mirror of
https://github.com/RPCS3/llvm-mirror.git
synced 2024-10-30 07:22:55 +01:00
302 lines
10 KiB
C++
302 lines
10 KiB
C++
//===- 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/BasicBlock.h"
|
|
#include "llvm/iPHINode.h"
|
|
#include "llvm/iOperators.h"
|
|
#include "llvm/iTerminators.h"
|
|
#include "llvm/Type.h"
|
|
#include "llvm/Constants.h"
|
|
#include "llvm/Support/CFG.h"
|
|
#include "llvm/Assembly/Writer.h"
|
|
#include "Support/Statistic.h"
|
|
|
|
static bool isLoopInvariant(const Value *V, const 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 Loop *L) {
|
|
// Check for cannonical and simple linear expressions now...
|
|
if (const ConstantInt *CStart = dyn_cast<ConstantInt>(Start))
|
|
if (const 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, LoopInfo *LoopInfo): End(0) {
|
|
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 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 = ClassifyExpression(V1);
|
|
ExprType E2 = 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 (isa<PointerType>(ETy)) 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 = ClassifyExpression(V2);
|
|
if (StepE.ExprTy != ExprType::Linear ||
|
|
StepE.Var != Phi) return;
|
|
|
|
const Type *ETy = Phi->getType();
|
|
if (isa<PointerType>(ETy)) 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 = 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 (isa<PointerType>(ETy)) 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);
|
|
}
|
|
|
|
|
|
Value* InductionVariable::getExecutionCount(LoopInfo *LoopInfo) {
|
|
DEBUG(std::cerr << "entering getExecutionCount\n");
|
|
|
|
// Don't recompute if already available
|
|
if (End) {
|
|
DEBUG(std::cerr << "returning cached End value.\n");
|
|
return End;
|
|
}
|
|
|
|
const Loop *L = LoopInfo ? LoopInfo->getLoopFor(Phi->getParent()) : 0;
|
|
if (!L) {
|
|
DEBUG(std::cerr << "null loop. oops\n");
|
|
return NULL;
|
|
}
|
|
|
|
// >1 backedge => cannot predict number of iterations
|
|
if (Phi->getNumIncomingValues() != 2) {
|
|
DEBUG(std::cerr << ">2 incoming values. oops\n");
|
|
return NULL;
|
|
}
|
|
|
|
// Find final node: predecesor of the loop header that's also an exit
|
|
BasicBlock *terminator = 0;
|
|
BasicBlock *header = L->getHeader();
|
|
for (pred_iterator PI = pred_begin(header), PE = pred_end(header);
|
|
PI != PE; ++PI) {
|
|
if (L->isLoopExit(*PI)) {
|
|
terminator = *PI;
|
|
break;
|
|
}
|
|
}
|
|
|
|
// Break in the loop => cannot predict number of iterations
|
|
// break: any block which is an exit node whose successor is not in loop,
|
|
// and this block is not marked as the terminator
|
|
//
|
|
const std::vector<BasicBlock*> &blocks = L->getBlocks();
|
|
for (std::vector<BasicBlock*>::const_iterator i = blocks.begin(), e = blocks.end();
|
|
i != e; ++i) {
|
|
if (L->isLoopExit(*i) && (*i != terminator)) {
|
|
for (succ_iterator SI = succ_begin(*i), SE = succ_end(*i); SI != SE; ++SI) {
|
|
if (! L->contains(*SI)) {
|
|
DEBUG(std::cerr << "break found in loop");
|
|
return NULL;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
BranchInst *B = dyn_cast<BranchInst>(terminator->getTerminator());
|
|
if (!B) {
|
|
// this really should not happen
|
|
DEBUG(std::cerr << "no terminator instruction!");
|
|
return NULL;
|
|
}
|
|
SetCondInst *SCI = dyn_cast<SetCondInst>(B->getCondition());
|
|
|
|
if (SCI && InductionType == Cannonical) {
|
|
DEBUG(std::cerr << "sci:" << *SCI);
|
|
Value *condVal0 = SCI->getOperand(0);
|
|
Value *condVal1 = SCI->getOperand(1);
|
|
Value *indVar = 0;
|
|
|
|
// the induction variable is the one coming from the backedge
|
|
if (L->contains(Phi->getIncomingBlock(0))) {
|
|
indVar = Phi->getIncomingValue(0);
|
|
} else {
|
|
indVar = Phi->getIncomingValue(1);
|
|
}
|
|
|
|
// check to see if indVar is one of the parameters in SCI
|
|
// and if the other is loop-invariant, it is the UB
|
|
if (indVar == condVal0) {
|
|
if (isLoopInvariant(condVal1, L)) {
|
|
End = condVal1;
|
|
} else {
|
|
DEBUG(std::cerr << "not loop invariant 1\n");
|
|
}
|
|
} else if (indVar == condVal1) {
|
|
if (isLoopInvariant(condVal0, L)) {
|
|
End = condVal0;
|
|
} else {
|
|
DEBUG(std::cerr << "not loop invariant 0\n");
|
|
}
|
|
}
|
|
|
|
if (End) {
|
|
switch (SCI->getOpcode()) {
|
|
case Instruction::SetLT:
|
|
case Instruction::SetNE: break; // already done
|
|
case Instruction::SetLE: {
|
|
// if compared to a constant int N, then predict N+1 iterations
|
|
if (ConstantSInt *ubSigned = dyn_cast<ConstantSInt>(End)) {
|
|
End = ConstantSInt::get(ubSigned->getType(), ubSigned->getValue()+1);
|
|
DEBUG(std::cerr << "signed int constant\n");
|
|
} else if (ConstantUInt *ubUnsigned = dyn_cast<ConstantUInt>(End)) {
|
|
End = ConstantUInt::get(ubUnsigned->getType(), ubUnsigned->getValue()+1);
|
|
DEBUG(std::cerr << "unsigned int constant\n");
|
|
} else {
|
|
DEBUG(std::cerr << "symbolic bound\n");
|
|
//End = NULL;
|
|
// new expression N+1
|
|
End = BinaryOperator::create(Instruction::Add, End,
|
|
ConstantUInt::get(ubUnsigned->getType(), 1));
|
|
}
|
|
break;
|
|
}
|
|
default: End = NULL; // cannot predict
|
|
}
|
|
}
|
|
return End;
|
|
} else {
|
|
DEBUG(std::cerr << "SCI null or non-cannonical ind var\n");
|
|
}
|
|
return NULL;
|
|
}
|
|
|
|
|
|
void InductionVariable::print(std::ostream &o) const {
|
|
switch (InductionType) {
|
|
case InductionVariable::Cannonical: o << "Cannonical "; break;
|
|
case InductionVariable::SimpleLinear: o << "SimpleLinear "; break;
|
|
case InductionVariable::Linear: o << "Linear "; break;
|
|
case InductionVariable::Unknown: o << "Unrecognized "; break;
|
|
}
|
|
o << "Induction Variable: ";
|
|
if (Phi) {
|
|
WriteAsOperand(o, Phi);
|
|
o << ":\n" << Phi;
|
|
} else {
|
|
o << "\n";
|
|
}
|
|
if (InductionType == InductionVariable::Unknown) return;
|
|
|
|
o << " Start = "; WriteAsOperand(o, Start);
|
|
o << " Step = " ; WriteAsOperand(o, Step);
|
|
if (End) {
|
|
o << " End = " ; WriteAsOperand(o, End);
|
|
}
|
|
o << "\n";
|
|
}
|