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Wind SCEV back in time, to Nov 18th. This 'fixes' PR3275, PR3294, PR3295,

Browse Source 
PR3296 and PR3302.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@62160 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky
2009-01-13 09:18:58 +00:00
parent 3ff704fa2b
commit 789558db70
12 changed files with 50 additions and 266 deletions
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241
lib/Analysis/ScalarEvolution.cpp
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@ -112,7 +112,6 @@ char ScalarEvolution::ID = 0;
SCEV::~SCEV() {}
void SCEV::dump() const {
print(cerr);
cerr << '\n';
}
uint32_t SCEV::getBitWidth() const {
@ -325,26 +324,6 @@ const Type *SCEVUDivExpr::getType() const {
return LHS->getType();
}
// SCEVSDivs - Only allow the creation of one SCEVSDivExpr for any particular
// input. Don't use a SCEVHandle here, or else the object will never be
// deleted!
static ManagedStatic<std::map<std::pair<SCEV*, SCEV*>,
SCEVSDivExpr*> > SCEVSDivs;
SCEVSDivExpr::~SCEVSDivExpr() {
SCEVSDivs->erase(std::make_pair(LHS, RHS));
}
void SCEVSDivExpr::print(std::ostream &OS) const {
OS << "(" << *LHS << " /s " << *RHS << ")";
}
const Type *SCEVSDivExpr::getType() const {
return LHS->getType();
}
// SCEVAddRecExprs - Only allow the creation of one SCEVAddRecExpr for any
// particular input. Don't use a SCEVHandle here, or else the object will never
// be deleted!
@ -1130,12 +1109,9 @@ SCEVHandle ScalarEvolution::getMulExpr(std::vector<SCEVHandle> &Ops) {
}
SCEVHandle ScalarEvolution::getUDivExpr(const SCEVHandle &LHS, const SCEVHandle &RHS) {
if (LHS == RHS)
return getIntegerSCEV(1, LHS->getType()); // X udiv X --> 1
if (SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS)) {
if (RHSC->getValue()->equalsInt(1))
return LHS; // X udiv 1 --> X
return LHS; // X udiv 1 --> x
if (SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS)) {
Constant *LHSCV = LHSC->getValue();
@ -1144,34 +1120,13 @@ SCEVHandle ScalarEvolution::getUDivExpr(const SCEVHandle &LHS, const SCEVHandle
}
}
// FIXME: implement folding of (X*4)/4 when we know X*4 doesn't overflow.
SCEVUDivExpr *&Result = (*SCEVUDivs)[std::make_pair(LHS, RHS)];
if (Result == 0) Result = new SCEVUDivExpr(LHS, RHS);
return Result;
}
SCEVHandle ScalarEvolution::getSDivExpr(const SCEVHandle &LHS, const SCEVHandle &RHS) {
if (LHS == RHS)
return getIntegerSCEV(1, LHS->getType()); // X sdiv X --> 1
if (SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS)) {
if (RHSC->getValue()->equalsInt(1))
return LHS; // X sdiv 1 --> X
if (RHSC->getValue()->isAllOnesValue())
return getNegativeSCEV(LHS); // X sdiv -1 --> -X
if (SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS)) {
Constant *LHSCV = LHSC->getValue();
Constant *RHSCV = RHSC->getValue();
return getUnknown(ConstantExpr::getSDiv(LHSCV, RHSCV));
}
}
SCEVSDivExpr *&Result = (*SCEVSDivs)[std::make_pair(LHS, RHS)];
if (Result == 0) Result = new SCEVSDivExpr(LHS, RHS);
return Result;
}
/// SCEVAddRecExpr::get - Get a add recurrence expression for the
/// specified loop. Simplify the expression as much as possible.
@ -1522,7 +1477,7 @@ namespace {
/// specified less-than comparison will execute. If not computable, return
/// UnknownValue. isSigned specifies whether the less-than is signed.
