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llvm-project/llvm/lib/Analysis/LoopCacheAnalysis.cpp

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//===- LoopCacheAnalysis.cpp - Loop Cache Analysis -------------------------==//
//
// The LLVM Compiler Infrastructure
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file defines the implementation for the loop cache analysis.
/// The implementation is largely based on the following paper:
///
/// Compiler Optimizations for Improving Data Locality
/// By: Steve Carr, Katherine S. McKinley, Chau-Wen Tseng
/// http://www.cs.utexas.edu/users/mckinley/papers/asplos-1994.pdf
///
/// The general approach taken to estimate the number of cache lines used by the
/// memory references in an inner loop is:
/// 1. Partition memory references that exhibit temporal or spacial reuse
/// into reference groups.
/// 2. For each loop L in the a loop nest LN:
/// a. Compute the cost of the reference group
/// b. Compute the loop cost by summing up the reference groups costs
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/LoopCacheAnalysis.h"
#include "llvm/ADT/BreadthFirstIterator.h"
#include "llvm/ADT/Sequence.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/Delinearization.h"
#include "llvm/Analysis/DependenceAnalysis.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
using namespace llvm;
#define DEBUG_TYPE "loop-cache-cost"
static cl::opt<unsigned> DefaultTripCount(
"default-trip-count", cl::init(100), cl::Hidden,
cl::desc("Use this to specify the default trip count of a loop"));
// In this analysis two array references are considered to exhibit temporal
// reuse if they access either the same memory location, or a memory location
// with distance smaller than a configurable threshold.
static cl::opt<unsigned> TemporalReuseThreshold(
"temporal-reuse-threshold", cl::init(2), cl::Hidden,
cl::desc("Use this to specify the max. distance between array elements "
"accessed in a loop so that the elements are classified to have "
"temporal reuse"));
/// Retrieve the innermost loop in the given loop nest \p Loops. It returns a
/// nullptr if any loops in the loop vector supplied has more than one sibling.
/// The loop vector is expected to contain loops collected in breadth-first
/// order.
static Loop *getInnerMostLoop(const LoopVectorTy &Loops) {
assert(!Loops.empty() && "Expecting a non-empy loop vector");
Loop *LastLoop = Loops.back();
Loop *ParentLoop = LastLoop->getParentLoop();
if (ParentLoop == nullptr) {
assert(Loops.size() == 1 && "Expecting a single loop");
return LastLoop;
}
return (llvm::is_sorted(Loops,
[](const Loop *L1, const Loop *L2) {
return L1->getLoopDepth() < L2->getLoopDepth();
}))
? LastLoop
: nullptr;
}
static bool isOneDimensionalArray(const SCEV &AccessFn, const SCEV &ElemSize,
const Loop &L, ScalarEvolution &SE) {
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(&AccessFn);
if (!AR || !AR->isAffine())
return false;
assert(AR->getLoop() && "AR should have a loop");
// Check that start and increment are not add recurrences.
const SCEV *Start = AR->getStart();
const SCEV *Step = AR->getStepRecurrence(SE);
if (isa<SCEVAddRecExpr>(Start) || isa<SCEVAddRecExpr>(Step))
return false;
// Check that start and increment are both invariant in the loop.
if (!SE.isLoopInvariant(Start, &L) || !SE.isLoopInvariant(Step, &L))
return false;
const SCEV *StepRec = AR->getStepRecurrence(SE);
if (StepRec && SE.isKnownNegative(StepRec))
StepRec = SE.getNegativeSCEV(StepRec);
return StepRec == &ElemSize;
}
/// Compute the trip count for the given loop \p L or assume a default value if
/// it is not a compile time constant. Return the SCEV expression for the trip
/// count.
