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llvm-mirror/lib/Analysis/LoopAccessAnalysis.cpp
Adam Nemet abe4727e89 [LoopAccesses] If shouldRetryWithRuntimeCheck, reset InterestingDependences 
When dependence analysis encounters a non-constant distance between
memory accesses it aborts the analysis and falls back to run-time checks
only.  In this case we weren't resetting the array of dependences.

llvm-svn: 237574
2015-05-18 15:37:03 +00:00

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//===- LoopAccessAnalysis.cpp - Loop Access Analysis Implementation --------==//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// The implementation for the loop memory dependence that was originally
// developed for the loop vectorizer.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/LoopAccessAnalysis.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/VectorUtils.h"
using namespace llvm;
#define DEBUG_TYPE "loop-accesses"
static cl::opt<unsigned, true>
VectorizationFactor("force-vector-width", cl::Hidden,
cl::desc("Sets the SIMD width. Zero is autoselect."),
cl::location(VectorizerParams::VectorizationFactor));
unsigned VectorizerParams::VectorizationFactor;
static cl::opt<unsigned, true>
VectorizationInterleave("force-vector-interleave", cl::Hidden,
cl::desc("Sets the vectorization interleave count. "
"Zero is autoselect."),
cl::location(
VectorizerParams::VectorizationInterleave));
unsigned VectorizerParams::VectorizationInterleave;
static cl::opt<unsigned, true> RuntimeMemoryCheckThreshold(
"runtime-memory-check-threshold", cl::Hidden,
cl::desc("When performing memory disambiguation checks at runtime do not "
"generate more than this number of comparisons (default = 8)."),
cl::location(VectorizerParams::RuntimeMemoryCheckThreshold), cl::init(8));
unsigned VectorizerParams::RuntimeMemoryCheckThreshold;
/// Maximum SIMD width.
const unsigned VectorizerParams::MaxVectorWidth = 64;
/// \brief We collect interesting dependences up to this threshold.
static cl::opt<unsigned> MaxInterestingDependence(
"max-interesting-dependences", cl::Hidden,
cl::desc("Maximum number of interesting dependences collected by "
"loop-access analysis (default = 100)"),
cl::init(100));
bool VectorizerParams::isInterleaveForced() {
return ::VectorizationInterleave.getNumOccurrences() > 0;
}
void LoopAccessReport::emitAnalysis(const LoopAccessReport &Message,
const Function *TheFunction,
const Loop *TheLoop,
const char *PassName) {
DebugLoc DL = TheLoop->getStartLoc();
if (const Instruction *I = Message.getInstr())
DL = I->getDebugLoc();
emitOptimizationRemarkAnalysis(TheFunction->getContext(), PassName,
*TheFunction, DL, Message.str());
}
Value *llvm::stripIntegerCast(Value *V) {
if (CastInst *CI = dyn_cast<CastInst>(V))
if (CI->getOperand(0)->getType()->isIntegerTy())
return CI->getOperand(0);
return V;
}
const SCEV *llvm::replaceSymbolicStrideSCEV(ScalarEvolution *SE,
const ValueToValueMap &PtrToStride,
Value *Ptr, Value *OrigPtr) {
const SCEV *OrigSCEV = SE->getSCEV(Ptr);
// If there is an entry in the map return the SCEV of the pointer with the
// symbolic stride replaced by one.
ValueToValueMap::const_iterator SI =
PtrToStride.find(OrigPtr ? OrigPtr : Ptr);
if (SI != PtrToStride.end()) {
Value *StrideVal = SI->second;
// Strip casts.
StrideVal = stripIntegerCast(StrideVal);
// Replace symbolic stride by one.
Value *One = ConstantInt::get(StrideVal->getType(), 1);
ValueToValueMap RewriteMap;
RewriteMap[StrideVal] = One;
const SCEV *ByOne =
SCEVParameterRewriter::rewrite(OrigSCEV, *SE, RewriteMap, true);
DEBUG(dbgs() << "LAA: Replacing SCEV: " << *OrigSCEV << " by: " << *ByOne
<< "\n");
return ByOne;
}
// Otherwise, just return the SCEV of the original pointer.
return SE->getSCEV(Ptr);
}
void LoopAccessInfo::RuntimePointerCheck::insert(
ScalarEvolution *SE, Loop *Lp, Value *Ptr, bool WritePtr, unsigned DepSetId,
unsigned ASId, const ValueToValueMap &Strides) {
// Get the stride replaced scev.
const SCEV *Sc = replaceSymbolicStrideSCEV(SE, Strides, Ptr);
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Sc);
assert(AR && "Invalid addrec expression");
const SCEV *Ex = SE->getBackedgeTakenCount(Lp);
const SCEV *ScEnd = AR->evaluateAtIteration(Ex, *SE);
Pointers.push_back(Ptr);
Starts.push_back(AR->getStart());
Ends.push_back(ScEnd);
IsWritePtr.push_back(WritePtr);
DependencySetId.push_back(DepSetId);
AliasSetId.push_back(ASId);
}
bool LoopAccessInfo::RuntimePointerCheck::needsChecking(
unsigned I, unsigned J, const SmallVectorImpl<int> *PtrPartition) const {
// No need to check if two readonly pointers intersect.
if (!IsWritePtr[I] && !IsWritePtr[J])
return false;
// Only need to check pointers between two different dependency sets.
if (DependencySetId[I] == DependencySetId[J])
return false;
// Only need to check pointers in the same alias set.
if (AliasSetId[I] != AliasSetId[J])
return false;
// If PtrPartition is set omit checks between pointers of the same partition.
// Partition number -1 means that the pointer is used in multiple partitions.
// In this case we can't omit the check.
if (PtrPartition && (*PtrPartition)[I] != -1 &&
(*PtrPartition)[I] == (*PtrPartition)[J])
return false;
return true;
}
void LoopAccessInfo::RuntimePointerCheck::print(
raw_ostream &OS, unsigned Depth,
const SmallVectorImpl<int> *PtrPartition) const {
unsigned NumPointers = Pointers.size();
if (NumPointers == 0)
return;
OS.indent(Depth) << "Run-time memory checks:\n";
unsigned N = 0;
for (unsigned I = 0; I < NumPointers; ++I)
for (unsigned J = I + 1; J < NumPointers; ++J)
if (needsChecking(I, J, PtrPartition)) {
OS.indent(Depth) << N++ << ":\n";
OS.indent(Depth + 2) << *Pointers[I];
if (PtrPartition)
OS << " (Partition: " << (*PtrPartition)[I] << ")";
OS << "\n";
OS.indent(Depth + 2) << *Pointers[J];
if (PtrPartition)
OS << " (Partition: " << (*PtrPartition)[J] << ")";
OS << "\n";
}
}
bool LoopAccessInfo::RuntimePointerCheck::needsAnyChecking(
const SmallVectorImpl<int> *PtrPartition) const {
unsigned NumPointers = Pointers.size();
for (unsigned I = 0; I < NumPointers; ++I)
for (unsigned J = I + 1; J < NumPointers; ++J)
if (needsChecking(I, J, PtrPartition))
return true;
return false;
}
namespace {
/// \brief Analyses memory accesses in a loop.
