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SCEV: Added a data structure for storing not-taken info per loop

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exit. Added an interfaces for querying either the loop's exact/max
backedge taken count or a specific loop exit's not-taken count.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@136100 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick 2011-07-26 17:19:55 +00:00
parent b08904093a
commit 5116ff671f
2 changed files with 329 additions and 182 deletions
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172
include/llvm/Analysis/ScalarEvolution.h
View File

@ -241,31 +241,93 @@ namespace llvm {
///
ValueExprMapType ValueExprMap;
/// ExitLimit - Information about the number of loop iterations for
/// which a loop exit's branch condition evaluates to the not-taken path.
/// This is a temporary pair of exact and max expressions that are
/// eventually summarized in ExitNotTakenInfo and BackedgeTakenInfo.
struct ExitLimit {
const SCEV *Exact;
const SCEV *Max;
/*implicit*/ ExitLimit(const SCEV *E) : Exact(E), Max(E) {}
ExitLimit(const SCEV *E, const SCEV *M) : Exact(E), Max(M) {}
/// hasAnyInfo - Test whether this ExitLimit contains any computed
/// information, or whether it's all SCEVCouldNotCompute values.
bool hasAnyInfo() const {
return !isa<SCEVCouldNotCompute>(Exact) ||
!isa<SCEVCouldNotCompute>(Max);
}
};
/// ExitNotTakenInfo - Information about the number of times a particular
/// loop exit may be reached before exiting the loop.
struct ExitNotTakenInfo {
BasicBlock *ExitBlock;
const SCEV *ExactNotTaken;
PointerIntPair<ExitNotTakenInfo*, 1> NextExit;
ExitNotTakenInfo() : ExitBlock(0), ExactNotTaken(0) {}
/// isCompleteList - Return true if all loop exits are computable.
bool isCompleteList() const {
return NextExit.getInt() == 0;
}
void setIncomplete() { NextExit.setInt(1); }
/// getNextExit - Return a pointer to the next exit's not-taken info.
ExitNotTakenInfo *getNextExit() const {
return NextExit.getPointer();
}
void setNextExit(ExitNotTakenInfo *ENT) { NextExit.setPointer(ENT); }
};
/// BackedgeTakenInfo - Information about the backedge-taken count
/// of a loop. This currently includes an exact count and a maximum count.
///
struct BackedgeTakenInfo {
/// Exact - An expression indicating the exact backedge-taken count of
/// the loop if it is known, or a SCEVCouldNotCompute otherwise.
const SCEV *Exact;
class BackedgeTakenInfo {
/// ExitNotTaken - A list of computable exits and their not-taken counts.
/// Loops almost never have more than one computable exit.
ExitNotTakenInfo ExitNotTaken;
/// Max - An expression indicating the least maximum backedge-taken
/// count of the loop that is known, or a SCEVCouldNotCompute.
const SCEV *Max;
/*implicit*/ BackedgeTakenInfo(const SCEV *exact) :
Exact(exact), Max(exact) {}
public:
BackedgeTakenInfo() : Max(0) {}
BackedgeTakenInfo(const SCEV *exact, const SCEV *max) :
Exact(exact), Max(max) {}
/// Initialize BackedgeTakenInfo from a list of exact exit counts.
BackedgeTakenInfo(
SmallVectorImpl< std::pair<BasicBlock *, const SCEV *> > &ExitCounts,
bool Complete, const SCEV *MaxCount);
/// hasAnyInfo - Test whether this BackedgeTakenInfo contains any
/// computed information, or whether it's all SCEVCouldNotCompute
/// values.
bool hasAnyInfo() const {
return !isa<SCEVCouldNotCompute>(Exact) ||
!isa<SCEVCouldNotCompute>(Max);
return ExitNotTaken.ExitBlock || !isa<SCEVCouldNotCompute>(Max);
}
/// getExact - Return an expression indicating the exact backedge-taken
/// count of the loop if it is known, or SCEVCouldNotCompute
/// otherwise. This is the number of times the loop header can be
/// guaranteed to execute, minus one.
const SCEV *getExact(ScalarEvolution *SE) const;
/// getExact - Return the number of times this loop exit may fall through
/// to the back edge. The loop is guaranteed not to exit via this block
/// before this number of iterations, but may exit via another block.
const SCEV *getExact(BasicBlock *ExitBlock, ScalarEvolution *SE) const;
/// getMax - Get the max backedge taken count for the loop.
const SCEV *getMax(ScalarEvolution *SE) const;
/// clear - Invalidate this result and free associated memory.
void clear();
};
/// BackedgeTakenCounts - Cache the backedge-taken count of the loops for
@ -365,64 +427,59 @@ namespace llvm {
/// loop will iterate.