static const SCEV *computeTripCount(const Loop &L, const SCEV &ElemSize,
ScalarEvolution &SE) {
const SCEV *BackedgeTakenCount = SE.getBackedgeTakenCount(&L);
const SCEV *TripCount = (!isa<SCEVCouldNotCompute>(BackedgeTakenCount) &&
isa<SCEVConstant>(BackedgeTakenCount))
? SE.getTripCountFromExitCount(BackedgeTakenCount)
: nullptr;
if (!TripCount) {
LLVM_DEBUG(dbgs() << "Trip count of loop " << L.getName()
<< " could not be computed, using DefaultTripCount\n");
TripCount = SE.getConstant(ElemSize.getType(), DefaultTripCount);
}
return TripCount;
}
//===----------------------------------------------------------------------===//
// IndexedReference implementation
//
raw_ostream &llvm::operator<<(raw_ostream &OS, const IndexedReference &R) {
if (!R.IsValid) {
OS << R.StoreOrLoadInst;
OS << ", IsValid=false.";
return OS;
}
OS << *R.BasePointer;
for (const SCEV *Subscript : R.Subscripts)
OS << "[" << *Subscript << "]";
OS << ", Sizes: ";
for (const SCEV *Size : R.Sizes)
OS << "[" << *Size << "]";
return OS;
}
IndexedReference::IndexedReference(Instruction &StoreOrLoadInst,
const LoopInfo &LI, ScalarEvolution &SE)
: StoreOrLoadInst(StoreOrLoadInst), SE(SE) {
assert((isa<StoreInst>(StoreOrLoadInst) || isa<LoadInst>(StoreOrLoadInst)) &&
"Expecting a load or store instruction");
IsValid = delinearize(LI);
if (IsValid)
LLVM_DEBUG(dbgs().indent(2) << "Succesfully delinearized: " << *this
<< "\n");
}
Optional<bool> IndexedReference::hasSpacialReuse(const IndexedReference &Other,
unsigned CLS,
AAResults &AA) const {
assert(IsValid && "Expecting a valid reference");
if (BasePointer != Other.getBasePointer() && !isAliased(Other, AA)) {
LLVM_DEBUG(dbgs().indent(2)
<< "No spacial reuse: different base pointers\n");
return false;
}
unsigned NumSubscripts = getNumSubscripts();
if (NumSubscripts != Other.getNumSubscripts()) {
LLVM_DEBUG(dbgs().indent(2)
<< "No spacial reuse: different number of subscripts\n");
return false;
}
// all subscripts must be equal, except the leftmost one (the last one).
for (auto SubNum : seq<unsigned>(0, NumSubscripts - 1)) {
if (getSubscript(SubNum) != Other.getSubscript(SubNum)) {
LLVM_DEBUG(dbgs().indent(2) << "No spacial reuse, different subscripts: "
<< "\n\t" << *getSubscript(SubNum) << "\n\t"
<< *Other.getSubscript(SubNum) << "\n");
return false;
}
}
// the difference between the last subscripts must be less than the cache line
// size.
const SCEV *LastSubscript = getLastSubscript();
const SCEV *OtherLastSubscript = Other.getLastSubscript();
const SCEVConstant *Diff = dyn_cast<SCEVConstant>(
SE.getMinusSCEV(LastSubscript, OtherLastSubscript));
if (Diff == nullptr) {
LLVM_DEBUG(dbgs().indent(2)
<< "No spacial reuse, difference between subscript:\n\t"
<< *LastSubscript << "\n\t" << OtherLastSubscript
<< "\nis not constant.\n");
return None;
}
bool InSameCacheLine = (Diff->getValue()->getSExtValue() < CLS);
LLVM_DEBUG({
if (InSameCacheLine)
dbgs().indent(2) << "Found spacial reuse.\n";
else
dbgs().indent(2) << "No spacial reuse.\n";
});
return InSameCacheLine;
}
Optional<bool> IndexedReference::hasTemporalReuse(const IndexedReference &Other,
unsigned MaxDistance,
const Loop &L,
DependenceInfo &DI,
AAResults &AA) const {
assert(IsValid && "Expecting a valid reference");
if (BasePointer != Other.getBasePointer() && !isAliased(Other, AA)) {
LLVM_DEBUG(dbgs().indent(2)
<< "No temporal reuse: different base pointer\n");
return false;
}
std::unique_ptr<Dependence> D =
DI.depends(&StoreOrLoadInst, &Other.StoreOrLoadInst, true);
if (D == nullptr) {
LLVM_DEBUG(dbgs().indent(2) << "No temporal reuse: no dependence\n");
return false;
}
if (D->isLoopIndependent()) {
LLVM_DEBUG(dbgs().indent(2) << "Found temporal reuse\n");
return true;
}
// Check the dependence distance at every loop level. There is temporal reuse
// if the distance at the given loop's depth is small (|d| <= MaxDistance) and
// it is zero at every other loop level.