///
/// Checks whether run time pointer checks are needed and builds sets for data
/// dependence checking.
class AccessAnalysis {
public:
/// \brief Read or write access location.
typedef PointerIntPair<Value *, 1, bool> MemAccessInfo;
typedef SmallPtrSet<MemAccessInfo, 8> MemAccessInfoSet;
AccessAnalysis(const DataLayout &Dl, AliasAnalysis *AA, LoopInfo *LI,
MemoryDepChecker::DepCandidates &DA)
: DL(Dl), AST(*AA), LI(LI), DepCands(DA), IsRTCheckNeeded(false) {}
/// \brief Register a load and whether it is only read from.
void addLoad(AliasAnalysis::Location &Loc, bool IsReadOnly) {
Value *Ptr = const_cast<Value*>(Loc.Ptr);
AST.add(Ptr, AliasAnalysis::UnknownSize, Loc.AATags);
Accesses.insert(MemAccessInfo(Ptr, false));
if (IsReadOnly)
ReadOnlyPtr.insert(Ptr);
}
/// \brief Register a store.
void addStore(AliasAnalysis::Location &Loc) {
Value *Ptr = const_cast<Value*>(Loc.Ptr);
AST.add(Ptr, AliasAnalysis::UnknownSize, Loc.AATags);
Accesses.insert(MemAccessInfo(Ptr, true));
}
/// \brief Check whether we can check the pointers at runtime for
/// non-intersection.
bool canCheckPtrAtRT(LoopAccessInfo::RuntimePointerCheck &RtCheck,
unsigned &NumComparisons, ScalarEvolution *SE,
Loop *TheLoop, const ValueToValueMap &Strides,
bool ShouldCheckStride = false);
/// \brief Goes over all memory accesses, checks whether a RT check is needed
/// and builds sets of dependent accesses.
void buildDependenceSets() {
processMemAccesses();
}
bool isRTCheckNeeded() { return IsRTCheckNeeded; }
bool isDependencyCheckNeeded() { return !CheckDeps.empty(); }
/// We decided that no dependence analysis would be used. Reset the state.
void resetDepChecks(MemoryDepChecker &DepChecker) {
CheckDeps.clear();
DepChecker.clearInterestingDependences();
}
MemAccessInfoSet &getDependenciesToCheck() { return CheckDeps; }
private:
typedef SetVector<MemAccessInfo> PtrAccessSet;
/// \brief Go over all memory access and check whether runtime pointer checks
/// are needed /// and build sets of dependency check candidates.
void processMemAccesses();
/// Set of all accesses.
PtrAccessSet Accesses;
const DataLayout &DL;
/// Set of accesses that need a further dependence check.
MemAccessInfoSet CheckDeps;
/// Set of pointers that are read only.
SmallPtrSet<Value*, 16> ReadOnlyPtr;
/// An alias set tracker to partition the access set by underlying object and
//intrinsic property (such as TBAA metadata).
AliasSetTracker AST;
LoopInfo *LI;
/// Sets of potentially dependent accesses - members of one set share an
/// underlying pointer. The set "CheckDeps" identfies which sets really need a
/// dependence check.
MemoryDepChecker::DepCandidates &DepCands;
bool IsRTCheckNeeded;
};
} // end anonymous namespace
/// \brief Check whether a pointer can participate in a runtime bounds check.
static bool hasComputableBounds(ScalarEvolution *SE,
const ValueToValueMap &Strides, Value *Ptr) {
const SCEV *PtrScev = replaceSymbolicStrideSCEV(SE, Strides, Ptr);
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev);
if (!AR)
return false;
return AR->isAffine();
}
/// \brief Check the stride of the pointer and ensure that it does not wrap in
/// the address space.
static int isStridedPtr(ScalarEvolution *SE, Value *Ptr, const Loop *Lp,
const ValueToValueMap &StridesMap);
bool AccessAnalysis::canCheckPtrAtRT(
LoopAccessInfo::RuntimePointerCheck &RtCheck, unsigned &NumComparisons,
ScalarEvolution *SE, Loop *TheLoop, const ValueToValueMap &StridesMap,
bool ShouldCheckStride) {
// Find pointers with computable bounds. We are going to use this information
// to place a runtime bound check.
bool CanDoRT = true;
bool IsDepCheckNeeded = isDependencyCheckNeeded();
NumComparisons = 0;
// We assign a consecutive id to access from different alias sets.
// Accesses between different groups doesn't need to be checked.
unsigned ASId = 1;
for (auto &AS : AST) {
unsigned NumReadPtrChecks = 0;
unsigned NumWritePtrChecks = 0;
// We assign consecutive id to access from different dependence sets.
// Accesses within the same set don't need a runtime check.
unsigned RunningDepId = 1;
DenseMap<Value *, unsigned> DepSetId;
for (auto A : AS) {
Value *Ptr = A.getValue();
bool IsWrite = Accesses.count(MemAccessInfo(Ptr, true));
MemAccessInfo Access(Ptr, IsWrite);
if (IsWrite)
++NumWritePtrChecks;
else
++NumReadPtrChecks;
if (hasComputableBounds(SE, StridesMap, Ptr) &&
// When we run after a failing dependency check we have to make sure
// we don't have wrapping pointers.
(!ShouldCheckStride ||
isStridedPtr(SE, Ptr, TheLoop, StridesMap) == 1)) {
// The id of the dependence set.
unsigned DepId;
if (IsDepCheckNeeded) {
Value *Leader = DepCands.getLeaderValue(Access).getPointer();
unsigned &LeaderId = DepSetId[Leader];
if (!LeaderId)
LeaderId = RunningDepId++;
DepId = LeaderId;
} else
// Each access has its own dependence set.
