6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2025-06-25 16:24:23 +00:00
Code Issues Projects Releases Wiki Activity

Rename ScalarEvolution's getIterationCount to getBackedgeTakenCount,

Browse Source 
to more accurately describe what it does. Expand its doxygen comment
to describe what the backedge-taken count is and how it differs
from the actual iteration count of the loop. Adjust names and
comments in associated code accordingly.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@65382 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2009-02-24 18:55:53 +00:00
parent 57f0db833d
commit 46bdfb0e6b
21 changed files with 177 additions and 145 deletions
Download Patch File Download Diff File Expand all files Collapse all files

173
lib/Analysis/ScalarEvolution.cpp
View File

@ -1419,9 +1419,9 @@ namespace {
///
std::map<Value*, SCEVHandle> Scalars;
/// IterationCounts - Cache the iteration count of the loops for this
/// function as they are computed.
std::map<const Loop*, SCEVHandle> IterationCounts;
/// BackedgeTakenCounts - Cache the backedge-taken count of the loops for
/// this function as they are computed.
std::map<const Loop*, SCEVHandle> BackedgeTakenCounts;
/// ConstantEvolutionLoopExitValue - This map contains entries for all of
/// the PHI instructions that we attempt to compute constant evolutions for.
@ -1464,19 +1464,28 @@ namespace {
bool isLoopGuardedByCond(const Loop *L, ICmpInst::Predicate Pred,
SCEV *LHS, SCEV *RHS);
/// hasLoopInvariantIterationCount - Return true if the specified loop has
/// an analyzable loop-invariant iteration count.
bool hasLoopInvariantIterationCount(const Loop *L);
/// hasLoopInvariantBackedgeTakenCount - Return true if the specified loop
/// has an analyzable loop-invariant backedge-taken count.
bool hasLoopInvariantBackedgeTakenCount(const Loop *L);
/// forgetLoopIterationCount - This method should be called by the
/// forgetLoopBackedgeTakenCount - This method should be called by the
/// client when it has changed a loop in a way that may effect
/// ScalarEvolution's ability to compute a trip count.
void forgetLoopIterationCount(const Loop *L);
/// ScalarEvolution's ability to compute a trip count, or if the loop
/// is deleted.
void forgetLoopBackedgeTakenCount(const Loop *L);
/// getIterationCount - If the specified loop has a predictable iteration
/// count, return it. Note that it is not valid to call this method on a
/// loop without a loop-invariant iteration count.
SCEVHandle getIterationCount(const Loop *L);
/// 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
/// will be branched to from within the loop. This is one less than the
/// trip count of the loop, since it doesn't count the first iteration,
/// when the header is branched to from outside the loop.
///
/// Note that it is not valid to call this method on a loop without a
/// loop-invariant backedge-taken count (see
/// hasLoopInvariantBackedgeTakenCount).
///
SCEVHandle getBackedgeTakenCount(const Loop *L);
/// deleteValueFromRecords - This method should be called by the
/// client before it removes a value from the program, to make sure
@ -1500,24 +1509,25 @@ namespace {
const SCEVHandle &SymName,
const SCEVHandle &NewVal);
/// ComputeIterationCount - Compute the number of times the specified loop
/// will iterate.
SCEVHandle ComputeIterationCount(const Loop *L);
/// ComputeBackedgeTakenCount - Compute the number of times the specified
/// loop will iterate.
SCEVHandle ComputeBackedgeTakenCount(const Loop *L);
/// ComputeLoadConstantCompareIterationCount - Given an exit condition of
/// 'icmp op load X, cst', try to see if we can compute the trip count.
SCEVHandle ComputeLoadConstantCompareIterationCount(LoadInst *LI,
Constant *RHS,
const Loop *L,
ICmpInst::Predicate p);
/// ComputeLoadConstantCompareBackedgeTakenCount - Given an exit condition
/// of 'icmp op load X, cst', try to see if we can compute the trip count.
SCEVHandle
ComputeLoadConstantCompareBackedgeTakenCount(LoadInst *LI,
Constant *RHS,
const Loop *L,
ICmpInst::Predicate p);
/// ComputeIterationCountExhaustively - If the trip is known to execute a
/// constant number of times (the condition evolves only from constants),
/// ComputeBackedgeTakenCountExhaustively - If the trip 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 UnknownValue.