int LoopDepth = L.getLoopDepth();
int Levels = D->getLevels();
for (int Level = 1; Level <= Levels; ++Level) {
const SCEV *Distance = D->getDistance(Level);
const SCEVConstant *SCEVConst = dyn_cast_or_null<SCEVConstant>(Distance);
if (SCEVConst == nullptr) {
LLVM_DEBUG(dbgs().indent(2) << "No temporal reuse: distance unknown\n");
return None;
}
const ConstantInt &CI = *SCEVConst->getValue();
if (Level != LoopDepth && !CI.isZero()) {
LLVM_DEBUG(dbgs().indent(2)
<< "No temporal reuse: distance is not zero at depth=" << Level
<< "\n");
return false;
} else if (Level == LoopDepth && CI.getSExtValue() > MaxDistance) {
LLVM_DEBUG(
dbgs().indent(2)
<< "No temporal reuse: distance is greater than MaxDistance at depth="
<< Level << "\n");
return false;
}
}
LLVM_DEBUG(dbgs().indent(2) << "Found temporal reuse\n");
return true;
}
CacheCostTy IndexedReference::computeRefCost(const Loop &L,
unsigned CLS) const {
assert(IsValid && "Expecting a valid reference");
LLVM_DEBUG({
dbgs().indent(2) << "Computing cache cost for:\n";
dbgs().indent(4) << *this << "\n";
});
// If the indexed reference is loop invariant the cost is one.
if (isLoopInvariant(L)) {
LLVM_DEBUG(dbgs().indent(4) << "Reference is loop invariant: RefCost=1\n");
return 1;
}
const SCEV *TripCount = computeTripCount(L, *Sizes.back(), SE);
assert(TripCount && "Expecting valid TripCount");
LLVM_DEBUG(dbgs() << "TripCount=" << *TripCount << "\n");
const SCEV *RefCost = nullptr;
const SCEV *Stride = nullptr;
if (isConsecutive(L, Stride, CLS)) {
// If the indexed reference is 'consecutive' the cost is
// (TripCount*Stride)/CLS.
assert(Stride != nullptr &&
"Stride should not be null for consecutive access!");
Type *WiderType = SE.getWiderType(Stride->getType(), TripCount->getType());
const SCEV *CacheLineSize = SE.getConstant(WiderType, CLS);
Stride = SE.getNoopOrAnyExtend(Stride, WiderType);
TripCount = SE.getNoopOrAnyExtend(TripCount, WiderType);
const SCEV *Numerator = SE.getMulExpr(Stride, TripCount);
RefCost = SE.getUDivExpr(Numerator, CacheLineSize);
LLVM_DEBUG(dbgs().indent(4)
<< "Access is consecutive: RefCost=(TripCount*Stride)/CLS="
<< *RefCost << "\n");
} else {
// If the indexed reference is not 'consecutive' the cost is proportional to
// the trip count and the depth of the dimension which the subject loop
// subscript is accessing. We try to estimate this by multiplying the cost
// by the trip counts of loops corresponding to the inner dimensions. For
// example, given the indexed reference 'A[i][j][k]', and assuming the
// i-loop is in the innermost position, the cost would be equal to the
// iterations of the i-loop multiplied by iterations of the j-loop.