DepId = RunningDepId++;
RtCheck.insert(SE, TheLoop, Ptr, IsWrite, DepId, ASId, StridesMap);
DEBUG(dbgs() << "LAA: Found a runtime check ptr:" << *Ptr << '\n');
} else {
DEBUG(dbgs() << "LAA: Can't find bounds for ptr:" << *Ptr << '\n');
CanDoRT = false;
}
}
if (IsDepCheckNeeded && CanDoRT && RunningDepId == 2)
NumComparisons += 0; // Only one dependence set.
else {
NumComparisons += (NumWritePtrChecks * (NumReadPtrChecks +
NumWritePtrChecks - 1));
}
++ASId;
}
// If the pointers that we would use for the bounds comparison have different
// address spaces, assume the values aren't directly comparable, so we can't
// use them for the runtime check. We also have to assume they could
// overlap. In the future there should be metadata for whether address spaces
// are disjoint.
unsigned NumPointers = RtCheck.Pointers.size();
for (unsigned i = 0; i < NumPointers; ++i) {
for (unsigned j = i + 1; j < NumPointers; ++j) {
// Only need to check pointers between two different dependency sets.
if (RtCheck.DependencySetId[i] == RtCheck.DependencySetId[j])
continue;
// Only need to check pointers in the same alias set.
if (RtCheck.AliasSetId[i] != RtCheck.AliasSetId[j])
continue;
Value *PtrI = RtCheck.Pointers[i];
Value *PtrJ = RtCheck.Pointers[j];
unsigned ASi = PtrI->getType()->getPointerAddressSpace();
unsigned ASj = PtrJ->getType()->getPointerAddressSpace();
if (ASi != ASj) {
DEBUG(dbgs() << "LAA: Runtime check would require comparison between"
" different address spaces\n");
return false;
}
}
}
return CanDoRT;
}
void AccessAnalysis::processMemAccesses() {
// We process the set twice: first we process read-write pointers, last we
// process read-only pointers. This allows us to skip dependence tests for
// read-only pointers.
DEBUG(dbgs() << "LAA: Processing memory accesses...\n");
DEBUG(dbgs() << " AST: "; AST.dump());
DEBUG(dbgs() << "LAA: Accesses(" << Accesses.size() << "):\n");
DEBUG({
for (auto A : Accesses)
dbgs() << "\t" << *A.getPointer() << " (" <<
(A.getInt() ? "write" : (ReadOnlyPtr.count(A.getPointer()) ?
"read-only" : "read")) << ")\n";
});
// The AliasSetTracker has nicely partitioned our pointers by metadata
// compatibility and potential for underlying-object overlap. As a result, we
// only need to check for potential pointer dependencies within each alias
// set.
for (auto &AS : AST) {
// Note that both the alias-set tracker and the alias sets themselves used
// linked lists internally and so the iteration order here is deterministic
// (matching the original instruction order within each set).
bool SetHasWrite = false;
// Map of pointers to last access encountered.
typedef DenseMap<Value*, MemAccessInfo> UnderlyingObjToAccessMap;
UnderlyingObjToAccessMap ObjToLastAccess;
// Set of access to check after all writes have been processed.
PtrAccessSet DeferredAccesses;
// Iterate over each alias set twice, once to process read/write pointers,
// and then to process read-only pointers.
for (int SetIteration = 0; SetIteration < 2; ++SetIteration) {
bool UseDeferred = SetIteration > 0;
PtrAccessSet &S = UseDeferred ? DeferredAccesses : Accesses;
for (auto AV : AS) {
Value *Ptr = AV.getValue();
// For a single memory access in AliasSetTracker, Accesses may contain
// both read and write, and they both need to be handled for CheckDeps.
for (auto AC : S) {
if (AC.getPointer() != Ptr)
continue;
bool IsWrite = AC.getInt();
// If we're using the deferred access set, then it contains only
// reads.
bool IsReadOnlyPtr = ReadOnlyPtr.count(Ptr) && !IsWrite;
if (UseDeferred && !IsReadOnlyPtr)
continue;
// Otherwise, the pointer must be in the PtrAccessSet, either as a
// read or a write.
assert(((IsReadOnlyPtr && UseDeferred) || IsWrite ||
S.count(MemAccessInfo(Ptr, false))) &&
"Alias-set pointer not in the access set?");
MemAccessInfo Access(Ptr, IsWrite);
DepCands.insert(Access);
// Memorize read-only pointers for later processing and skip them in
// the first round (they need to be checked after we have seen all
// write pointers). Note: we also mark pointer that are not
// consecutive as "read-only" pointers (so that we check
// "a[b[i]] +="). Hence, we need the second check for "!IsWrite".
if (!UseDeferred && IsReadOnlyPtr) {
DeferredAccesses.insert(Access);
continue;
}
// If this is a write - check other reads and writes for conflicts. If
// this is a read only check other writes for conflicts (but only if
// there is no other write to the ptr - this is an optimization to
// catch "a[i] = a[i] + " without having to do a dependence check).
if ((IsWrite || IsReadOnlyPtr) && SetHasWrite) {
CheckDeps.insert(Access);
IsRTCheckNeeded = true;
}
if (IsWrite)
SetHasWrite = true;
// Create sets of pointers connected by a shared alias set and
// underlying object.
typedef SmallVector<Value *, 16> ValueVector;
ValueVector TempObjects;
GetUnderlyingObjects(Ptr, TempObjects, DL, LI);
DEBUG(dbgs() << "Underlying objects for pointer " << *Ptr << "\n");
for (Value *UnderlyingObj : TempObjects) {
UnderlyingObjToAccessMap::iterator Prev =
ObjToLastAccess.find(UnderlyingObj);
if (Prev != ObjToLastAccess.end())
DepCands.unionSets(Access, Prev->second);
ObjToLastAccess[UnderlyingObj] = Access;
DEBUG(dbgs() << " " << *UnderlyingObj << "\n");
}
}
}
}
}
}
static bool isInBoundsGep(Value *Ptr) {
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr))
return GEP->isInBounds();
return false;
}
/// \brief Check whether the access through \p Ptr has a constant stride.
static int isStridedPtr(ScalarEvolution *SE, Value *Ptr, const Loop *Lp,
const ValueToValueMap &StridesMap) {
const Type *Ty = Ptr->getType();
assert(Ty->isPointerTy() && "Unexpected non-ptr");
// Make sure that the pointer does not point to aggregate types.
const PointerType *PtrTy = cast<PointerType>(Ty);
if (PtrTy->getElementType()->isAggregateType()) {
DEBUG(dbgs() << "LAA: Bad stride - Not a pointer to a scalar type"
<< *Ptr << "\n");
return 0;
}
const SCEV *PtrScev = replaceSymbolicStrideSCEV(SE, StridesMap, Ptr);
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev);
if (!AR) {
DEBUG(dbgs() << "LAA: Bad stride - Not an AddRecExpr pointer "
<< *Ptr << " SCEV: " << *PtrScev << "\n");
return 0;
}
// The accesss function must stride over the innermost loop.
if (Lp != AR->getLoop()) {
DEBUG(dbgs() << "LAA: Bad stride - Not striding over innermost loop " <<
*Ptr << " SCEV: " << *PtrScev << "\n");
}
// The address calculation must not wrap. Otherwise, a dependence could be
// inverted.
// An inbounds getelementptr that is a AddRec with a unit stride
// cannot wrap per definition. The unit stride requirement is checked later.
