BinaryOperator *I = dyn_cast<BinaryOperator>(V2)) {
119 // TODO: This could be much better...
120 if (I->getOpcode() == Instruction::Add) {
121 if (I->getOperand(0) == Phi)
122 Step = I->getOperand(1);
123 else if (I->getOperand(1) == Phi)
124 Step = I->getOperand(0);
128 if (Step == 0) { // Unrecognized step value...
129 ExprType StepE = ClassifyExpression(V2);
130 if (StepE.ExprTy != ExprType::Linear ||
131 StepE.Var != Phi) return;
133 const Type *ETy = Phi->getType();
134 if (isa<PointerType>(ETy)) ETy = Type::ULongTy;
135 Step = (Value*)(StepE.Offset ? StepE.Offset : ConstantInt::get(ETy, 0));
136 } else { // We were able to get a step value, simplify with expr analysis
137 ExprType StepE = ClassifyExpression(Step);
138 if (StepE.ExprTy == ExprType::Linear && StepE.Offset == 0) {
139 // No offset from variable? Grab the variable
141 } else if (StepE.ExprTy == ExprType::Constant) {
143 Step = (Value*)StepE.Offset;
145 Step = Constant::getNullValue(Step->getType());
146 const Type *ETy = Phi->getType();
147 if (isa<PointerType>(ETy)) ETy = Type::ULongTy;
148 Step = (Value*)(StepE.Offset ? StepE.Offset : ConstantInt::get(ETy,0));
153 // Classify the induction variable type now...
154 InductionType = InductionVariable::Classify(Start, Step, L);
158 Value *InductionVariable::getExecutionCount(LoopInfo *LoopInfo) {
159 if (InductionType != Canonical) return 0;
161 DEBUG(std::cerr << "entering getExecutionCount\n");
163 // Don't recompute if already available
165 DEBUG(std::cerr << "returning cached End value.\n");
169 const Loop *L = LoopInfo ? LoopInfo->getLoopFor(Phi->getParent()) : 0;
171 DEBUG(std::cerr << "null loop. oops\n");
175 // >1 backedge => cannot predict number of iterations
176 if (Phi->getNumIncomingValues() != 2) {
177 DEBUG(std::cerr << ">2 incoming values. oops\n");
181 // Find final node: predecesor of the loop header that's also an exit
182 BasicBlock *terminator = 0;
183 for (pred_iterator PI = pred_begin(L->getHeader()),
184 PE = pred_end(L->getHeader()); PI != PE; ++PI)
185 if (L->isLoopExit(*PI)) {
190 // Break in the loop => cannot predict number of iterations
191 // break: any block which is an exit node whose successor is not in loop,
192 // and this block is not marked as the terminator
194 const std::vector<BasicBlock*> &blocks = L->getBlocks();
195 for (std::vector<BasicBlock*>::const_iterator I = blocks.begin(),
196 e = blocks.end(); I != e; ++I)
197 if (L->isLoopExit(*I) && *I != terminator)
198 for (succ_iterator SI = succ_begin(*I), SE = succ_end(*I); SI != SE; ++SI)
199 if (!L->contains(*SI)) {
200 DEBUG(std::cerr << "break found in loop");
204 BranchInst *B = dyn_cast<BranchInst>(terminator->getTerminator());
206 DEBUG(std::cerr << "Terminator is not a cond branch!");
209 SetCondInst *SCI = dyn_cast<SetCondInst>(B->getCondition());
211 DEBUG(std::cerr << "Not a cond branch on setcc!\n");
215 DEBUG(std::cerr << "sci:" << *SCI);
216 Value *condVal0 = SCI->getOperand(0);
217 Value *condVal1 = SCI->getOperand(1);
219 // The induction variable is the one coming from the backedge
220 Value *indVar = Phi->getIncomingValue(L->contains(Phi->getIncomingBlock(1)));
223 // Check to see if indVar is one of the parameters in SCI and if the other is
224 // loop-invariant, it is the UB
225 if (indVar == condVal0) {
226 if (isLoopInvariant(condVal1, L))
229 DEBUG(std::cerr << "not loop invariant 1\n");
232 } else if (indVar == condVal1) {
233 if (isLoopInvariant(condVal0, L))
236 DEBUG(std::cerr << "not loop invariant 0\n");
240 DEBUG(std::cerr << "Loop condition doesn't directly uses indvar\n");
244 switch (SCI->getOpcode()) {
245 case Instruction::SetLT:
246 case Instruction::SetNE: return End; // already done
247 case Instruction::SetLE:
248 // if compared to a constant int N, then predict N+1 iterations
249 if (ConstantSInt *ubSigned = dyn_cast<ConstantSInt>(End)) {
250 DEBUG(std::cerr << "signed int constant\n");
251 return ConstantSInt::get(ubSigned->getType(), ubSigned->getValue()+1);
252 } else if (ConstantUInt *ubUnsigned = dyn_cast<ConstantUInt>(End)) {
253 DEBUG(std::cerr << "unsigned int constant\n");
254 return ConstantUInt::get(ubUnsigned->getType(),
255 ubUnsigned->getValue()+1);
257 DEBUG(std::cerr << "symbolic bound\n");
258 // new expression N+1, insert right before the SCI. FIXME: If End is loop
259 // invariant, then so is this expression. We should insert it in the loop
260 // preheader if it exists.
261 return BinaryOperator::create(Instruction::Add, End,
262 ConstantInt::get(End->getType(), 1),
267 return 0; // cannot predict
272 void InductionVariable::print(std::ostream &o) const {
273 switch (InductionType) {
274 case InductionVariable::Canonical: o << "Canonical "; break;
275 case InductionVariable::SimpleLinear: o << "SimpleLinear "; break;
276 case InductionVariable::Linear: o << "Linear "; break;
277 case InductionVariable::Unknown: o << "Unrecognized "; break;
279 o << "Induction Variable: ";
281 WriteAsOperand(o, Phi);
286 if (InductionType == InductionVariable::Unknown) return;
288 o << " Start = "; WriteAsOperand(o, Start);
289 o << " Step = " ; WriteAsOperand(o, Step);
291 o << " End = " ; WriteAsOperand(o, End);