RefCost = TripCount;
int Index = getSubscriptIndex(L);
assert(Index >= 0 && "Cound not locate a valid Index");
for (unsigned I = Index + 1; I < getNumSubscripts() - 1; ++I) {
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(getSubscript(I));
assert(AR && AR->getLoop() && "Expecting valid loop");
const SCEV *TripCount =
computeTripCount(*AR->getLoop(), *Sizes.back(), SE);
Type *WiderType = SE.getWiderType(RefCost->getType(), TripCount->getType());
RefCost = SE.getMulExpr(SE.getNoopOrAnyExtend(RefCost, WiderType),
SE.getNoopOrAnyExtend(TripCount, WiderType));
}
LLVM_DEBUG(dbgs().indent(4)
<< "Access is not consecutive: RefCost=" << *RefCost << "\n");
}
assert(RefCost && "Expecting a valid RefCost");
// Attempt to fold RefCost into a constant.
if (auto ConstantCost = dyn_cast<SCEVConstant>(RefCost))
return ConstantCost->getValue()->getSExtValue();
LLVM_DEBUG(dbgs().indent(4)
<< "RefCost is not a constant! Setting to RefCost=InvalidCost "
"(invalid value).\n");
return CacheCost::InvalidCost;
}
bool IndexedReference::tryDelinearizeFixedSize(
const SCEV *AccessFn, SmallVectorImpl<const SCEV *> &Subscripts) {
SmallVector<int, 4> ArraySizes;
if (!tryDelinearizeFixedSizeImpl(&SE, &StoreOrLoadInst, AccessFn, Subscripts,
ArraySizes))
return false;
// Populate Sizes with scev expressions to be used in calculations later.
for (auto Idx : seq<unsigned>(1, Subscripts.size()))
Sizes.push_back(
SE.getConstant(Subscripts[Idx]->getType(), ArraySizes[Idx - 1]));
LLVM_DEBUG({
dbgs() << "Delinearized subscripts of fixed-size array\n"
<< "GEP:" << *getLoadStorePointerOperand(&StoreOrLoadInst)
<< "\n";
});
return true;
}
bool IndexedReference::delinearize(const LoopInfo &LI) {
assert(Subscripts.empty() && "Subscripts should be empty");
assert(Sizes.empty() && "Sizes should be empty");
assert(!IsValid && "Should be called once from the constructor");
LLVM_DEBUG(dbgs() << "Delinearizing: " << StoreOrLoadInst << "\n");
const SCEV *ElemSize = SE.getElementSize(&StoreOrLoadInst);
const BasicBlock *BB = StoreOrLoadInst.getParent();
if (Loop *L = LI.getLoopFor(BB)) {
const SCEV *AccessFn =
SE.getSCEVAtScope(getPointerOperand(&StoreOrLoadInst), L);
BasePointer = dyn_cast<SCEVUnknown>(SE.getPointerBase(AccessFn));
if (BasePointer == nullptr) {
LLVM_DEBUG(
dbgs().indent(2)
<< "ERROR: failed to delinearize, can't identify base pointer\n");
return false;
}
bool IsFixedSize = false;
// Try to delinearize fixed-size arrays.
if (tryDelinearizeFixedSize(AccessFn, Subscripts)) {
IsFixedSize = true;
// The last element of Sizes is the element size.
Sizes.push_back(ElemSize);
LLVM_DEBUG(dbgs().indent(2) << "In Loop '" << L->getName()
<< "', AccessFn: " << *AccessFn << "\n");
}
AccessFn = SE.getMinusSCEV(AccessFn, BasePointer);
// Try to delinearize parametric-size arrays.
if (!IsFixedSize) {
LLVM_DEBUG(dbgs().indent(2) << "In Loop '" << L->getName()
<< "', AccessFn: " << *AccessFn << "\n");
llvm::delinearize(SE, AccessFn, Subscripts, Sizes,
SE.getElementSize(&StoreOrLoadInst));
}
if (Subscripts.empty() || Sizes.empty() ||
Subscripts.size() != Sizes.size()) {
// Attempt to determine whether we have a single dimensional array access.