// An getelementptr without an inbounds attribute and unit stride would have
// to access the pointer value "0" which is undefined behavior in address
// space 0, therefore we can also vectorize this case.
bool IsInBoundsGEP = isInBoundsGep(Ptr);
bool IsNoWrapAddRec = AR->getNoWrapFlags(SCEV::NoWrapMask);
bool IsInAddressSpaceZero = PtrTy->getAddressSpace() == 0;
if (!IsNoWrapAddRec && !IsInBoundsGEP && !IsInAddressSpaceZero) {
DEBUG(dbgs() << "LAA: Bad stride - Pointer may wrap in the address space "
<< *Ptr << " SCEV: " << *PtrScev << "\n");
return 0;
}
// Check the step is constant.
const SCEV *Step = AR->getStepRecurrence(*SE);
// Calculate the pointer stride and check if it is consecutive.
const SCEVConstant *C = dyn_cast<SCEVConstant>(Step);
if (!C) {
DEBUG(dbgs() << "LAA: Bad stride - Not a constant strided " << *Ptr <<
" SCEV: " << *PtrScev << "\n");
return 0;
}
auto &DL = Lp->getHeader()->getModule()->getDataLayout();
int64_t Size = DL.getTypeAllocSize(PtrTy->getElementType());
const APInt &APStepVal = C->getValue()->getValue();
// Huge step value - give up.
if (APStepVal.getBitWidth() > 64)
return 0;
int64_t StepVal = APStepVal.getSExtValue();
// Strided access.
int64_t Stride = StepVal / Size;
int64_t Rem = StepVal % Size;
if (Rem)
return 0;
// If the SCEV could wrap but we have an inbounds gep with a unit stride we
// know we can't "wrap around the address space". In case of address space
// zero we know that this won't happen without triggering undefined behavior.
if (!IsNoWrapAddRec && (IsInBoundsGEP || IsInAddressSpaceZero) &&
Stride != 1 && Stride != -1)
return 0;
return Stride;
}
bool MemoryDepChecker::Dependence::isSafeForVectorization(DepType Type) {
switch (Type) {
case NoDep:
case Forward:
case BackwardVectorizable:
return true;
case Unknown:
case ForwardButPreventsForwarding:
case Backward:
case BackwardVectorizableButPreventsForwarding:
return false;
}
llvm_unreachable("unexpected DepType!");
}
bool MemoryDepChecker::Dependence::isInterestingDependence(DepType Type) {
switch (Type) {
case NoDep:
case Forward:
return false;
case BackwardVectorizable:
case Unknown:
case ForwardButPreventsForwarding:
case Backward:
case BackwardVectorizableButPreventsForwarding:
return true;
}
llvm_unreachable("unexpected DepType!");
}
bool MemoryDepChecker::Dependence::isPossiblyBackward() const {
switch (Type) {
case NoDep:
case Forward:
case ForwardButPreventsForwarding:
return false;
case Unknown:
case BackwardVectorizable:
case Backward:
case BackwardVectorizableButPreventsForwarding:
return true;
}
llvm_unreachable("unexpected DepType!");
}
bool MemoryDepChecker::couldPreventStoreLoadForward(unsigned Distance,
unsigned TypeByteSize) {
// If loads occur at a distance that is not a multiple of a feasible vector
// factor store-load forwarding does not take place.
// Positive dependences might cause troubles because vectorizing them might
// prevent store-load forwarding making vectorized code run a lot slower.
// a[i] = a[i-3] ^ a[i-8];
// The stores to a[i:i+1] don't align with the stores to a[i-3:i-2] and
// hence on your typical architecture store-load forwarding does not take
// place. Vectorizing in such cases does not make sense.
// Store-load forwarding distance.
const unsigned NumCyclesForStoreLoadThroughMemory = 8*TypeByteSize;
// Maximum vector factor.
unsigned MaxVFWithoutSLForwardIssues =
VectorizerParams::MaxVectorWidth * TypeByteSize;
if(MaxSafeDepDistBytes < MaxVFWithoutSLForwardIssues)
MaxVFWithoutSLForwardIssues = MaxSafeDepDistBytes;
for (unsigned vf = 2*TypeByteSize; vf <= MaxVFWithoutSLForwardIssues;
vf *= 2) {
if (Distance % vf && Distance / vf < NumCyclesForStoreLoadThroughMemory) {
MaxVFWithoutSLForwardIssues = (vf >>=1);
break;
}
}
if (MaxVFWithoutSLForwardIssues< 2*TypeByteSize) {
DEBUG(dbgs() << "LAA: Distance " << Distance <<
" that could cause a store-load forwarding conflict\n");
return true;
}
if (MaxVFWithoutSLForwardIssues < MaxSafeDepDistBytes &&
MaxVFWithoutSLForwardIssues !=
VectorizerParams::MaxVectorWidth * TypeByteSize)
MaxSafeDepDistBytes = MaxVFWithoutSLForwardIssues;
return false;
}
MemoryDepChecker::Dependence::DepType
MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
const MemAccessInfo &B, unsigned BIdx,
const ValueToValueMap &Strides) {
assert (AIdx < BIdx && "Must pass arguments in program order");
Value *APtr = A.getPointer();
Value *BPtr = B.getPointer();
bool AIsWrite = A.getInt();
bool BIsWrite = B.getInt();
// Two reads are independent.
if (!AIsWrite && !BIsWrite)
return Dependence::NoDep;
// We cannot check pointers in different address spaces.
if (APtr->getType()->getPointerAddressSpace() !=
BPtr->getType()->getPointerAddressSpace())
return Dependence::Unknown;
const SCEV *AScev = replaceSymbolicStrideSCEV(SE, Strides, APtr);
const SCEV *BScev = replaceSymbolicStrideSCEV(SE, Strides, BPtr);
int StrideAPtr = isStridedPtr(SE, APtr, InnermostLoop, Strides);
int StrideBPtr = isStridedPtr(SE, BPtr, InnermostLoop, Strides);
const SCEV *Src = AScev;
const SCEV *Sink = BScev;
// If the induction step is negative we have to invert source and sink of the
// dependence.
if (StrideAPtr < 0) {
//Src = BScev;
//Sink = AScev;
std::swap(APtr, BPtr);
std::swap(Src, Sink);
std::swap(AIsWrite, BIsWrite);
std::swap(AIdx, BIdx);
std::swap(StrideAPtr, StrideBPtr);
}
const SCEV *Dist = SE->getMinusSCEV(Sink, Src);
DEBUG(dbgs() << "LAA: Src Scev: " << *Src << "Sink Scev: " << *Sink
<< "(Induction step: " << StrideAPtr << ")\n");
DEBUG(dbgs() << "LAA: Distance for " << *InstMap[AIdx] << " to "
<< *InstMap[BIdx] << ": " << *Dist << "\n");
// Need consecutive accesses. We don't want to vectorize
// "A[B[i]] += ..." and similar code or pointer arithmetic that could wrap in
// the address space.
