void StraightLineStrengthReduce::factorArrayIndex(Value *ArrayIdx,
const SCEV *Base,
uint64_t ElementSize,
GetElementPtrInst *GEP) {
// At least, ArrayIdx = ArrayIdx *nsw 1.
allocateCandidatesAndFindBasisForGEP(
Base, ConstantInt::get(cast<IntegerType>(ArrayIdx->getType()), 1),
ArrayIdx, ElementSize, GEP);
Value *LHS = nullptr;
ConstantInt *RHS = nullptr;
// One alternative is matching the SCEV of ArrayIdx instead of ArrayIdx
// itself. This would allow us to handle the shl case for free. However,
// matching SCEVs has two issues:
//
// 1. this would complicate rewriting because the rewriting procedure
// would have to translate SCEVs back to IR instructions. This translation
// is difficult when LHS is further evaluated to a composite SCEV.
//
// 2. ScalarEvolution is designed to be control-flow oblivious. It tends
// to strip nsw/nuw flags which are critical for SLSR to trace into
// sext'ed multiplication.
if (match(ArrayIdx, m_NSWMul(m_Value(LHS), m_ConstantInt(RHS)))) {
// SLSR is currently unsafe if i * S may overflow.
// GEP = Base + sext(LHS *nsw RHS) * ElementSize
allocateCandidatesAndFindBasisForGEP(Base, RHS, LHS, ElementSize, GEP);
} else if (match(ArrayIdx, m_NSWShl(m_Value(LHS), m_ConstantInt(RHS)))) {
// GEP = Base + sext(LHS <<nsw RHS) * ElementSize
// = Base + sext(LHS *nsw (1 << RHS)) * ElementSize
APInt One(RHS->getBitWidth(), 1);
ConstantInt *PowerOf2 =
ConstantInt::get(RHS->getContext(), One << RHS->getValue());
allocateCandidatesAndFindBasisForGEP(Base, PowerOf2, LHS, ElementSize, GEP);
}
}
void StraightLineStrengthReduce::allocateCandidatesAndFindBasisForAdd(
Value *LHS, Value *RHS, Instruction *I) {
Value *S = nullptr;
ConstantInt *Idx = nullptr;
if (match(RHS, m_Mul(m_Value(S), m_ConstantInt(Idx)))) {
// I = LHS + RHS = LHS + Idx * S
allocateCandidatesAndFindBasis(Candidate::Add, SE->getSCEV(LHS), Idx, S, I);
} else if (match(RHS, m_Shl(m_Value(S), m_ConstantInt(Idx)))) {
// I = LHS + RHS = LHS + (S << Idx) = LHS + S * (1 << Idx)
APInt One(Idx->getBitWidth(), 1);
Idx = ConstantInt::get(Idx->getContext(), One << Idx->getValue());
allocateCandidatesAndFindBasis(Candidate::Add, SE->getSCEV(LHS), Idx, S, I);
} else {
// At least, I = LHS + 1 * RHS
ConstantInt *One = ConstantInt::get(cast<IntegerType>(I->getType()), 1);
allocateCandidatesAndFindBasis(Candidate::Add, SE->getSCEV(LHS), One, RHS,
I);
}
}
// switchConvert - Convert the switch statement into a binary lookup of
// the case values. The function recursively builds this tree.
// LowerBound and UpperBound are used to keep track of the bounds for Val
// that have already been checked by a block emitted by one of the previous
// calls to switchConvert in the call stack.
BasicBlock *
LowerSwitch::switchConvert(CaseItr Begin, CaseItr End, ConstantInt *LowerBound,
ConstantInt *UpperBound, Value *Val,
BasicBlock *Predecessor, BasicBlock *OrigBlock,
BasicBlock *Default,
const std::vector<IntRange> &UnreachableRanges) {
unsigned Size = End - Begin;
if (Size == 1) {
// Check if the Case Range is perfectly squeezed in between
// already checked Upper and Lower bounds. If it is then we can avoid
// emitting the code that checks if the value actually falls in the range
// because the bounds already tell us so.
if (Begin->Low == LowerBound && Begin->High == UpperBound) {
unsigned NumMergedCases = 0;
if (LowerBound && UpperBound)
NumMergedCases =
UpperBound->getSExtValue() - LowerBound->getSExtValue();
fixPhis(Begin->BB, OrigBlock, Predecessor, NumMergedCases);
return Begin->BB;
}
return newLeafBlock(*Begin, Val, OrigBlock, Default);
}
unsigned Mid = Size / 2;
std::vector<CaseRange> LHS(Begin, Begin + Mid);
DEBUG(dbgs() << "LHS: " << LHS << "\n");
std::vector<CaseRange> RHS(Begin + Mid, End);
DEBUG(dbgs() << "RHS: " << RHS << "\n");
CaseRange &Pivot = *(Begin + Mid);
DEBUG(dbgs() << "Pivot ==> "
<< Pivot.Low->getValue()
<< " -" << Pivot.High->getValue() << "\n");
// NewLowerBound here should never be the integer minimal value.
// This is because it is computed from a case range that is never
// the smallest, so there is always a case range that has at least
// a smaller value.
ConstantInt *NewLowerBound = Pivot.Low;
// Because NewLowerBound is never the smallest representable integer
// it is safe here to subtract one.
ConstantInt *NewUpperBound = ConstantInt::get(NewLowerBound->getContext(),
NewLowerBound->getValue() - 1);
if (!UnreachableRanges.empty()) {
// Check if the gap between LHS's highest and NewLowerBound is unreachable.
int64_t GapLow = LHS.back().High->getSExtValue() + 1;
int64_t GapHigh = NewLowerBound->getSExtValue() - 1;
IntRange Gap = { GapLow, GapHigh };
if (GapHigh >= GapLow && IsInRanges(Gap, UnreachableRanges))
NewUpperBound = LHS.back().High;
}
DEBUG(dbgs() << "LHS Bounds ==> ";
if (LowerBound) {
dbgs() << LowerBound->getSExtValue();
} else {
dbgs() << "NONE";
}
dbgs() << " - " << NewUpperBound->getSExtValue() << "\n";
dbgs() << "RHS Bounds ==> ";
dbgs() << NewLowerBound->getSExtValue() << " - ";
if (UpperBound) {
dbgs() << UpperBound->getSExtValue() << "\n";
} else {
dbgs() << "NONE\n";
});