SCEVHandle HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L,
bool isSigned, bool trueWhenEqual);
bool isSigned);
/// getPredecessorWithUniqueSuccessorForBB - Return a predecessor of BB
/// (which may not be an immediate predecessor) which has exactly one
@ -1532,13 +1487,7 @@ namespace {
/// executesAtLeastOnce - Test whether entry to the loop is protected by
/// a conditional between LHS and RHS.
bool executesAtLeastOnce(const Loop *L, bool isSigned, bool trueWhenEqual,
SCEV *LHS, SCEV *RHS);
/// potentialInfiniteLoop - Test whether the loop might jump over the exit value
/// due to wrapping.
bool potentialInfiniteLoop(SCEV *Stride, SCEV *RHS, bool isSigned,
bool trueWhenEqual);
bool executesAtLeastOnce(const Loop *L, bool isSigned, SCEV *LHS, SCEV *RHS);
/// getConstantEvolutionLoopExitValue - If we know that the specified Phi is
/// in the header of its containing loop, we know the loop executes a
@ -1777,7 +1726,7 @@ static uint32_t GetMinTrailingZeros(SCEVHandle S) {
return MinOpRes;
}
// SCEVUDivExpr, SCEVSDivExpr, SCEVUnknown
// SCEVUDivExpr, SCEVUnknown
return 0;
}
@ -1807,9 +1756,6 @@ SCEVHandle ScalarEvolutionsImpl::createSCEV(Value *V) {
case Instruction::UDiv:
return SE.getUDivExpr(getSCEV(U->getOperand(0)),
getSCEV(U->getOperand(1)));
case Instruction::SDiv:
return SE.getSDivExpr(getSCEV(U->getOperand(0)),
getSCEV(U->getOperand(1)));
case Instruction::Sub:
return SE.getMinusSCEV(getSCEV(U->getOperand(0)),
getSCEV(U->getOperand(1)));
@ -1853,7 +1799,7 @@ SCEVHandle ScalarEvolutionsImpl::createSCEV(Value *V) {
break;
case Instruction::LShr:
// Turn logical shift right of a constant into an unsigned divide.
// Turn logical shift right of a constant into a unsigned divide.
if (ConstantInt *SA = dyn_cast<ConstantInt>(U->getOperand(1))) {
uint32_t BitWidth = cast<IntegerType>(V->getType())->getBitWidth();
Constant *X = ConstantInt::get(
@ -2079,46 +2025,24 @@ SCEVHandle ScalarEvolutionsImpl::ComputeIterationCount(const Loop *L) {
break;
}
case ICmpInst::ICMP_SLT: {
SCEVHandle TC = HowManyLessThans(LHS, RHS, L, true, false);
SCEVHandle TC = HowManyLessThans(LHS, RHS, L, true);
if (!isa<SCEVCouldNotCompute>(TC)) return TC;
break;
}
case ICmpInst::ICMP_SGT: {
SCEVHandle TC = HowManyLessThans(SE.getNotSCEV(LHS),
SE.getNotSCEV(RHS), L, true, false);
SE.getNotSCEV(RHS), L, true);
if (!isa<SCEVCouldNotCompute>(TC)) return TC;
break;
}
case ICmpInst::ICMP_ULT: {
SCEVHandle TC = HowManyLessThans(LHS, RHS, L, false, false);
SCEVHandle TC = HowManyLessThans(LHS, RHS, L, false);
if (!isa<SCEVCouldNotCompute>(TC)) return TC;
break;
}
case ICmpInst::ICMP_UGT: {
SCEVHandle TC = HowManyLessThans(SE.getNotSCEV(LHS),
SE.getNotSCEV(RHS), L, false, false);
if (!isa<SCEVCouldNotCompute>(TC)) return TC;
break;
}
case ICmpInst::ICMP_SLE: {
SCEVHandle TC = HowManyLessThans(LHS, RHS, L, true, true);
if (!isa<SCEVCouldNotCompute>(TC)) return TC;
break;
}
case ICmpInst::ICMP_SGE: {
SCEVHandle TC = HowManyLessThans(SE.getNotSCEV(LHS),
SE.getNotSCEV(RHS), L, true, true);
if (!isa<SCEVCouldNotCompute>(TC)) return TC;
break;
}
case ICmpInst::ICMP_ULE: {
SCEVHandle TC = HowManyLessThans(LHS, RHS, L, false, true);
if (!isa<SCEVCouldNotCompute>(TC)) return TC;
break;
}
case ICmpInst::ICMP_UGE: {
SCEVHandle TC = HowManyLessThans(SE.getNotSCEV(LHS),
SE.getNotSCEV(RHS), L, false, true);
SE.getNotSCEV(RHS), L, false);
if (!isa<SCEVCouldNotCompute>(TC)) return TC;
break;
}