// before giving up.
if (!isOneDimensionalArray(*AccessFn, *ElemSize, *L, SE)) {
LLVM_DEBUG(dbgs().indent(2)
<< "ERROR: failed to delinearize reference\n");
Subscripts.clear();
Sizes.clear();
return false;
}
// The array may be accessed in reverse, for example:
// for (i = N; i > 0; i--)
// A[i] = 0;
// In this case, reconstruct the access function using the absolute value
// of the step recurrence.
const SCEVAddRecExpr *AccessFnAR = dyn_cast<SCEVAddRecExpr>(AccessFn);
const SCEV *StepRec = AccessFnAR ? AccessFnAR->getStepRecurrence(SE) : nullptr;
if (StepRec && SE.isKnownNegative(StepRec))
AccessFn = SE.getAddRecExpr(AccessFnAR->getStart(),
SE.getNegativeSCEV(StepRec),
AccessFnAR->getLoop(),
AccessFnAR->getNoWrapFlags());
const SCEV *Div = SE.getUDivExactExpr(AccessFn, ElemSize);
Subscripts.push_back(Div);
Sizes.push_back(ElemSize);
}
return all_of(Subscripts, [&](const SCEV *Subscript) {
return isSimpleAddRecurrence(*Subscript, *L);
});
}
return false;
}
bool IndexedReference::isLoopInvariant(const Loop &L) const {
Value *Addr = getPointerOperand(&StoreOrLoadInst);
assert(Addr != nullptr && "Expecting either a load or a store instruction");
assert(SE.isSCEVable(Addr->getType()) && "Addr should be SCEVable");
if (SE.isLoopInvariant(SE.getSCEV(Addr), &L))
return true;
// The indexed reference is loop invariant if none of the coefficients use
// the loop induction variable.
bool allCoeffForLoopAreZero = all_of(Subscripts, [&](const SCEV *Subscript) {
return isCoeffForLoopZeroOrInvariant(*Subscript, L);
});
return allCoeffForLoopAreZero;
}
bool IndexedReference::isConsecutive(const Loop &L, const SCEV *&Stride,
unsigned CLS) const {
// The indexed reference is 'consecutive' if the only coefficient that uses
// the loop induction variable is the last one...
const SCEV *LastSubscript = Subscripts.back();
for (const SCEV *Subscript : Subscripts) {
if (Subscript == LastSubscript)
continue;
if (!isCoeffForLoopZeroOrInvariant(*Subscript, L))
return false;
}
// ...and the access stride is less than the cache line size.
const SCEV *Coeff = getLastCoefficient();
const SCEV *ElemSize = Sizes.back();
Type *WiderType = SE.getWiderType(Coeff->getType(), ElemSize->getType());
// FIXME: This assumes that all values are signed integers which may
// be incorrect in unusual codes and incorrectly use sext instead of zext.
// for (uint32_t i = 0; i < 512; ++i) {
// uint8_t trunc = i;
// A[trunc] = 42;
// }
// This consecutively iterates twice over A. If `trunc` is sign-extended,
// we would conclude that this may iterate backwards over the array.
// However, LoopCacheAnalysis is heuristic anyway and transformations must
// not result in wrong optimizations if the heuristic was incorrect.