BackedgeTakenInfo ComputeBackedgeTakenCount(const Loop *L);
/// ComputeBackedgeTakenCountFromExit - Compute the number of times the
/// backedge of the specified loop will execute if it exits via the
/// specified block.
BackedgeTakenInfo ComputeBackedgeTakenCountFromExit(const Loop *L,
BasicBlock *ExitingBlock);
/// ComputeExitLimit - Compute the number of times the backedge of the
/// specified loop will execute if it exits via the specified block.
ExitLimit ComputeExitLimit(const Loop *L, BasicBlock *ExitingBlock);
/// ComputeBackedgeTakenCountFromExitCond - Compute the number of times the
/// backedge of the specified loop will execute if its exit condition
/// were a conditional branch of ExitCond, TBB, and FBB.
BackedgeTakenInfo
ComputeBackedgeTakenCountFromExitCond(const Loop *L,
Value *ExitCond,
BasicBlock *TBB,
BasicBlock *FBB);
/// ComputeExitLimitFromCond - Compute the number of times the backedge of
/// the specified loop will execute if its exit condition were a conditional
/// branch of ExitCond, TBB, and FBB.
ExitLimit ComputeExitLimitFromCond(const Loop *L,
Value *ExitCond,
BasicBlock *TBB,
BasicBlock *FBB);
/// ComputeBackedgeTakenCountFromExitCondICmp - Compute the number of
/// times the backedge of the specified loop will execute if its exit
/// condition were a conditional branch of the ICmpInst ExitCond, TBB,
/// and FBB.
BackedgeTakenInfo
ComputeBackedgeTakenCountFromExitCondICmp(const Loop *L,
ICmpInst *ExitCond,
BasicBlock *TBB,
BasicBlock *FBB);
/// ComputeExitLimitFromICmp - Compute the number of times the backedge of
/// the specified loop will execute if its exit condition were a conditional
/// branch of the ICmpInst ExitCond, TBB, and FBB.
ExitLimit ComputeExitLimitFromICmp(const Loop *L,
ICmpInst *ExitCond,
BasicBlock *TBB,
BasicBlock *FBB);
/// ComputeLoadConstantCompareBackedgeTakenCount - Given an exit condition
/// ComputeLoadConstantCompareExitLimit - Given an exit condition
/// of 'icmp op load X, cst', try to see if we can compute the
/// backedge-taken count.
BackedgeTakenInfo
ComputeLoadConstantCompareBackedgeTakenCount(LoadInst *LI,
Constant *RHS,
const Loop *L,
ICmpInst::Predicate p);
ExitLimit ComputeLoadConstantCompareExitLimit(LoadInst *LI,
Constant *RHS,
const Loop *L,
ICmpInst::Predicate p);
/// ComputeBackedgeTakenCountExhaustively - If the loop is known to execute
/// a constant number of times (the condition evolves only from constants),
/// ComputeExitCountExhaustively - If the loop is known to execute a
/// constant number of times (the condition evolves only from constants),
/// try to evaluate a few iterations of the loop until we get the exit
/// condition gets a value of ExitWhen (true or false). If we cannot
/// evaluate the backedge-taken count of the loop, return CouldNotCompute.
const SCEV *ComputeBackedgeTakenCountExhaustively(const Loop *L,
Value *Cond,
bool ExitWhen);
/// evaluate the exit count of the loop, return CouldNotCompute.
const SCEV *ComputeExitCountExhaustively(const Loop *L,
Value *Cond,
bool ExitWhen);
/// HowFarToZero - Return the number of times a backedge comparing the
/// specified value to zero will execute. If not computable, return
/// HowFarToZero - Return the number of times an exit condition comparing
/// the specified value to zero will execute. If not computable, return
/// CouldNotCompute.
BackedgeTakenInfo HowFarToZero(const SCEV *V, const Loop *L);
ExitLimit HowFarToZero(const SCEV *V, const Loop *L);
/// HowFarToNonZero - Return the number of times a backedge checking the
/// specified value for nonzero will execute. If not computable, return
/// HowFarToNonZero - Return the number of times an exit condition checking
/// the specified value for nonzero will execute. If not computable, return
/// CouldNotCompute.
BackedgeTakenInfo HowFarToNonZero(const SCEV *V, const Loop *L);
ExitLimit HowFarToNonZero(const SCEV *V, const Loop *L);
/// HowManyLessThans - Return the number of times a backedge containing the
/// specified less-than comparison will execute. If not computable, return
/// CouldNotCompute. isSigned specifies whether the less-than is signed.
BackedgeTakenInfo HowManyLessThans(const SCEV *LHS, const SCEV *RHS,
const Loop *L, bool isSigned);
/// HowManyLessThans - Return the number of times an exit condition
/// containing the specified less-than comparison will execute. If not
/// computable, return CouldNotCompute. isSigned specifies whether the
/// less-than is signed.