@ -2553,26 +2477,16 @@ SCEVHandle ScalarEvolutionsImpl::getSCEVAtScope(SCEV *V, const Loop *L) {
return Comm;
}
if (SCEVUDivExpr *UDiv = dyn_cast<SCEVUDivExpr>(V)) {
SCEVHandle LHS = getSCEVAtScope(UDiv->getLHS(), L);
if (SCEVUDivExpr *Div = dyn_cast<SCEVUDivExpr>(V)) {
SCEVHandle LHS = getSCEVAtScope(Div->getLHS(), L);
if (LHS == UnknownValue) return LHS;
SCEVHandle RHS = getSCEVAtScope(UDiv->getRHS(), L);
SCEVHandle RHS = getSCEVAtScope(Div->getRHS(), L);
if (RHS == UnknownValue) return RHS;
if (LHS == UDiv->getLHS() && RHS == UDiv->getRHS())
return UDiv; // must be loop invariant
if (LHS == Div->getLHS() && RHS == Div->getRHS())
return Div; // must be loop invariant
return SE.getUDivExpr(LHS, RHS);
}
if (SCEVSDivExpr *SDiv = dyn_cast<SCEVSDivExpr>(V)) {
SCEVHandle LHS = getSCEVAtScope(SDiv->getLHS(), L);
if (LHS == UnknownValue) return LHS;
SCEVHandle RHS = getSCEVAtScope(SDiv->getRHS(), L);
if (RHS == UnknownValue) return RHS;
if (LHS == SDiv->getLHS() && RHS == SDiv->getRHS())
return SDiv; // must be loop invariant
return SE.getSDivExpr(LHS, RHS);
}
// If this is a loop recurrence for a loop that does not contain L, then we
// are dealing with the final value computed by the loop.
if (SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(V)) {
@ -2824,7 +2738,6 @@ ScalarEvolutionsImpl::getPredecessorWithUniqueSuccessorForBB(BasicBlock *BB) {
/// executesAtLeastOnce - Test whether entry to the loop is protected by
/// a conditional between LHS and RHS.
bool ScalarEvolutionsImpl::executesAtLeastOnce(const Loop *L, bool isSigned,
bool trueWhenEqual,
SCEV *LHS, SCEV *RHS) {
BasicBlock *Preheader = L->getLoopPreheader();
BasicBlock *PreheaderDest = L->getHeader();
@ -2857,36 +2770,20 @@ bool ScalarEvolutionsImpl::executesAtLeastOnce(const Loop *L, bool isSigned,
switch (Cond) {
case ICmpInst::ICMP_UGT:
if (isSigned || trueWhenEqual) continue;
if (isSigned) continue;
std::swap(PreCondLHS, PreCondRHS);
Cond = ICmpInst::ICMP_ULT;
break;
case ICmpInst::ICMP_SGT:
if (!isSigned || trueWhenEqual) continue;
if (!isSigned) continue;
std::swap(PreCondLHS, PreCondRHS);
Cond = ICmpInst::ICMP_SLT;
break;
case ICmpInst::ICMP_ULT:
if (isSigned || trueWhenEqual) continue;
if (isSigned) continue;
break;
case ICmpInst::ICMP_SLT:
if (!isSigned || trueWhenEqual) continue;
break;
case ICmpInst::ICMP_UGE:
if (isSigned || !trueWhenEqual) continue;
std::swap(PreCondLHS, PreCondRHS);
Cond = ICmpInst::ICMP_ULE;
break;
case ICmpInst::ICMP_SGE:
if (!isSigned || !trueWhenEqual) continue;
std::swap(PreCondLHS, PreCondRHS);
Cond = ICmpInst::ICMP_SLE;
break;
case ICmpInst::ICMP_ULE:
if (isSigned || !trueWhenEqual) continue;
break;
case ICmpInst::ICMP_SLE:
if (!isSigned || !trueWhenEqual) continue;
if (!isSigned) continue;
break;
default:
continue;
@ -2905,47 +2802,11 @@ bool ScalarEvolutionsImpl::executesAtLeastOnce(const Loop *L, bool isSigned,
return false;
}
/// potentialInfiniteLoop - Test whether the loop might jump over the exit value
/// due to wrapping around 2^n.
bool ScalarEvolutionsImpl::potentialInfiniteLoop(SCEV *Stride, SCEV *RHS,
bool isSigned, bool trueWhenEqual) {
// Return true when the distance from RHS to maxint > Stride.
SCEVConstant *SC = dyn_cast<SCEVConstant>(Stride);
if (!SC)
return true;
if (SC->getValue()->isZero())
return true;
if (!trueWhenEqual && SC->getValue()->isOne())
return false;
SCEVConstant *R = dyn_cast<SCEVConstant>(RHS);
if (!R)
return true;
// If negative, it wraps around every iteration, but we don't care about that.
