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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2323 91177308-0d34-0410-b5e6-96231b3b80d8
157 lines
5.6 KiB
C++
157 lines
5.6 KiB
C++
//===- llvm/Analysis/InductionVariable.h - Induction variable ----*- C++ -*--=//
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//
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// This interface is used to identify and classify induction variables that
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// exist in the program. Induction variables must contain a PHI node that
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// exists in a loop header. Because of this, they are identified an managed by
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// this PHI node.
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//
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// Induction variables are classified into a type. Knowing that an induction
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// variable is of a specific type can constrain the values of the start and
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// step. For example, a SimpleLinear induction variable must have a start and
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// step values that are constants.
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//
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// Induction variables can be created with or without loop information. If no
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// loop information is available, induction variables cannot be recognized to be
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// more than SimpleLinear variables.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/InductionVariable.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/Expressions.h"
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#include "llvm/iPHINode.h"
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#include "llvm/InstrTypes.h"
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#include "llvm/Type.h"
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#include "llvm/ConstantVals.h"
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using analysis::ExprType;
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static bool isLoopInvariant(const Value *V, const cfg::Loop *L) {
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if (isa<Constant>(V) || isa<Argument>(V) || isa<GlobalValue>(V))
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return true;
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const Instruction *I = cast<Instruction>(V);
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const BasicBlock *BB = I->getParent();
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return !L->contains(BB);
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}
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enum InductionVariable::iType
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InductionVariable::Classify(const Value *Start, const Value *Step,
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const cfg::Loop *L = 0) {
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// Check for cannonical and simple linear expressions now...
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if (ConstantInt *CStart = dyn_cast<ConstantInt>(Start))
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if (ConstantInt *CStep = dyn_cast<ConstantInt>(Step)) {
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if (CStart->equalsInt(0) && CStep->equalsInt(1))
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return Cannonical;
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else
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return SimpleLinear;
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}
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// Without loop information, we cannot do any better, so bail now...
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if (L == 0) return Unknown;
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if (isLoopInvariant(Start, L) && isLoopInvariant(Step, L))
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return Linear;
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return Unknown;
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}
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// Create an induction variable for the specified value. If it is a PHI, and
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// if it's recognizable, classify it and fill in instance variables.
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//
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InductionVariable::InductionVariable(PHINode *P, cfg::LoopInfo *LoopInfo) {
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InductionType = Unknown; // Assume the worst
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Phi = P;
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// If the PHI node has more than two predecessors, we don't know how to
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// handle it.
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//
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if (Phi->getNumIncomingValues() != 2) return;
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// FIXME: Handle FP induction variables.
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if (Phi->getType() == Type::FloatTy || Phi->getType() == Type::DoubleTy)
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return;
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// If we have loop information, make sure that this PHI node is in the header
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// of a loop...
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//
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const cfg::Loop *L = LoopInfo ? LoopInfo->getLoopFor(Phi->getParent()) : 0;
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if (L && L->getHeader() != Phi->getParent())
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return;
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Value *V1 = Phi->getIncomingValue(0);
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Value *V2 = Phi->getIncomingValue(1);
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if (L == 0) { // No loop information? Base everything on expression analysis
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ExprType E1 = analysis::ClassifyExpression(V1);
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ExprType E2 = analysis::ClassifyExpression(V2);
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if (E1.ExprTy > E2.ExprTy) // Make E1 be the simpler expression
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std::swap(E1, E2);
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// E1 must be a constant incoming value, and E2 must be a linear expression
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// with respect to the PHI node.
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//
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if (E1.ExprTy > ExprType::Constant || E2.ExprTy != ExprType::Linear ||
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E2.Var != Phi)
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return;
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// Okay, we have found an induction variable. Save the start and step values
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const Type *ETy = Phi->getType();
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if (ETy->isPointerType()) ETy = Type::ULongTy;
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Start = (Value*)(E1.Offset ? E1.Offset : ConstantInt::get(ETy, 0));
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Step = (Value*)(E2.Offset ? E2.Offset : ConstantInt::get(ETy, 0));
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} else {
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// Okay, at this point, we know that we have loop information...
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// Make sure that V1 is the incoming value, and V2 is from the backedge of
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// the loop.
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if (L->contains(Phi->getIncomingBlock(0))) // Wrong order. Swap now.
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std::swap(V1, V2);
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Start = V1; // We know that Start has to be loop invariant...
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Step = 0;
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if (V2 == Phi) { // referencing the PHI directly? Must have zero step
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Step = Constant::getNullValue(Phi->getType());
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} else if (BinaryOperator *I = dyn_cast<BinaryOperator>(V2)) {
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// TODO: This could be much better...
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if (I->getOpcode() == Instruction::Add) {
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if (I->getOperand(0) == Phi)
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Step = I->getOperand(1);
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else if (I->getOperand(1) == Phi)
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Step = I->getOperand(0);
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}
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}
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if (Step == 0) { // Unrecognized step value...
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ExprType StepE = analysis::ClassifyExpression(V2);
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if (StepE.ExprTy != ExprType::Linear ||
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StepE.Var != Phi) return;
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const Type *ETy = Phi->getType();
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if (ETy->isPointerType()) ETy = Type::ULongTy;
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Step = (Value*)(StepE.Offset ? StepE.Offset : ConstantInt::get(ETy, 0));
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} else { // We were able to get a step value, simplify with expr analysis
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ExprType StepE = analysis::ClassifyExpression(Step);
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if (StepE.ExprTy == ExprType::Linear && StepE.Offset == 0) {
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// No offset from variable? Grab the variable
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Step = StepE.Var;
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} else if (StepE.ExprTy == ExprType::Constant) {
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if (StepE.Offset)
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Step = (Value*)StepE.Offset;
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else
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Step = Constant::getNullValue(Step->getType());
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const Type *ETy = Phi->getType();
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if (ETy->isPointerType()) ETy = Type::ULongTy;
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Step = (Value*)(StepE.Offset ? StepE.Offset : ConstantInt::get(ETy,0));
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}
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}
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}
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// Classify the induction variable type now...
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InductionType = InductionVariable::Classify(Start, Step, L);
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}
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