ExitLimit HowManyLessThans(const SCEV *LHS, const SCEV *RHS,
const Loop *L, bool isSigned);
/// getPredecessorWithUniqueSuccessorForBB - Return a predecessor of BB
/// (which may not be an immediate predecessor) which has exactly one
@ -653,6 +710,11 @@ namespace llvm {
bool isLoopBackedgeGuardedByCond(const Loop *L, ICmpInst::Predicate Pred,
const SCEV *LHS, const SCEV *RHS);
// getExitCount - Get the expression for the number of loop iterations for
// which this loop is guaranteed not to exit via ExitBlock. Otherwise return
// SCEVCouldNotCompute.
const SCEV *getExitCount(Loop *L, BasicBlock *ExitBlock);
/// getBackedgeTakenCount - If the specified loop has a predictable
/// backedge-taken count, return it, otherwise return a SCEVCouldNotCompute
/// object. The backedge-taken count is the number of times the loop header

339
lib/Analysis/ScalarEvolution.cpp
View File

@ -3813,6 +3813,13 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) {
// Iteration Count Computation Code
//
// getExitCount - Get the expression for the number of loop iterations for which
// this loop is guaranteed not to exit via ExitBlock. Otherwise return
// SCEVCouldNotCompute.
const SCEV *ScalarEvolution::getExitCount(Loop *L, BasicBlock *ExitBlock) {
return getBackedgeTakenInfo(L).getExact(ExitBlock, this);
}
/// getBackedgeTakenCount - If the specified loop has a predictable
/// backedge-taken count, return it, otherwise return a SCEVCouldNotCompute
/// object. The backedge-taken count is the number of times the loop header
@ -3825,14 +3832,14 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) {
/// hasLoopInvariantBackedgeTakenCount).
///
const SCEV *ScalarEvolution::getBackedgeTakenCount(const Loop *L) {
return getBackedgeTakenInfo(L).Exact;
return getBackedgeTakenInfo(L).getExact(this);
}
/// getMaxBackedgeTakenCount - Similar to getBackedgeTakenCount, except
/// return the least SCEV value that is known never to be less than the
/// actual backedge taken count.
const SCEV *ScalarEvolution::getMaxBackedgeTakenCount(const Loop *L) {
return getBackedgeTakenInfo(L).Max;
return getBackedgeTakenInfo(L).getMax(this);
}
/// PushLoopPHIs - Push PHI nodes in the header of the given loop
@ -3849,33 +3856,31 @@ PushLoopPHIs(const Loop *L, SmallVectorImpl<Instruction *> &Worklist) {
const ScalarEvolution::BackedgeTakenInfo &
ScalarEvolution::getBackedgeTakenInfo(const Loop *L) {
// Initially insert a CouldNotCompute for this loop. If the insertion
// Initially insert an invalid entry for this loop. If the insertion
// succeeds, proceed to actually compute a backedge-taken count and
// update the value. The temporary CouldNotCompute value tells SCEV
// code elsewhere that it shouldn't attempt to request a new
// backedge-taken count, which could result in infinite recursion.
std::pair<DenseMap<const Loop *, BackedgeTakenInfo>::iterator, bool> Pair =
BackedgeTakenCounts.insert(std::make_pair(L, getCouldNotCompute()));
BackedgeTakenCounts.insert(std::make_pair(L, BackedgeTakenInfo()));
if (!Pair.second)
return Pair.first->second;
BackedgeTakenInfo Result = getCouldNotCompute();
BackedgeTakenInfo Computed = ComputeBackedgeTakenCount(L);
if (Computed.Exact != getCouldNotCompute()) {
assert(isLoopInvariant(Computed.Exact, L) &&
isLoopInvariant(Computed.Max, L) &&
// ComputeBackedgeTakenCount may allocate memory for its result. Inserting it
// into the BackedgeTakenCounts map transfers ownership. Otherwise, the result
// must be cleared in this scope.
BackedgeTakenInfo Result = ComputeBackedgeTakenCount(L);
if (Result.getExact(this) != getCouldNotCompute()) {
assert(isLoopInvariant(Result.getExact(this), L) &&
isLoopInvariant(Result.getMax(this), L) &&
"Computed backedge-taken count isn't loop invariant for loop!");
++NumTripCountsComputed;
// Update the value in the map.
Result = Computed;
} else {
if (Computed.Max != getCouldNotCompute())
// Update the value in the map.
Result = Computed;
if (isa<PHINode>(L->getHeader()->begin()))
// Only count loops that have phi nodes as not being computable.
++NumTripCountsNotComputed;
}
else if (Result.getMax(this) == getCouldNotCompute() &&
isa<PHINode>(L->getHeader()->begin())) {
// Only count loops that have phi nodes as not being computable.
