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//===- llvm/Analysis/InductionVariable.h - Induction variable ----*- C++ -*--=//
//
// This interface is used to identify and classify induction variables that
// exist in the program. Induction variables must contain a PHI node that
// exists in a loop header. Because of this, they are identified an managed by
// this PHI node.
//
// Induction variables are classified into a type. Knowing that an induction
// variable is of a specific type can constrain the values of the start and
// step. For example, a SimpleLinear induction variable must have a start and
// step values that are constants.
//
// Induction variables can be created with or without loop information. If no
// loop information is available, induction variables cannot be recognized to be
// more than SimpleLinear variables.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/InductionVariable.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/Expressions.h"
#include "llvm/iPHINode.h"
#include "llvm/InstrTypes.h"
#include "llvm/Type.h"
#include "llvm/ConstantVals.h"
using analysis::ExprType;
static bool isLoopInvariant(const Value *V, const cfg::Loop *L) {
if (isa<Constant>(V) || isa<Argument>(V) || isa<GlobalValue>(V))
return true;
const Instruction *I = cast<Instruction>(V);
const BasicBlock *BB = I->getParent();
return !L->contains(BB);
}
enum InductionVariable::iType
InductionVariable::Classify(const Value *Start, const Value *Step,
const cfg::Loop *L = 0) {
// Check for cannonical and simple linear expressions now...
if (ConstantInt *CStart = dyn_cast<ConstantInt>(Start))
if (ConstantInt *CStep = dyn_cast<ConstantInt>(Step)) {
if (CStart->equalsInt(0) && CStep->equalsInt(1))
return Cannonical;
else
return SimpleLinear;
}
// Without loop information, we cannot do any better, so bail now...
if (L == 0) return Unknown;
if (isLoopInvariant(Start, L) && isLoopInvariant(Step, L))
return Linear;
return Unknown;
}
// Create an induction variable for the specified value. If it is a PHI, and
// if it's recognizable, classify it and fill in instance variables.
//
InductionVariable::InductionVariable(PHINode *P, cfg::LoopInfo *LoopInfo) {
InductionType = Unknown; // Assume the worst
Phi = P;
// If the PHI node has more than two predecessors, we don't know how to
// handle it.
//
if (Phi->getNumIncomingValues() != 2) return;
// FIXME: Handle FP induction variables.
if (Phi->getType() == Type::FloatTy || Phi->getType() == Type::DoubleTy)
return;
// If we have loop information, make sure that this PHI node is in the header
// of a loop...
//
const cfg::Loop *L = LoopInfo ? LoopInfo->getLoopFor(Phi->getParent()) : 0;
if (L && L->getHeader() != Phi->getParent())
return;
Value *V1 = Phi->getIncomingValue(0);
Value *V2 = Phi->getIncomingValue(1);
if (L == 0) { // No loop information? Base everything on expression analysis
ExprType E1 = analysis::ClassifyExpression(V1);
ExprType E2 = analysis::ClassifyExpression(V2);
if (E1.ExprTy > E2.ExprTy) // Make E1 be the simpler expression
std::swap(E1, E2);
// E1 must be a constant incoming value, and E2 must be a linear expression
// with respect to the PHI node.
//
if (E1.ExprTy > ExprType::Constant || E2.ExprTy != ExprType::Linear ||
E2.Var != Phi)
return;
// Okay, we have found an induction variable. Save the start and step values
const Type *ETy = Phi->getType();
if (ETy->isPointerType()) ETy = Type::ULongTy;
Start = (Value*)(E1.Offset ? E1.Offset : ConstantInt::get(ETy, 0));
Step = (Value*)(E2.Offset ? E2.Offset : ConstantInt::get(ETy, 0));
} else {
// Okay, at this point, we know that we have loop information...
// Make sure that V1 is the incoming value, and V2 is from the backedge of
// the loop.
if (L->contains(Phi->getIncomingBlock(0))) // Wrong order. Swap now.
std::swap(V1, V2);
Start = V1; // We know that Start has to be loop invariant...
Step = 0;
if (V2 == Phi) { // referencing the PHI directly? Must have zero step
Step = Constant::getNullValue(Phi->getType());
} else if (BinaryOperator *I = dyn_cast<BinaryOperator>(V2)) {
// TODO: This could be much better...
if (I->getOpcode() == Instruction::Add) {
if (I->getOperand(0) == Phi)
Step = I->getOperand(1);
else if (I->getOperand(1) == Phi)
Step = I->getOperand(0);
}
}
if (Step == 0) { // Unrecognized step value...
ExprType StepE = analysis::ClassifyExpression(V2);
if (StepE.ExprTy != ExprType::Linear ||
StepE.Var != Phi) return;
const Type *ETy = Phi->getType();
if (ETy->isPointerType()) ETy = Type::ULongTy;
Step = (Value*)(StepE.Offset ? StepE.Offset : ConstantInt::get(ETy, 0));
} else { // We were able to get a step value, simplify with expr analysis
ExprType StepE = analysis::ClassifyExpression(Step);
if (StepE.ExprTy == ExprType::Linear && StepE.Offset == 0) {
// No offset from variable? Grab the variable
Step = StepE.Var;
} else if (StepE.ExprTy == ExprType::Constant) {
if (StepE.Offset)
Step = (Value*)StepE.Offset;
else
Step = Constant::getNullValue(Step->getType());
const Type *ETy = Phi->getType();
if (ETy->isPointerType()) ETy = Type::ULongTy;
Step = (Value*)(StepE.Offset ? StepE.Offset : ConstantInt::get(ETy,0));
}
}
}
// Classify the induction variable type now...
InductionType = InductionVariable::Classify(Start, Step, L);
}
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