if (!StrideAPtr || !StrideBPtr || StrideAPtr != StrideBPtr){
DEBUG(dbgs() << "Non-consecutive pointer access\n");
return Dependence::Unknown;
}
const SCEVConstant *C = dyn_cast<SCEVConstant>(Dist);
if (!C) {
DEBUG(dbgs() << "LAA: Dependence because of non-constant distance\n");
ShouldRetryWithRuntimeCheck = true;
return Dependence::Unknown;
}
Type *ATy = APtr->getType()->getPointerElementType();
Type *BTy = BPtr->getType()->getPointerElementType();
auto &DL = InnermostLoop->getHeader()->getModule()->getDataLayout();
unsigned TypeByteSize = DL.getTypeAllocSize(ATy);
// Negative distances are not plausible dependencies.
const APInt &Val = C->getValue()->getValue();
if (Val.isNegative()) {
bool IsTrueDataDependence = (AIsWrite && !BIsWrite);
if (IsTrueDataDependence &&
(couldPreventStoreLoadForward(Val.abs().getZExtValue(), TypeByteSize) ||
ATy != BTy))
return Dependence::ForwardButPreventsForwarding;
DEBUG(dbgs() << "LAA: Dependence is negative: NoDep\n");
return Dependence::Forward;
}
// Write to the same location with the same size.
// Could be improved to assert type sizes are the same (i32 == float, etc).
if (Val == 0) {
if (ATy == BTy)
return Dependence::NoDep;
DEBUG(dbgs() << "LAA: Zero dependence difference but different types\n");
return Dependence::Unknown;
}
assert(Val.isStrictlyPositive() && "Expect a positive value");
if (ATy != BTy) {
DEBUG(dbgs() <<
"LAA: ReadWrite-Write positive dependency with different types\n");
return Dependence::Unknown;
}
unsigned Distance = (unsigned) Val.getZExtValue();
// Bail out early if passed-in parameters make vectorization not feasible.
unsigned ForcedFactor = (VectorizerParams::VectorizationFactor ?
VectorizerParams::VectorizationFactor : 1);
unsigned ForcedUnroll = (VectorizerParams::VectorizationInterleave ?
VectorizerParams::VectorizationInterleave : 1);
// The distance must be bigger than the size needed for a vectorized version
// of the operation and the size of the vectorized operation must not be
// bigger than the currrent maximum size.
if (Distance < 2*TypeByteSize ||
2*TypeByteSize > MaxSafeDepDistBytes ||
Distance < TypeByteSize * ForcedUnroll * ForcedFactor) {
DEBUG(dbgs() << "LAA: Failure because of Positive distance "
<< Val.getSExtValue() << '\n');
return Dependence::Backward;
}
// Positive distance bigger than max vectorization factor.
MaxSafeDepDistBytes = Distance < MaxSafeDepDistBytes ?
Distance : MaxSafeDepDistBytes;
bool IsTrueDataDependence = (!AIsWrite && BIsWrite);
if (IsTrueDataDependence &&
couldPreventStoreLoadForward(Distance, TypeByteSize))
return Dependence::BackwardVectorizableButPreventsForwarding;
DEBUG(dbgs() << "LAA: Positive distance " << Val.getSExtValue() <<
" with max VF = " << MaxSafeDepDistBytes / TypeByteSize << '\n');
return Dependence::BackwardVectorizable;
}
bool MemoryDepChecker::areDepsSafe(DepCandidates &AccessSets,
MemAccessInfoSet &CheckDeps,
const ValueToValueMap &Strides) {
MaxSafeDepDistBytes = -1U;
while (!CheckDeps.empty()) {
MemAccessInfo CurAccess = *CheckDeps.begin();
// Get the relevant memory access set.
EquivalenceClasses<MemAccessInfo>::iterator I =
AccessSets.findValue(AccessSets.getLeaderValue(CurAccess));
// Check accesses within this set.
EquivalenceClasses<MemAccessInfo>::member_iterator AI, AE;
AI = AccessSets.member_begin(I), AE = AccessSets.member_end();
// Check every access pair.
while (AI != AE) {
CheckDeps.erase(*AI);
EquivalenceClasses<MemAccessInfo>::member_iterator OI = std::next(AI);
while (OI != AE) {
// Check every accessing instruction pair in program order.
for (std::vector<unsigned>::iterator I1 = Accesses[*AI].begin(),
I1E = Accesses[*AI].end(); I1 != I1E; ++I1)
for (std::vector<unsigned>::iterator I2 = Accesses[*OI].begin(),
I2E = Accesses[*OI].end(); I2 != I2E; ++I2) {
auto A = std::make_pair(&*AI, *I1);
auto B = std::make_pair(&*OI, *I2);
assert(*I1 != *I2);
if (*I1 > *I2)
std::swap(A, B);
Dependence::DepType Type =
isDependent(*A.first, A.second, *B.first, B.second, Strides);
SafeForVectorization &= Dependence::isSafeForVectorization(Type);
// Gather dependences unless we accumulated MaxInterestingDependence
// dependences. In that case return as soon as we find the first
// unsafe dependence. This puts a limit on this quadratic
// algorithm.
if (RecordInterestingDependences) {
if (Dependence::isInterestingDependence(Type))
InterestingDependences.push_back(
Dependence(A.second, B.second, Type));
if (InterestingDependences.size() >= MaxInterestingDependence) {
RecordInterestingDependences = false;
InterestingDependences.clear();
DEBUG(dbgs() << "Too many dependences, stopped recording\n");
}
}
if (!RecordInterestingDependences && !SafeForVectorization)
return false;
}
++OI;
}
AI++;
}
}
DEBUG(dbgs() << "Total Interesting Dependences: "
<< InterestingDependences.size() << "\n");
return SafeForVectorization;
}
SmallVector<Instruction *, 4>
MemoryDepChecker::getInstructionsForAccess(Value *Ptr, bool isWrite) const {
MemAccessInfo Access(Ptr, isWrite);
auto &IndexVector = Accesses.find(Access)->second;
SmallVector<Instruction *, 4> Insts;
std::transform(IndexVector.begin(), IndexVector.end(),
std::back_inserter(Insts),
[&](unsigned Idx) { return this->InstMap[Idx]; });
return Insts;
}
const char *MemoryDepChecker::Dependence::DepName[] = {
"NoDep", "Unknown", "Forward", "ForwardButPreventsForwarding", "Backward",
"BackwardVectorizable", "BackwardVectorizableButPreventsForwarding"};
void MemoryDepChecker::Dependence::print(
raw_ostream &OS, unsigned Depth,
const SmallVectorImpl<Instruction *> &Instrs) const {
OS.indent(Depth) << DepName[Type] << ":\n";
OS.indent(Depth + 2) << *Instrs[Source] << " -> \n";
OS.indent(Depth + 2) << *Instrs[Destination] << "\n";
}
bool LoopAccessInfo::canAnalyzeLoop() {
// We need to have a loop header.