++NumTripCountsNotComputed;
}
// Now that we know more about the trip count for this loop, forget any
@ -3883,7 +3888,7 @@ ScalarEvolution::getBackedgeTakenInfo(const Loop *L) {
// conservative estimates made without the benefit of trip count
// information. This is similar to the code in forgetLoop, except that
// it handles SCEVUnknown PHI nodes specially.
if (Computed.hasAnyInfo()) {
if (Result.hasAnyInfo()) {
SmallVector<Instruction *, 16> Worklist;
PushLoopPHIs(L, Worklist);
@ -3928,7 +3933,12 @@ ScalarEvolution::getBackedgeTakenInfo(const Loop *L) {
/// compute a trip count, or if the loop is deleted.
void ScalarEvolution::forgetLoop(const Loop *L) {
// Drop any stored trip count value.
BackedgeTakenCounts.erase(L);
DenseMap<const Loop*, BackedgeTakenInfo>::iterator BTCPos =
BackedgeTakenCounts.find(L);
if (BTCPos != BackedgeTakenCounts.end()) {
BTCPos->second.clear();
BackedgeTakenCounts.erase(BTCPos);
}
// Drop information about expressions based on loop-header PHIs.
SmallVector<Instruction *, 16> Worklist;
@ -3984,6 +3994,84 @@ void ScalarEvolution::forgetValue(Value *V) {
}
}
/// getExact - Get the exact loop backedge taken count considering all loop
/// exits. If all exits are computable, this is the minimum computed count.
const SCEV *
ScalarEvolution::BackedgeTakenInfo::getExact(ScalarEvolution *SE) const {
// If any exits were not computable, the loop is not computable.
if (!ExitNotTaken.isCompleteList()) return SE->getCouldNotCompute();
// We need at least one computable exit.
if (!ExitNotTaken.ExitBlock) return SE->getCouldNotCompute();
assert(ExitNotTaken.ExactNotTaken && "uninitialized not-taken info");
const SCEV *BECount = 0;
for (const ExitNotTakenInfo *ENT = &ExitNotTaken;
ENT != 0; ENT = ENT->getNextExit()) {
assert(ENT->ExactNotTaken != SE->getCouldNotCompute() && "bad exit SCEV");
if (!BECount)
BECount = ENT->ExactNotTaken;
else
BECount = SE->getUMinFromMismatchedTypes(BECount, ENT->ExactNotTaken);
}
return BECount;
}
/// getExact - Get the exact not taken count for this loop exit.
const SCEV *
ScalarEvolution::BackedgeTakenInfo::getExact(BasicBlock *ExitBlock,
ScalarEvolution *SE) const {
for (const ExitNotTakenInfo *ENT = &ExitNotTaken;
ENT != 0; ENT = ENT->getNextExit()) {
if (ENT->ExitBlock == ExitBlock)
return ENT->ExactNotTaken;
}
return SE->getCouldNotCompute();
}
/// getMax - Get the max backedge taken count for the loop.
const SCEV *
ScalarEvolution::BackedgeTakenInfo::getMax(ScalarEvolution *SE) const {
return Max ? Max : SE->getCouldNotCompute();
}
/// Allocate memory for BackedgeTakenInfo and copy the not-taken count of each
/// computable exit into a persistent ExitNotTakenInfo array.
ScalarEvolution::BackedgeTakenInfo::BackedgeTakenInfo(
SmallVectorImpl< std::pair<BasicBlock *, const SCEV *> > &ExitCounts,
bool Complete, const SCEV *MaxCount) : Max(MaxCount) {
if (!Complete)
ExitNotTaken.setIncomplete();
unsigned NumExits = ExitCounts.size();
if (NumExits == 0) return;
ExitNotTaken.ExitBlock = ExitCounts[0].first;
ExitNotTaken.ExactNotTaken = ExitCounts[0].second;
if (NumExits == 1) return;
// Handle the rare case of multiple computable exits.
ExitNotTakenInfo *ENT = new ExitNotTakenInfo[NumExits-1];
ExitNotTakenInfo *PrevENT = &ExitNotTaken;
for (unsigned i = 1; i < NumExits; ++i, PrevENT = ENT, ++ENT) {
PrevENT->setNextExit(ENT);
ENT->ExitBlock = ExitCounts[i].first;
ENT->ExactNotTaken = ExitCounts[i].second;
}
}
/// clear - Invalidate this result and free the ExitNotTakenInfo array.
void ScalarEvolution::BackedgeTakenInfo::clear() {
ExitNotTaken.ExitBlock = 0;
ExitNotTaken.ExactNotTaken = 0;
delete[] ExitNotTaken.getNextExit();
}
/// ComputeBackedgeTakenCount - Compute the number of times the backedge
/// of the specified loop will execute.