SCEVHandle ComputeIterationCountExhaustively(const Loop *L, Value *Cond,
bool ExitWhen);
SCEVHandle ComputeBackedgeTakenCountExhaustively(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
@ -1545,7 +1555,7 @@ namespace {
/// in the header of its containing loop, we know the loop executes a
/// constant number of times, and the PHI node is just a recurrence
/// involving constants, fold it.
Constant *getConstantEvolutionLoopExitValue(PHINode *PN, const APInt& Its,
Constant *getConstantEvolutionLoopExitValue(PHINode *PN, const APInt& BEs,
const Loop *L);
};
}
@ -1931,14 +1941,22 @@ SCEVHandle ScalarEvolutionsImpl::createSCEV(Value *V) {
// Iteration Count Computation Code
//
/// getIterationCount - If the specified loop has a predictable iteration
/// count, return it. Note that it is not valid to call this method on a
/// loop without a loop-invariant iteration count.
SCEVHandle ScalarEvolutionsImpl::getIterationCount(const Loop *L) {
std::map<const Loop*, SCEVHandle>::iterator I = IterationCounts.find(L);
if (I == IterationCounts.end()) {
SCEVHandle ItCount = ComputeIterationCount(L);
I = IterationCounts.insert(std::make_pair(L, ItCount)).first;
/// 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
/// will be branched to from within the loop. This is one less than the
/// trip count of the loop, since it doesn't count the first iteration,
/// when the header is branched to from outside the loop.
///
/// Note that it is not valid to call this method on a loop without a
/// loop-invariant backedge-taken count (see
/// hasLoopInvariantBackedgeTakenCount).
///
SCEVHandle ScalarEvolutionsImpl::getBackedgeTakenCount(const Loop *L) {
std::map<const Loop*, SCEVHandle>::iterator I = BackedgeTakenCounts.find(L);
if (I == BackedgeTakenCounts.end()) {
SCEVHandle ItCount = ComputeBackedgeTakenCount(L);
I = BackedgeTakenCounts.insert(std::make_pair(L, ItCount)).first;
if (ItCount != UnknownValue) {
assert(ItCount->isLoopInvariant(L) &&
"Computed trip count isn't loop invariant for loop!");
@ -1951,16 +1969,17 @@ SCEVHandle ScalarEvolutionsImpl::getIterationCount(const Loop *L) {
return I->second;
}
/// forgetLoopIterationCount - This method should be called by the
/// forgetLoopBackedgeTakenCount - This method should be called by the
/// client when it has changed a loop in a way that may effect
/// ScalarEvolution's ability to compute a trip count.
void ScalarEvolutionsImpl::forgetLoopIterationCount(const Loop *L) {
IterationCounts.erase(L);
/// ScalarEvolution's ability to compute a trip count, or if the loop
/// is deleted.
void ScalarEvolutionsImpl::forgetLoopBackedgeTakenCount(const Loop *L) {
BackedgeTakenCounts.erase(L);
}
/// ComputeIterationCount - Compute the number of times the specified loop
/// will iterate.
SCEVHandle ScalarEvolutionsImpl::ComputeIterationCount(const Loop *L) {
/// ComputeBackedgeTakenCount - Compute the number of times the backedge
/// of the specified loop will execute.
SCEVHandle ScalarEvolutionsImpl::ComputeBackedgeTakenCount(const Loop *L) {
// If the loop has a non-one exit block count, we can't analyze it.
SmallVector<BasicBlock*, 8> ExitBlocks;
L->getExitBlocks(ExitBlocks);
@ -2010,7 +2029,7 @@ SCEVHandle ScalarEvolutionsImpl::ComputeIterationCount(const Loop *L) {
// Note that ICmpInst deals with pointer comparisons too so we must check
// the type of the operand.