DEBUG(dbgs() << "LAA: Found a loop: " <<
TheLoop->getHeader()->getName() << '\n');
// We can only analyze innermost loops.
if (!TheLoop->empty()) {
DEBUG(dbgs() << "LAA: loop is not the innermost loop\n");
emitAnalysis(LoopAccessReport() << "loop is not the innermost loop");
return false;
}
// We must have a single backedge.
if (TheLoop->getNumBackEdges() != 1) {
DEBUG(dbgs() << "LAA: loop control flow is not understood by analyzer\n");
emitAnalysis(
LoopAccessReport() <<
"loop control flow is not understood by analyzer");
return false;
}
// We must have a single exiting block.
if (!TheLoop->getExitingBlock()) {
DEBUG(dbgs() << "LAA: loop control flow is not understood by analyzer\n");
emitAnalysis(
LoopAccessReport() <<
"loop control flow is not understood by analyzer");
return false;
}
// We only handle bottom-tested loops, i.e. loop in which the condition is
// checked at the end of each iteration. With that we can assume that all
// instructions in the loop are executed the same number of times.
if (TheLoop->getExitingBlock() != TheLoop->getLoopLatch()) {
DEBUG(dbgs() << "LAA: loop control flow is not understood by analyzer\n");
emitAnalysis(
LoopAccessReport() <<
"loop control flow is not understood by analyzer");
return false;
}
// ScalarEvolution needs to be able to find the exit count.
const SCEV *ExitCount = SE->getBackedgeTakenCount(TheLoop);
if (ExitCount == SE->getCouldNotCompute()) {
emitAnalysis(LoopAccessReport() <<
"could not determine number of loop iterations");
DEBUG(dbgs() << "LAA: SCEV could not compute the loop exit count.\n");
return false;
}
return true;
}
void LoopAccessInfo::analyzeLoop(const ValueToValueMap &Strides) {
typedef SmallVector<Value*, 16> ValueVector;
typedef SmallPtrSet<Value*, 16> ValueSet;
// Holds the Load and Store *instructions*.
ValueVector Loads;
ValueVector Stores;
// Holds all the different accesses in the loop.
unsigned NumReads = 0;
unsigned NumReadWrites = 0;
PtrRtCheck.Pointers.clear();
PtrRtCheck.Need = false;
const bool IsAnnotatedParallel = TheLoop->isAnnotatedParallel();
// For each block.
for (Loop::block_iterator bb = TheLoop->block_begin(),
be = TheLoop->block_end(); bb != be; ++bb) {
// Scan the BB and collect legal loads and stores.
for (BasicBlock::iterator it = (*bb)->begin(), e = (*bb)->end(); it != e;
++it) {
// If this is a load, save it. If this instruction can read from memory
// but is not a load, then we quit. Notice that we don't handle function
// calls that read or write.
if (it->mayReadFromMemory()) {
// Many math library functions read the rounding mode. We will only
// vectorize a loop if it contains known function calls that don't set
// the flag. Therefore, it is safe to ignore this read from memory.
CallInst *Call = dyn_cast<CallInst>(it);
if (Call && getIntrinsicIDForCall(Call, TLI))
continue;
// If the function has an explicit vectorized counterpart, we can safely
// assume that it can be vectorized.
if (Call && !Call->isNoBuiltin() && Call->getCalledFunction() &&
TLI->isFunctionVectorizable(Call->getCalledFunction()->getName()))
continue;
LoadInst *Ld = dyn_cast<LoadInst>(it);
if (!Ld || (!Ld->isSimple() && !IsAnnotatedParallel)) {
emitAnalysis(LoopAccessReport(Ld)
<< "read with atomic ordering or volatile read");
DEBUG(dbgs() << "LAA: Found a non-simple load.\n");
CanVecMem = false;
return;
}
NumLoads++;
Loads.push_back(Ld);
DepChecker.addAccess(Ld);
continue;
}
// Save 'store' instructions. Abort if other instructions write to memory.
if (it->mayWriteToMemory()) {
StoreInst *St = dyn_cast<StoreInst>(it);
if (!St) {
emitAnalysis(LoopAccessReport(it) <<
"instruction cannot be vectorized");
CanVecMem = false;
return;
}
if (!St->isSimple() && !IsAnnotatedParallel) {
emitAnalysis(LoopAccessReport(St)
<< "write with atomic ordering or volatile write");
DEBUG(dbgs() << "LAA: Found a non-simple store.\n");
CanVecMem = false;
return;
}
NumStores++;
Stores.push_back(St);
DepChecker.addAccess(St);
}
} // Next instr.
} // Next block.
// Now we have two lists that hold the loads and the stores.
// Next, we find the pointers that they use.
// Check if we see any stores. If there are no stores, then we don't
// care if the pointers are *restrict*.
if (!Stores.size()) {
DEBUG(dbgs() << "LAA: Found a read-only loop!\n");
CanVecMem = true;
return;
}
MemoryDepChecker::DepCandidates DependentAccesses;
AccessAnalysis Accesses(TheLoop->getHeader()->getModule()->getDataLayout(),
AA, LI, DependentAccesses);
// Holds the analyzed pointers. We don't want to call GetUnderlyingObjects
// multiple times on the same object. If the ptr is accessed twice, once
// for read and once for write, it will only appear once (on the write
// list). This is okay, since we are going to check for conflicts between
// writes and between reads and writes, but not between reads and reads.
ValueSet Seen;
ValueVector::iterator I, IE;
for (I = Stores.begin(), IE = Stores.end(); I != IE; ++I) {
StoreInst *ST = cast<StoreInst>(*I);
Value* Ptr = ST->getPointerOperand();
// Check for store to loop invariant address.
StoreToLoopInvariantAddress |= isUniform(Ptr);
// If we did *not* see this pointer before, insert it to the read-write
// list. At this phase it is only a 'write' list.
if (Seen.insert(Ptr).second) {
++NumReadWrites;
AliasAnalysis::Location Loc = AA->getLocation(ST);
// The TBAA metadata could have a control dependency on the predication
// condition, so we cannot rely on it when determining whether or not we
// need runtime pointer checks.
if (blockNeedsPredication(ST->getParent(), TheLoop, DT))
Loc.AATags.TBAA = nullptr;
Accesses.addStore(Loc);
}
}
if (IsAnnotatedParallel) {
DEBUG(dbgs()
<< "LAA: A loop annotated parallel, ignore memory dependency "
<< "checks.\n");
CanVecMem = true;
return;
}
for (I = Loads.begin(), IE = Loads.end(); I != IE; ++I) {
LoadInst *LD = cast<LoadInst>(*I);
Value* Ptr = LD->getPointerOperand();
// If we did *not* see this pointer before, insert it to the
// read list. If we *did* see it before, then it is already in
// the read-write list. This allows us to vectorize expressions
// such as A[i] += x; Because the address of A[i] is a read-write
// pointer. This only works if the index of A[i] is consecutive.