ScalarEvolution::BackedgeTakenInfo
@ -3992,38 +4080,31 @@ ScalarEvolution::ComputeBackedgeTakenCount(const Loop *L) {
L->getExitingBlocks(ExitingBlocks);
// Examine all exits and pick the most conservative values.
const SCEV *BECount = getCouldNotCompute();
const SCEV *MaxBECount = getCouldNotCompute();
bool CouldNotComputeBECount = false;
bool CouldComputeBECount = true;
SmallVector<std::pair<BasicBlock *, const SCEV *>, 4> ExitCounts;
for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
BackedgeTakenInfo NewBTI =
ComputeBackedgeTakenCountFromExit(L, ExitingBlocks[i]);
if (NewBTI.Exact == getCouldNotCompute()) {
ExitLimit EL = ComputeExitLimit(L, ExitingBlocks[i]);
if (EL.Exact == getCouldNotCompute())
// We couldn't compute an exact value for this exit, so
// we won't be able to compute an exact value for the loop.
CouldNotComputeBECount = true;
BECount = getCouldNotCompute();
} else if (!CouldNotComputeBECount) {
if (BECount == getCouldNotCompute())
BECount = NewBTI.Exact;
else
BECount = getUMinFromMismatchedTypes(BECount, NewBTI.Exact);
}
CouldComputeBECount = false;
else
ExitCounts.push_back(std::make_pair(ExitingBlocks[i], EL.Exact));
if (MaxBECount == getCouldNotCompute())
MaxBECount = NewBTI.Max;
else if (NewBTI.Max != getCouldNotCompute())
MaxBECount = getUMinFromMismatchedTypes(MaxBECount, NewBTI.Max);
MaxBECount = EL.Max;
else if (EL.Max != getCouldNotCompute())
MaxBECount = getUMinFromMismatchedTypes(MaxBECount, EL.Max);
}
return BackedgeTakenInfo(BECount, MaxBECount);
return BackedgeTakenInfo(ExitCounts, CouldComputeBECount, MaxBECount);
}
/// ComputeBackedgeTakenCountFromExit - Compute the number of times the backedge
/// of the specified loop will execute if it exits via the specified block.
ScalarEvolution::BackedgeTakenInfo
ScalarEvolution::ComputeBackedgeTakenCountFromExit(const Loop *L,
BasicBlock *ExitingBlock) {
/// ComputeExitLimit - Compute the number of times the backedge of the specified
/// loop will execute if it exits via the specified block.
ScalarEvolution::ExitLimit
ScalarEvolution::ComputeExitLimit(const Loop *L, BasicBlock *ExitingBlock) {
// Okay, we've chosen an exiting block. See what condition causes us to
// exit at this block.
@ -4081,95 +4162,91 @@ ScalarEvolution::ComputeBackedgeTakenCountFromExit(const Loop *L,
}
// Proceed to the next level to examine the exit condition expression.
return ComputeBackedgeTakenCountFromExitCond(L, ExitBr->getCondition(),
ExitBr->getSuccessor(0),
ExitBr->getSuccessor(1));
return ComputeExitLimitFromCond(L, ExitBr->getCondition(),
ExitBr->getSuccessor(0),
ExitBr->getSuccessor(1));
}
/// ComputeBackedgeTakenCountFromExitCond - Compute the number of times the
/// ComputeExitLimitFromCond - Compute the number of times the
/// backedge of the specified loop will execute if its exit condition
/// were a conditional branch of ExitCond, TBB, and FBB.
ScalarEvolution::BackedgeTakenInfo
ScalarEvolution::ComputeBackedgeTakenCountFromExitCond(const Loop *L,
Value *ExitCond,
BasicBlock *TBB,
BasicBlock *FBB) {
ScalarEvolution::ExitLimit
ScalarEvolution::ComputeExitLimitFromCond(const Loop *L,
Value *ExitCond,
BasicBlock *TBB,
BasicBlock *FBB) {
// Check if the controlling expression for this loop is an And or Or.
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(ExitCond)) {
if (BO->getOpcode() == Instruction::And) {
// Recurse on the operands of the and.
BackedgeTakenInfo BTI0 =
ComputeBackedgeTakenCountFromExitCond(L, BO->getOperand(0), TBB, FBB);
BackedgeTakenInfo BTI1 =
ComputeBackedgeTakenCountFromExitCond(L, BO->getOperand(1), TBB, FBB);
ExitLimit EL0 = ComputeExitLimitFromCond(L, BO->getOperand(0), TBB, FBB);
ExitLimit EL1 = ComputeExitLimitFromCond(L, BO->getOperand(1), TBB, FBB);
const SCEV *BECount = getCouldNotCompute();
const SCEV *MaxBECount = getCouldNotCompute();
if (L->contains(TBB)) {
// Both conditions must be true for the loop to continue executing.