Stride = SE.getMulExpr(SE.getNoopOrSignExtend(Coeff, WiderType),
SE.getNoopOrSignExtend(ElemSize, WiderType));
const SCEV *CacheLineSize = SE.getConstant(Stride->getType(), CLS);
Stride = SE.isKnownNegative(Stride) ? SE.getNegativeSCEV(Stride) : Stride;
return SE.isKnownPredicate(ICmpInst::ICMP_ULT, Stride, CacheLineSize);
}
int IndexedReference::getSubscriptIndex(const Loop &L) const {
for (auto Idx : seq<int>(0, getNumSubscripts())) {
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(getSubscript(Idx));
if (AR && AR->getLoop() == &L) {
return Idx;
}
}
return -1;
}
const SCEV *IndexedReference::getLastCoefficient() const {
const SCEV *LastSubscript = getLastSubscript();
auto *AR = cast<SCEVAddRecExpr>(LastSubscript);
return AR->getStepRecurrence(SE);
}
bool IndexedReference::isCoeffForLoopZeroOrInvariant(const SCEV &Subscript,
const Loop &L) const {
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(&Subscript);
return (AR != nullptr) ? AR->getLoop() != &L
: SE.isLoopInvariant(&Subscript, &L);
}
bool IndexedReference::isSimpleAddRecurrence(const SCEV &Subscript,
const Loop &L) const {
if (!isa<SCEVAddRecExpr>(Subscript))
return false;
const SCEVAddRecExpr *AR = cast<SCEVAddRecExpr>(&Subscript);
assert(AR->getLoop() && "AR should have a loop");
if (!AR->isAffine())
return false;
const SCEV *Start = AR->getStart();
const SCEV *Step = AR->getStepRecurrence(SE);
if (!SE.isLoopInvariant(Start, &L) || !SE.isLoopInvariant(Step, &L))
return false;
return true;
}
bool IndexedReference::isAliased(const IndexedReference &Other,
AAResults &AA) const {
const auto &Loc1 = MemoryLocation::get(&StoreOrLoadInst);
const auto &Loc2 = MemoryLocation::get(&Other.StoreOrLoadInst);
return AA.isMustAlias(Loc1, Loc2);
}
//===----------------------------------------------------------------------===//
// CacheCost implementation
//
raw_ostream &llvm::operator<<(raw_ostream &OS, const CacheCost &CC) {
for (const auto &LC : CC.LoopCosts) {
const Loop *L = LC.first;
OS << "Loop '" << L->getName() << "' has cost = " << LC.second << "\n";
}
return OS;
}
CacheCost::CacheCost(const LoopVectorTy &Loops, const LoopInfo &LI,
ScalarEvolution &SE, TargetTransformInfo &TTI,
AAResults &AA, DependenceInfo &DI, Optional<unsigned> TRT)
: Loops(Loops),
TRT((TRT == None) ? Optional<unsigned>(TemporalReuseThreshold) : TRT),
LI(LI), SE(SE), TTI(TTI), AA(AA), DI(DI) {
assert(!Loops.empty() && "Expecting a non-empty loop vector.");
for (const Loop *L : Loops) {
unsigned TripCount = SE.getSmallConstantTripCount(L);
TripCount = (TripCount == 0) ? DefaultTripCount : TripCount;
TripCounts.push_back({L, TripCount});
}
calculateCacheFootprint();
}
std::unique_ptr<CacheCost>
CacheCost::getCacheCost(Loop &Root, LoopStandardAnalysisResults &AR,
DependenceInfo &DI, Optional<unsigned> TRT) {
if (!Root.isOutermost()) {
LLVM_DEBUG(dbgs() << "Expecting the outermost loop in a loop nest\n");
return nullptr;
}
LoopVectorTy Loops;
append_range(Loops, breadth_first(&Root));
if (!getInnerMostLoop(Loops)) {
LLVM_DEBUG(dbgs() << "Cannot compute cache cost of loop nest with more "
"than one innermost loop\n");
return nullptr;
}
return std::make_unique<CacheCost>(Loops, AR.LI, AR.SE, AR.TTI, AR.AA, DI, TRT);
}
void CacheCost::calculateCacheFootprint() {
LLVM_DEBUG(dbgs() << "POPULATING REFERENCE GROUPS\n");
ReferenceGroupsTy RefGroups;
if (!populateReferenceGroups(RefGroups))
return;
LLVM_DEBUG(dbgs() << "COMPUTING LOOP CACHE COSTS\n");
for (const Loop *L : Loops) {
assert(llvm::none_of(
LoopCosts,
[L](const LoopCacheCostTy &LCC) { return LCC.first == L; }) &&
"Should not add duplicate element");
CacheCostTy LoopCost = computeLoopCacheCost(*L, RefGroups);