// If the address of i is unknown (for example A[B[i]]) then we may
// read a few words, modify, and write a few words, and some of the
// words may be written to the same address.
bool IsReadOnlyPtr = false;
if (Seen.insert(Ptr).second || !isStridedPtr(SE, Ptr, TheLoop, Strides)) {
++NumReads;
IsReadOnlyPtr = true;
}
AliasAnalysis::Location Loc = AA->getLocation(LD);
// The TBAA metadata could have a control dependency on the predication
// condition, so we cannot rely on it when determining whether or not we
// need runtime pointer checks.
if (blockNeedsPredication(LD->getParent(), TheLoop, DT))
Loc.AATags.TBAA = nullptr;
Accesses.addLoad(Loc, IsReadOnlyPtr);
}
// If we write (or read-write) to a single destination and there are no
// other reads in this loop then is it safe to vectorize.
if (NumReadWrites == 1 && NumReads == 0) {
DEBUG(dbgs() << "LAA: Found a write-only loop!\n");
CanVecMem = true;
return;
}
// Build dependence sets and check whether we need a runtime pointer bounds
// check.
Accesses.buildDependenceSets();
bool NeedRTCheck = Accesses.isRTCheckNeeded();
// Find pointers with computable bounds. We are going to use this information
// to place a runtime bound check.
bool CanDoRT = false;
if (NeedRTCheck)
CanDoRT = Accesses.canCheckPtrAtRT(PtrRtCheck, NumComparisons, SE, TheLoop,
Strides);
DEBUG(dbgs() << "LAA: We need to do " << NumComparisons <<
" pointer comparisons.\n");
// If we only have one set of dependences to check pointers among we don't
// need a runtime check.
if (NumComparisons == 0 && NeedRTCheck)
NeedRTCheck = false;
// Check that we found the bounds for the pointer.
if (CanDoRT)
DEBUG(dbgs() << "LAA: We can perform a memory runtime check if needed.\n");
else if (NeedRTCheck) {
emitAnalysis(LoopAccessReport() << "cannot identify array bounds");
DEBUG(dbgs() << "LAA: We can't vectorize because we can't find " <<
"the array bounds.\n");
PtrRtCheck.reset();
CanVecMem = false;
return;
}
PtrRtCheck.Need = NeedRTCheck;
CanVecMem = true;
if (Accesses.isDependencyCheckNeeded()) {
DEBUG(dbgs() << "LAA: Checking memory dependencies\n");
CanVecMem = DepChecker.areDepsSafe(
DependentAccesses, Accesses.getDependenciesToCheck(), Strides);
MaxSafeDepDistBytes = DepChecker.getMaxSafeDepDistBytes();
if (!CanVecMem && DepChecker.shouldRetryWithRuntimeCheck()) {
DEBUG(dbgs() << "LAA: Retrying with memory checks\n");
NeedRTCheck = true;
// Clear the dependency checks. We assume they are not needed.
Accesses.resetDepChecks(DepChecker);
PtrRtCheck.reset();
PtrRtCheck.Need = true;
CanDoRT = Accesses.canCheckPtrAtRT(PtrRtCheck, NumComparisons, SE,
TheLoop, Strides, true);
// Check that we found the bounds for the pointer.
if (!CanDoRT && NumComparisons > 0) {
emitAnalysis(LoopAccessReport()
<< "cannot check memory dependencies at runtime");
DEBUG(dbgs() << "LAA: Can't vectorize with memory checks\n");
PtrRtCheck.reset();
CanVecMem = false;
return;
}
CanVecMem = true;
}
}
if (CanVecMem)
DEBUG(dbgs() << "LAA: No unsafe dependent memory operations in loop. We"
<< (NeedRTCheck ? "" : " don't")
<< " need a runtime memory check.\n");
else {
emitAnalysis(LoopAccessReport() <<
"unsafe dependent memory operations in loop");
DEBUG(dbgs() << "LAA: unsafe dependent memory operations in loop\n");
}
}
bool LoopAccessInfo::blockNeedsPredication(BasicBlock *BB, Loop *TheLoop,
DominatorTree *DT) {
assert(TheLoop->contains(BB) && "Unknown block used");
// Blocks that do not dominate the latch need predication.
BasicBlock* Latch = TheLoop->getLoopLatch();
return !DT->dominates(BB, Latch);
}
void LoopAccessInfo::emitAnalysis(LoopAccessReport &Message) {
assert(!Report && "Multiple reports generated");
Report = Message;
}
bool LoopAccessInfo::isUniform(Value *V) const {
return (SE->isLoopInvariant(SE->getSCEV(V), TheLoop));
}
// FIXME: this function is currently a duplicate of the one in
// LoopVectorize.cpp.
static Instruction *getFirstInst(Instruction *FirstInst, Value *V,
Instruction *Loc) {
if (FirstInst)
return FirstInst;
if (Instruction *I = dyn_cast<Instruction>(V))
return I->getParent() == Loc->getParent() ? I : nullptr;
return nullptr;
}
std::pair<Instruction *, Instruction *> LoopAccessInfo::addRuntimeCheck(
Instruction *Loc, const SmallVectorImpl<int> *PtrPartition) const {
if (!PtrRtCheck.Need)
return std::make_pair(nullptr, nullptr);
unsigned NumPointers = PtrRtCheck.Pointers.size();
SmallVector<TrackingVH<Value> , 2> Starts;
SmallVector<TrackingVH<Value> , 2> Ends;
LLVMContext &Ctx = Loc->getContext();
SCEVExpander Exp(*SE, DL, "induction");
Instruction *FirstInst = nullptr;
for (unsigned i = 0; i < NumPointers; ++i) {
Value *Ptr = PtrRtCheck.Pointers[i];
const SCEV *Sc = SE->getSCEV(Ptr);
if (SE->isLoopInvariant(Sc, TheLoop)) {
DEBUG(dbgs() << "LAA: Adding RT check for a loop invariant ptr:" <<
*Ptr <<"\n");
Starts.push_back(Ptr);
Ends.push_back(Ptr);
} else {
DEBUG(dbgs() << "LAA: Adding RT check for range:" << *Ptr << '\n');
unsigned AS = Ptr->getType()->getPointerAddressSpace();
// Use this type for pointer arithmetic.