// Choose the less conservative count.
if (BTI0.Exact == getCouldNotCompute() ||
BTI1.Exact == getCouldNotCompute())
if (EL0.Exact == getCouldNotCompute() ||
EL1.Exact == getCouldNotCompute())
BECount = getCouldNotCompute();
else
BECount = getUMinFromMismatchedTypes(BTI0.Exact, BTI1.Exact);
if (BTI0.Max == getCouldNotCompute())
MaxBECount = BTI1.Max;
else if (BTI1.Max == getCouldNotCompute())
MaxBECount = BTI0.Max;
BECount = getUMinFromMismatchedTypes(EL0.Exact, EL1.Exact);
if (EL0.Max == getCouldNotCompute())
MaxBECount = EL1.Max;
else if (EL1.Max == getCouldNotCompute())
MaxBECount = EL0.Max;
else
MaxBECount = getUMinFromMismatchedTypes(BTI0.Max, BTI1.Max);
MaxBECount = getUMinFromMismatchedTypes(EL0.Max, EL1.Max);
} else {
// Both conditions must be true at the same time for the loop to exit.
// For now, be conservative.
assert(L->contains(FBB) && "Loop block has no successor in loop!");
if (BTI0.Max == BTI1.Max)
MaxBECount = BTI0.Max;
if (BTI0.Exact == BTI1.Exact)
BECount = BTI0.Exact;
if (EL0.Max == EL1.Max)
MaxBECount = EL0.Max;
if (EL0.Exact == EL1.Exact)
BECount = EL0.Exact;
}
return BackedgeTakenInfo(BECount, MaxBECount);
return ExitLimit(BECount, MaxBECount);
}
if (BO->getOpcode() == Instruction::Or) {
// Recurse on the operands of the or.
BackedgeTakenInfo BTI0 =
ComputeBackedgeTakenCountFromExitCond(L, BO->getOperand(0), TBB, FBB);
BackedgeTakenInfo BTI1 =
ComputeBackedgeTakenCountFromExitCond(L, BO->getOperand(1), TBB, FBB);
ExitLimit EL0 = ComputeExitLimitFromCond(L, BO->getOperand(0), TBB, FBB);
ExitLimit EL1 = ComputeExitLimitFromCond(L, BO->getOperand(1), TBB, FBB);
const SCEV *BECount = getCouldNotCompute();
const SCEV *MaxBECount = getCouldNotCompute();
if (L->contains(FBB)) {
// Both conditions must be false for the loop to continue executing.
// Choose the less conservative count.
if (BTI0.Exact == getCouldNotCompute() ||
BTI1.Exact == getCouldNotCompute())
if (EL0.Exact == getCouldNotCompute() ||
EL1.Exact == getCouldNotCompute())
BECount = getCouldNotCompute();
else
BECount = getUMinFromMismatchedTypes(BTI0.Exact, BTI1.Exact);
if (BTI0.Max == getCouldNotCompute())
MaxBECount = BTI1.Max;
else if (BTI1.Max == getCouldNotCompute())
MaxBECount = BTI0.Max;
BECount = getUMinFromMismatchedTypes(EL0.Exact, EL1.Exact);
if (EL0.Max == getCouldNotCompute())
MaxBECount = EL1.Max;
else if (EL1.Max == getCouldNotCompute())
MaxBECount = EL0.Max;
else
MaxBECount = getUMinFromMismatchedTypes(BTI0.Max, BTI1.Max);
MaxBECount = getUMinFromMismatchedTypes(EL0.Max, EL1.Max);
} else {
// Both conditions must be false at the same time for the loop to exit.
// For now, be conservative.
assert(L->contains(TBB) && "Loop block has no successor in loop!");
if (BTI0.Max == BTI1.Max)
MaxBECount = BTI0.Max;
if (BTI0.Exact == BTI1.Exact)
BECount = BTI0.Exact;
if (EL0.Max == EL1.Max)
MaxBECount = EL0.Max;
if (EL0.Exact == EL1.Exact)
BECount = EL0.Exact;
}
return BackedgeTakenInfo(BECount, MaxBECount);
return ExitLimit(BECount, MaxBECount);
}
}
// With an icmp, it may be feasible to compute an exact backedge-taken count.