LoopCosts.push_back(std::make_pair(L, LoopCost));
}
sortLoopCosts();
RefGroups.clear();
}
bool CacheCost::populateReferenceGroups(ReferenceGroupsTy &RefGroups) const {
assert(RefGroups.empty() && "Reference groups should be empty");
unsigned CLS = TTI.getCacheLineSize();
Loop *InnerMostLoop = getInnerMostLoop(Loops);
assert(InnerMostLoop != nullptr && "Expecting a valid innermost loop");
for (BasicBlock *BB : InnerMostLoop->getBlocks()) {
for (Instruction &I : *BB) {
if (!isa<StoreInst>(I) && !isa<LoadInst>(I))
continue;
std::unique_ptr<IndexedReference> R(new IndexedReference(I, LI, SE));
if (!R->isValid())
continue;
bool Added = false;
for (ReferenceGroupTy &RefGroup : RefGroups) {
const IndexedReference &Representative = *RefGroup.front();
LLVM_DEBUG({
dbgs() << "References:\n";
dbgs().indent(2) << *R << "\n";
dbgs().indent(2) << Representative << "\n";
});
// FIXME: Both positive and negative access functions will be placed
// into the same reference group, resulting in a bi-directional array
// access such as:
// for (i = N; i > 0; i--)
// A[i] = A[N - i];
// having the same cost calculation as a single dimention access pattern
// for (i = 0; i < N; i++)
// A[i] = A[i];
// when in actuality, depending on the array size, the first example
// should have a cost closer to 2x the second due to the two cache
// access per iteration from opposite ends of the array
Optional<bool> HasTemporalReuse =
R->hasTemporalReuse(Representative, *TRT, *InnerMostLoop, DI, AA);
Optional<bool> HasSpacialReuse =
R->hasSpacialReuse(Representative, CLS, AA);
if ((HasTemporalReuse && *HasTemporalReuse) ||
(HasSpacialReuse && *HasSpacialReuse)) {
RefGroup.push_back(std::move(R));
Added = true;
break;
}
}
if (!Added) {
ReferenceGroupTy RG;
RG.push_back(std::move(R));
RefGroups.push_back(std::move(RG));
}
}
}
if (RefGroups.empty())
return false;
LLVM_DEBUG({
dbgs() << "\nIDENTIFIED REFERENCE GROUPS:\n";
int n = 1;
for (const ReferenceGroupTy &RG : RefGroups) {
dbgs().indent(2) << "RefGroup " << n << ":\n";
for (const auto &IR : RG)
dbgs().indent(4) << *IR << "\n";
n++;
}
dbgs() << "\n";
});
return true;
}
CacheCostTy
CacheCost::computeLoopCacheCost(const Loop &L,
const ReferenceGroupsTy &RefGroups) const {
if (!L.isLoopSimplifyForm())
return InvalidCost;
LLVM_DEBUG(dbgs() << "Considering loop '" << L.getName()
<< "' as innermost loop.\n");
// Compute the product of the trip counts of each other loop in the nest.
CacheCostTy TripCountsProduct = 1;
for (const auto &TC : TripCounts) {
if (TC.first == &L)
continue;
TripCountsProduct *= TC.second;
}
CacheCostTy LoopCost = 0;
for (const ReferenceGroupTy &RG : RefGroups) {
CacheCostTy RefGroupCost = computeRefGroupCacheCost(RG, L);
LoopCost += RefGroupCost * TripCountsProduct;
}
LLVM_DEBUG(dbgs().indent(2) << "Loop '" << L.getName()
<< "' has cost=" << LoopCost << "\n");
return LoopCost;
}
CacheCostTy CacheCost::computeRefGroupCacheCost(const ReferenceGroupTy &RG,
const Loop &L) const {
assert(!RG.empty() && "Reference group should have at least one member.");
const IndexedReference *Representative = RG.front().get();
return Representative->computeRefCost(L, TTI.getCacheLineSize());
}
//===----------------------------------------------------------------------===//
// LoopCachePrinterPass implementation
//
PreservedAnalyses LoopCachePrinterPass::run(Loop &L, LoopAnalysisManager &AM,
LoopStandardAnalysisResults &AR,
LPMUpdater &U) {
Function *F = L.getHeader()->getParent();
DependenceInfo DI(F, &AR.AA, &AR.SE, &AR.LI);
if (auto CC = CacheCost::getCacheCost(L, AR, DI))
OS << *CC;
return PreservedAnalyses::all();
}
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