Type *PtrArithTy = Type::getInt8PtrTy(Ctx, AS);
Value *Start = Exp.expandCodeFor(PtrRtCheck.Starts[i], PtrArithTy, Loc);
Value *End = Exp.expandCodeFor(PtrRtCheck.Ends[i], PtrArithTy, Loc);
Starts.push_back(Start);
Ends.push_back(End);
}
}
IRBuilder<> ChkBuilder(Loc);
// Our instructions might fold to a constant.
Value *MemoryRuntimeCheck = nullptr;
for (unsigned i = 0; i < NumPointers; ++i) {
for (unsigned j = i+1; j < NumPointers; ++j) {
if (!PtrRtCheck.needsChecking(i, j, PtrPartition))
continue;
unsigned AS0 = Starts[i]->getType()->getPointerAddressSpace();
unsigned AS1 = Starts[j]->getType()->getPointerAddressSpace();
assert((AS0 == Ends[j]->getType()->getPointerAddressSpace()) &&
(AS1 == Ends[i]->getType()->getPointerAddressSpace()) &&
"Trying to bounds check pointers with different address spaces");
Type *PtrArithTy0 = Type::getInt8PtrTy(Ctx, AS0);
Type *PtrArithTy1 = Type::getInt8PtrTy(Ctx, AS1);
Value *Start0 = ChkBuilder.CreateBitCast(Starts[i], PtrArithTy0, "bc");
Value *Start1 = ChkBuilder.CreateBitCast(Starts[j], PtrArithTy1, "bc");
Value *End0 = ChkBuilder.CreateBitCast(Ends[i], PtrArithTy1, "bc");
Value *End1 = ChkBuilder.CreateBitCast(Ends[j], PtrArithTy0, "bc");
Value *Cmp0 = ChkBuilder.CreateICmpULE(Start0, End1, "bound0");
FirstInst = getFirstInst(FirstInst, Cmp0, Loc);
Value *Cmp1 = ChkBuilder.CreateICmpULE(Start1, End0, "bound1");
FirstInst = getFirstInst(FirstInst, Cmp1, Loc);
Value *IsConflict = ChkBuilder.CreateAnd(Cmp0, Cmp1, "found.conflict");
FirstInst = getFirstInst(FirstInst, IsConflict, Loc);
if (MemoryRuntimeCheck) {
IsConflict = ChkBuilder.CreateOr(MemoryRuntimeCheck, IsConflict,
"conflict.rdx");
FirstInst = getFirstInst(FirstInst, IsConflict, Loc);
}
MemoryRuntimeCheck = IsConflict;
}
}
if (!MemoryRuntimeCheck)
return std::make_pair(nullptr, nullptr);
// We have to do this trickery because the IRBuilder might fold the check to a
// constant expression in which case there is no Instruction anchored in a
// the block.
Instruction *Check = BinaryOperator::CreateAnd(MemoryRuntimeCheck,
ConstantInt::getTrue(Ctx));
ChkBuilder.Insert(Check, "memcheck.conflict");
FirstInst = getFirstInst(FirstInst, Check, Loc);
return std::make_pair(FirstInst, Check);
}
LoopAccessInfo::LoopAccessInfo(Loop *L, ScalarEvolution *SE,
const DataLayout &DL,
const TargetLibraryInfo *TLI, AliasAnalysis *AA,
DominatorTree *DT, LoopInfo *LI,
const ValueToValueMap &Strides)
: DepChecker(SE, L), NumComparisons(0), TheLoop(L), SE(SE), DL(DL),
TLI(TLI), AA(AA), DT(DT), LI(LI), NumLoads(0), NumStores(0),
MaxSafeDepDistBytes(-1U), CanVecMem(false),
StoreToLoopInvariantAddress(false) {
if (canAnalyzeLoop())
analyzeLoop(Strides);
}
void LoopAccessInfo::print(raw_ostream &OS, unsigned Depth) const {
if (CanVecMem) {
if (PtrRtCheck.Need)
OS.indent(Depth) << "Memory dependences are safe with run-time checks\n";
else
OS.indent(Depth) << "Memory dependences are safe\n";
}
if (Report)
OS.indent(Depth) << "Report: " << Report->str() << "\n";
if (auto *InterestingDependences = DepChecker.getInterestingDependences()) {
OS.indent(Depth) << "Interesting Dependences:\n";
for (auto &Dep : *InterestingDependences) {
Dep.print(OS, Depth + 2, DepChecker.getMemoryInstructions());
OS << "\n";
}
} else
OS.indent(Depth) << "Too many interesting dependences, not recorded\n";
// List the pair of accesses need run-time checks to prove independence.
PtrRtCheck.print(OS, Depth);
OS << "\n";
OS.indent(Depth) << "Store to invariant address was "
<< (StoreToLoopInvariantAddress ? "" : "not ")
<< "found in loop.\n";
}
const LoopAccessInfo &
LoopAccessAnalysis::getInfo(Loop *L, const ValueToValueMap &Strides) {
auto &LAI = LoopAccessInfoMap[L];
#ifndef NDEBUG
assert((!LAI || LAI->NumSymbolicStrides == Strides.size()) &&
"Symbolic strides changed for loop");
#endif
if (!LAI) {
const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
LAI = llvm::make_unique<LoopAccessInfo>(L, SE, DL, TLI, AA, DT, LI,
Strides);
#ifndef NDEBUG
LAI->NumSymbolicStrides = Strides.size();
#endif
}
return *LAI.get();
}
void LoopAccessAnalysis::print(raw_ostream &OS, const Module *M) const {
LoopAccessAnalysis &LAA = *const_cast<LoopAccessAnalysis *>(this);
ValueToValueMap NoSymbolicStrides;
for (Loop *TopLevelLoop : *LI)
for (Loop *L : depth_first(TopLevelLoop)) {
OS.indent(2) << L->getHeader()->getName() << ":\n";
auto &LAI = LAA.getInfo(L, NoSymbolicStrides);
LAI.print(OS, 4);
}
}
bool LoopAccessAnalysis::runOnFunction(Function &F) {
SE = &getAnalysis<ScalarEvolution>();
auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
TLI = TLIP ? &TLIP->getTLI() : nullptr;
AA = &getAnalysis<AliasAnalysis>();
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
return false;
}
void LoopAccessAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<ScalarEvolution>();
AU.addRequired<AliasAnalysis>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<LoopInfoWrapperPass>();
AU.setPreservesAll();
}
char LoopAccessAnalysis::ID = 0;
static const char laa_name[] = "Loop Access Analysis";
#define LAA_NAME "loop-accesses"
INITIALIZE_PASS_BEGIN(LoopAccessAnalysis, LAA_NAME, laa_name, false, true)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
INITIALIZE_PASS_END(LoopAccessAnalysis, LAA_NAME, laa_name, false, true)
namespace llvm {
Pass *createLAAPass() {
return new LoopAccessAnalysis();
}
}
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