if (ExitCond == 0 || isa<PointerType>(ExitCond->getOperand(0)->getType()))
return ComputeIterationCountExhaustively(L, ExitBr->getCondition(),
return ComputeBackedgeTakenCountExhaustively(L, ExitBr->getCondition(),
ExitBr->getSuccessor(0) == ExitBlock);
// If the condition was exit on true, convert the condition to exit on false
@ -2024,7 +2043,7 @@ SCEVHandle ScalarEvolutionsImpl::ComputeIterationCount(const Loop *L) {
if (LoadInst *LI = dyn_cast<LoadInst>(ExitCond->getOperand(0)))
if (Constant *RHS = dyn_cast<Constant>(ExitCond->getOperand(1))) {
SCEVHandle ItCnt =
ComputeLoadConstantCompareIterationCount(LI, RHS, L, Cond);
ComputeLoadConstantCompareBackedgeTakenCount(LI, RHS, L, Cond);
if (!isa<SCEVCouldNotCompute>(ItCnt)) return ItCnt;
}
@ -2107,7 +2126,7 @@ SCEVHandle ScalarEvolutionsImpl::ComputeIterationCount(const Loop *L) {
}
default:
#if 0
cerr << "ComputeIterationCount ";
cerr << "ComputeBackedgeTakenCount ";
if (ExitCond->getOperand(0)->getType()->isUnsigned())
cerr << "[unsigned] ";
cerr << *LHS << " "
@ -2116,8 +2135,9 @@ SCEVHandle ScalarEvolutionsImpl::ComputeIterationCount(const Loop *L) {
#endif
break;
}
return ComputeIterationCountExhaustively(L, ExitCond,
ExitBr->getSuccessor(0) == ExitBlock);
return
ComputeBackedgeTakenCountExhaustively(L, ExitCond,
ExitBr->getSuccessor(0) == ExitBlock);
}
static ConstantInt *
@ -2164,12 +2184,13 @@ GetAddressedElementFromGlobal(GlobalVariable *GV,
return Init;
}
/// ComputeLoadConstantCompareIterationCount - Given an exit condition of
/// 'icmp op load X, cst', try to see if we can compute the trip count.
/// ComputeLoadConstantCompareBackedgeTakenCount - Given an exit condition of
/// 'icmp op load X, cst', try to see if we can compute the backedge
/// execution count.
SCEVHandle ScalarEvolutionsImpl::
ComputeLoadConstantCompareIterationCount(LoadInst *LI, Constant *RHS,
const Loop *L,
ICmpInst::Predicate predicate) {
ComputeLoadConstantCompareBackedgeTakenCount(LoadInst *LI, Constant *RHS,
const Loop *L,
ICmpInst::Predicate predicate) {
if (LI->isVolatile()) return UnknownValue;
// Check to see if the loaded pointer is a getelementptr of a global.
@ -2326,13 +2347,13 @@ static Constant *EvaluateExpression(Value *V, Constant *PHIVal) {
/// constant number of times, and the PHI node is just a recurrence
/// involving constants, fold it.
Constant *ScalarEvolutionsImpl::
getConstantEvolutionLoopExitValue(PHINode *PN, const APInt& Its, const Loop *L){
getConstantEvolutionLoopExitValue(PHINode *PN, const APInt& BEs, const Loop *L){
std::map<PHINode*, Constant*>::iterator I =
ConstantEvolutionLoopExitValue.find(PN);
if (I != ConstantEvolutionLoopExitValue.end())
return I->second;
if (Its.ugt(APInt(Its.getBitWidth(),MaxBruteForceIterations)))
if (BEs.ugt(APInt(BEs.getBitWidth(),MaxBruteForceIterations)))
return ConstantEvolutionLoopExitValue[PN] = 0; // Not going to evaluate it.
Constant *&RetVal = ConstantEvolutionLoopExitValue[PN];
@ -2352,10 +2373,10 @@ getConstantEvolutionLoopExitValue(PHINode *PN, const APInt& Its, const Loop *L){
return RetVal = 0; // Not derived from same PHI.
// Execute the loop symbolically to determine the exit value.
if (Its.getActiveBits() >= 32)
if (BEs.getActiveBits() >= 32)
return RetVal = 0; // More than 2^32-1 iterations?? Not doing it!
unsigned NumIterations = Its.getZExtValue(); // must be in range
unsigned NumIterations = BEs.getZExtValue(); // must be in range
unsigned IterationNum = 0;
for (Constant *PHIVal = StartCST; ; ++IterationNum) {
if (IterationNum == NumIterations)
@ -2371,13 +2392,13 @@ getConstantEvolutionLoopExitValue(PHINode *PN, const APInt& Its, const Loop *L){
}
}
/// ComputeIterationCountExhaustively - If the trip is known to execute a
/// ComputeBackedgeTakenCountExhaustively - If the trip 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 UnknownValue.