// Proceed to the next level to examine the icmp.
if (ICmpInst *ExitCondICmp = dyn_cast<ICmpInst>(ExitCond))
return ComputeBackedgeTakenCountFromExitCondICmp(L, ExitCondICmp, TBB, FBB);
return ComputeExitLimitFromICmp(L, ExitCondICmp, TBB, FBB);
// Check for a constant condition. These are normally stripped out by
// SimplifyCFG, but ScalarEvolution may be used by a pass which wishes to
@ -4185,17 +4262,17 @@ ScalarEvolution::ComputeBackedgeTakenCountFromExitCond(const Loop *L,
}
// If it's not an integer or pointer comparison then compute it the hard way.
return ComputeBackedgeTakenCountExhaustively(L, ExitCond, !L->contains(TBB));
return ComputeExitCountExhaustively(L, ExitCond, !L->contains(TBB));
}
/// ComputeBackedgeTakenCountFromExitCondICmp - Compute the number of times the
/// ComputeExitLimitFromICmp - Compute the number of times the
/// backedge of the specified loop will execute if its exit condition
/// were a conditional branch of the ICmpInst ExitCond, TBB, and FBB.
ScalarEvolution::BackedgeTakenInfo
ScalarEvolution::ComputeBackedgeTakenCountFromExitCondICmp(const Loop *L,
ICmpInst *ExitCond,
BasicBlock *TBB,
BasicBlock *FBB) {
ScalarEvolution::ExitLimit
ScalarEvolution::ComputeExitLimitFromICmp(const Loop *L,
ICmpInst *ExitCond,
BasicBlock *TBB,
BasicBlock *FBB) {
// If the condition was exit on true, convert the condition to exit on false
ICmpInst::Predicate Cond;
@ -4207,8 +4284,8 @@ ScalarEvolution::ComputeBackedgeTakenCountFromExitCondICmp(const Loop *L,
// Handle common loops like: for (X = "string"; *X; ++X)
if (LoadInst *LI = dyn_cast<LoadInst>(ExitCond->getOperand(0)))
if (Constant *RHS = dyn_cast<Constant>(ExitCond->getOperand(1))) {
BackedgeTakenInfo ItCnt =
ComputeLoadConstantCompareBackedgeTakenCount(LI, RHS, L, Cond);
ExitLimit ItCnt =
ComputeLoadConstantCompareExitLimit(LI, RHS, L, Cond);
if (ItCnt.hasAnyInfo())
return ItCnt;
}
@ -4247,36 +4324,36 @@ ScalarEvolution::ComputeBackedgeTakenCountFromExitCondICmp(const Loop *L,
switch (Cond) {
case ICmpInst::ICMP_NE: { // while (X != Y)
// Convert to: while (X-Y != 0)
BackedgeTakenInfo BTI = HowFarToZero(getMinusSCEV(LHS, RHS), L);
if (BTI.hasAnyInfo()) return BTI;
ExitLimit EL = HowFarToZero(getMinusSCEV(LHS, RHS), L);
if (EL.hasAnyInfo()) return EL;
break;
}
case ICmpInst::ICMP_EQ: { // while (X == Y)
// Convert to: while (X-Y == 0)
BackedgeTakenInfo BTI = HowFarToNonZero(getMinusSCEV(LHS, RHS), L);
if (BTI.hasAnyInfo()) return BTI;
ExitLimit EL = HowFarToNonZero(getMinusSCEV(LHS, RHS), L);
if (EL.hasAnyInfo()) return EL;
break;
}
case ICmpInst::ICMP_SLT: {
BackedgeTakenInfo BTI = HowManyLessThans(LHS, RHS, L, true);
if (BTI.hasAnyInfo()) return BTI;
ExitLimit EL = HowManyLessThans(LHS, RHS, L, true);
if (EL.hasAnyInfo()) return EL;
break;
}
case ICmpInst::ICMP_SGT: {
BackedgeTakenInfo BTI = HowManyLessThans(getNotSCEV(LHS),
ExitLimit EL = HowManyLessThans(getNotSCEV(LHS),
getNotSCEV(RHS), L, true);
if (BTI.hasAnyInfo()) return BTI;
if (EL.hasAnyInfo()) return EL;
break;
}
case ICmpInst::ICMP_ULT: {
BackedgeTakenInfo BTI = HowManyLessThans(LHS, RHS, L, false);
if (BTI.hasAnyInfo()) return BTI;
ExitLimit EL = HowManyLessThans(LHS, RHS, L, false);
if (EL.hasAnyInfo()) return EL;
break;
}
case ICmpInst::ICMP_UGT: {
BackedgeTakenInfo BTI = HowManyLessThans(getNotSCEV(LHS),
ExitLimit EL = HowManyLessThans(getNotSCEV(LHS),
getNotSCEV(RHS), L, false);
if (BTI.hasAnyInfo()) return BTI;
if (EL.hasAnyInfo()) return EL;
break;
}
default:
@ -4290,8 +4367,7 @@ ScalarEvolution::ComputeBackedgeTakenCountFromExitCondICmp(const Loop *L,
#endif
break;
}
return
ComputeBackedgeTakenCountExhaustively(L, ExitCond, !L->contains(TBB));
return ComputeExitCountExhaustively(L, ExitCond, !L->contains(TBB));
}
static ConstantInt *
@ -4338,15 +4414,16 @@ GetAddressedElementFromGlobal(GlobalVariable *GV,
return Init;
}
/// ComputeLoadConstantCompareBackedgeTakenCount - Given an exit condition of
/// ComputeLoadConstantCompareExitLimit - Given an exit condition of
/// 'icmp op load X, cst', try to see if we can compute the backedge
/// execution count.