APInt S = SC->getValue()->getValue().abs();
uint32_t Width = R->getValue()->getBitWidth();
APInt Dist = (isSigned ? APInt::getSignedMaxValue(Width)
: APInt::getMaxValue(Width))
- R->getValue()->getValue();
// Because we're looking at distance, we perform an unsigned comparison,
// regardless of the sign of the computation.
if (trueWhenEqual)
return !S.ult(Dist);
else
return !S.ule(Dist);
}
/// HowManyLessThans - Return the number of times a backedge containing the
/// specified less-than comparison will execute. If not computable, return
/// UnknownValue.
SCEVHandle ScalarEvolutionsImpl::
HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L,
bool isSigned, bool trueWhenEqual) {
HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L, bool isSigned) {
// Only handle: "ADDREC < LoopInvariant".
if (!RHS->isLoopInvariant(L)) return UnknownValue;
@ -2954,56 +2815,34 @@ HowManyLessThans(SCEV *LHS, SCEV *RHS, const Loop *L,
return UnknownValue;
if (AddRec->isAffine()) {
SCEVHandle Stride = AddRec->getOperand(1);
if (potentialInfiniteLoop(Stride, RHS, isSigned, trueWhenEqual))
// FORNOW: We only support unit strides.
SCEVHandle One = SE.getIntegerSCEV(1, RHS->getType());
if (AddRec->getOperand(1) != One)
return UnknownValue;
// We don't handle this correctly at the moment. The problem is that when
// the stride is negative, we're not counting how many times 'less-than' is
// true as we approach it, we're counting how far away we are from wrapping
// around the backside.
if (isSigned &&
cast<SCEVConstant>(Stride)->getValue()->getValue().isNegative())
return UnknownValue;
// We know the LHS is of the form {n,+,s} and the RHS is some loop-invariant
// m. So, we count the number of iterations in which {n,+,s} < m is true.
// Note that we cannot simply return max(m-n,0)/s because it's not safe to
// We know the LHS is of the form {n,+,1} and the RHS is some loop-invariant
// m. So, we count the number of iterations in which {n,+,1} < m is true.
// Note that we cannot simply return max(m-n,0) because it's not safe to
// treat m-n as signed nor unsigned due to overflow possibility.
//
// Assuming that the loop will run at least once, we know that it will
// run (m-n)/s times.
// First, we get the value of the LHS in the first iteration: n
SCEVHandle Start = AddRec->getOperand(0);
SCEVHandle One = SE.getIntegerSCEV(1, RHS->getType());
if (executesAtLeastOnce(L, isSigned,
SE.getMinusSCEV(AddRec->getOperand(0), One), RHS)) {
// Since we know that the condition is true in order to enter the loop,
// we know that it will run exactly m-n times.
return SE.getMinusSCEV(RHS, Start);
} else {
// Then, we get the value of the LHS in the first iteration in which the
// above condition doesn't hold. This equals to max(m,n).
SCEVHandle End = isSigned ? SE.getSMaxExpr(RHS, Start)
: SE.getUMaxExpr(RHS, Start);
// If the expression is less-than-or-equal to, we need to extend the
// loop by one iteration.
//
// The loop won't actually run (m-n)/s times because the loop iterations
// might not divide cleanly. For example, if you have {2,+,5} u< 10 the
// division would equal one, but the loop runs twice putting the
// induction variable at 12.
SCEVHandle End = SE.getAddExpr(RHS, Stride);
if (!trueWhenEqual)
End = SE.getMinusSCEV(End, One);
if (!executesAtLeastOnce(L, isSigned, trueWhenEqual,
SE.getMinusSCEV(Start, One), RHS)) {
// If not, we get the value of the LHS in the first iteration in which
// the above condition doesn't hold. This equals to max(m,n).
End = isSigned ? SE.getSMaxExpr(End, Start)
: SE.getUMaxExpr(End, Start);
// Finally, we subtract these two values to get the number of times the
// backedge is executed: max(m,n)-n.
return SE.getMinusSCEV(End, Start);
}
// Finally, we subtract these two values to get the number of times the
// backedge is executed: (max(m,n)-n)/s.
//
// Note that a trip count is always positive. Using SDiv here produces
// wrong answers when Start < End.
return SE.getUDivExpr(SE.getMinusSCEV(End, Start), Stride);
}
return UnknownValue;