SCEVHandle ScalarEvolutionsImpl::
ComputeIterationCountExhaustively(const Loop *L, Value *Cond, bool ExitWhen) {
ComputeBackedgeTakenCountExhaustively(const Loop *L, Value *Cond, bool ExitWhen) {
PHINode *PN = getConstantEvolvingPHI(Cond, L);
if (PN == 0) return UnknownValue;
@ -2440,15 +2461,17 @@ SCEVHandle ScalarEvolutionsImpl::getSCEVAtScope(SCEV *V, const Loop *L) {
if (PHINode *PN = dyn_cast<PHINode>(I))
if (PN->getParent() == LI->getHeader()) {
// Okay, there is no closed form solution for the PHI node. Check
// to see if the loop that contains it has a known iteration count.
// If so, we may be able to force computation of the exit value.
SCEVHandle IterationCount = getIterationCount(LI);
if (SCEVConstant *ICC = dyn_cast<SCEVConstant>(IterationCount)) {
// to see if the loop that contains it has a known backedge-taken
// count. If so, we may be able to force computation of the exit
// value.
SCEVHandle BackedgeTakenCount = getBackedgeTakenCount(LI);
if (SCEVConstant *BTCC =
dyn_cast<SCEVConstant>(BackedgeTakenCount)) {
// Okay, we know how many times the containing loop executes. If
// this is a constant evolving PHI node, get the final value at
// the specified iteration number.
Constant *RV = getConstantEvolutionLoopExitValue(PN,
ICC->getValue()->getValue(),
BTCC->getValue()->getValue(),
LI);
if (RV) return SE.getUnknown(RV);
}
@ -2552,11 +2575,11 @@ SCEVHandle ScalarEvolutionsImpl::getSCEVAtScope(SCEV *V, const Loop *L) {
if (!L || !AddRec->getLoop()->contains(L->getHeader())) {
// To evaluate this recurrence, we need to know how many times the AddRec
// loop iterates. Compute this now.
SCEVHandle IterationCount = getIterationCount(AddRec->getLoop());
if (IterationCount == UnknownValue) return UnknownValue;
SCEVHandle BackedgeTakenCount = getBackedgeTakenCount(AddRec->getLoop());
if (BackedgeTakenCount == UnknownValue) return UnknownValue;
// Then, evaluate the AddRec.
return AddRec->evaluateAtIteration(IterationCount, SE);
return AddRec->evaluateAtIteration(BackedgeTakenCount, SE);
}
return UnknownValue;
}
@ -3110,16 +3133,16 @@ bool ScalarEvolution::isLoopGuardedByCond(const Loop *L,
LHS, RHS);
}
SCEVHandle ScalarEvolution::getIterationCount(const Loop *L) const {
return ((ScalarEvolutionsImpl*)Impl)->getIterationCount(L);
SCEVHandle ScalarEvolution::getBackedgeTakenCount(const Loop *L) const {
return ((ScalarEvolutionsImpl*)Impl)->getBackedgeTakenCount(L);
}
bool ScalarEvolution::hasLoopInvariantIterationCount(const Loop *L) const {
return !isa<SCEVCouldNotCompute>(getIterationCount(L));
bool ScalarEvolution::hasLoopInvariantBackedgeTakenCount(const Loop *L) const {
return !isa<SCEVCouldNotCompute>(getBackedgeTakenCount(L));
}
void ScalarEvolution::forgetLoopIterationCount(const Loop *L) {
return ((ScalarEvolutionsImpl*)Impl)->forgetLoopIterationCount(L);
void ScalarEvolution::forgetLoopBackedgeTakenCount(const Loop *L) {
return ((ScalarEvolutionsImpl*)Impl)->forgetLoopBackedgeTakenCount(L);
}
SCEVHandle ScalarEvolution::getSCEVAtScope(Value *V, const Loop *L) const {
@ -3143,10 +3166,10 @@ static void PrintLoopInfo(std::ostream &OS, const ScalarEvolution *SE,
if (ExitBlocks.size() != 1)
OS << "<multiple exits> ";
if (SE->hasLoopInvariantIterationCount(L)) {
OS << *SE->getIterationCount(L) << " iterations! ";
if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
OS << "backedge-taken count is " << *SE->getBackedgeTakenCount(L);
} else {
OS << "Unpredictable iteration count. ";
OS << "Unpredictable backedge-taken count. ";
}
OS << "\n";