ScalarEvolution::BackedgeTakenInfo
ScalarEvolution::ComputeLoadConstantCompareBackedgeTakenCount(
LoadInst *LI,
Constant *RHS,
const Loop *L,
ICmpInst::Predicate predicate) {
ScalarEvolution::ExitLimit
ScalarEvolution::ComputeLoadConstantCompareExitLimit(
LoadInst *LI,
Constant *RHS,
const Loop *L,
ICmpInst::Predicate predicate) {
if (LI->isVolatile()) return getCouldNotCompute();
// Check to see if the loaded pointer is a getelementptr of a global.
@ -4547,15 +4624,14 @@ ScalarEvolution::getConstantEvolutionLoopExitValue(PHINode *PN,
}
}
/// ComputeBackedgeTakenCountExhaustively - If the loop is known to execute a
/// ComputeExitCountExhaustively - If the loop is known to execute a
/// constant number of times (the condition evolves only from constants),
/// try to evaluate a few iterations of the loop until we get the exit
/// condition gets a value of ExitWhen (true or false). If we cannot
/// evaluate the trip count of the loop, return getCouldNotCompute().
const SCEV *
ScalarEvolution::ComputeBackedgeTakenCountExhaustively(const Loop *L,
Value *Cond,
bool ExitWhen) {
const SCEV * ScalarEvolution::ComputeExitCountExhaustively(const Loop *L,
Value *Cond,
bool ExitWhen) {
PHINode *PN = getConstantEvolvingPHI(Cond, L);
if (PN == 0) return getCouldNotCompute();
@ -4949,7 +5025,7 @@ SolveQuadraticEquation(const SCEVAddRecExpr *AddRec, ScalarEvolution &SE) {
/// now expressed as a single expression, V = x-y. So the exit test is
/// effectively V != 0. We know and take advantage of the fact that this
/// expression only being used in a comparison by zero context.
ScalarEvolution::BackedgeTakenInfo
ScalarEvolution::ExitLimit
ScalarEvolution::HowFarToZero(const SCEV *V, const Loop *L) {
// If the value is a constant
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(V)) {
@ -5061,7 +5137,7 @@ ScalarEvolution::HowFarToZero(const SCEV *V, const Loop *L) {
/// HowFarToNonZero - Return the number of times a backedge checking the
/// specified value for nonzero will execute. If not computable, return
/// CouldNotCompute
ScalarEvolution::BackedgeTakenInfo
ScalarEvolution::ExitLimit
ScalarEvolution::HowFarToNonZero(const SCEV *V, const Loop *L) {
// Loops that look like: while (X == 0) are very strange indeed. We don't
// handle them yet except for the trivial case. This could be expanded in the
@ -5774,7 +5850,7 @@ const SCEV *ScalarEvolution::getBECount(const SCEV *Start,
/// HowManyLessThans - Return the number of times a backedge containing the
/// specified less-than comparison will execute. If not computable, return
/// CouldNotCompute.
ScalarEvolution::BackedgeTakenInfo
ScalarEvolution::ExitLimit
ScalarEvolution::HowManyLessThans(const SCEV *LHS, const SCEV *RHS,
const Loop *L, bool isSigned) {
// Only handle: "ADDREC < LoopInvariant".
@ -5881,7 +5957,7 @@ ScalarEvolution::HowManyLessThans(const SCEV *LHS, const SCEV *RHS,
if (isa<SCEVCouldNotCompute>(MaxBECount))
MaxBECount = BECount;
return BackedgeTakenInfo(BECount, MaxBECount);
return ExitLimit(BECount, MaxBECount);
}
return getCouldNotCompute();
@ -6089,6 +6165,15 @@ void ScalarEvolution::releaseMemory() {
FirstUnknown = 0;
ValueExprMap.clear();
// Free any extra memory created for ExitNotTakenInfo in the unlikely event
// that a loop had multiple computable exits.
for (DenseMap<const Loop*, BackedgeTakenInfo>::iterator I =
BackedgeTakenCounts.begin(), E = BackedgeTakenCounts.end();
I != E; ++I) {
I->second.clear();
}
BackedgeTakenCounts.clear();
ConstantEvolutionLoopExitValue.clear();
ValuesAtScopes.clear();