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llvm-mirror/lib/Analysis/LoopAccessAnalysis.cpp
Adam Nemet 2a8bdf8474 [getUnderlyingOjbects] Analyze loop PHIs further to remove false positives 
Specifically, if a pointer accesses different underlying objects in each
iteration, don't look through the phi node defining the pointer.

The motivating case is the underlyling-objects-2.ll testcase.  Consider
the loop nest:

  int **A;
  for (i)
    for (j)
       A[i][j] = A[i-1][j] * B[j]

This loop is transformed by Load-PRE to stash away A[i] for the next
iteration of the outer loop:

  Curr = A[0];          // Prev_0
  for (i: 1..N) {
    Prev = Curr;        // Prev = PHI (Prev_0, Curr)
    Curr = A[i];
    for (j: 0..N)
       Curr[j] = Prev[j] * B[j]
  }

Since A[i] and A[i-1] are likely to be independent pointers,
getUnderlyingObjects should not assume that Curr and Prev share the same
underlying object in the inner loop.

If it did we would try to dependence-analyze Curr and Prev and the
analysis of the corresponding SCEVs would fail with non-constant
distance.

To fix this, the getUnderlyingObjects API is extended with an optional
LoopInfo parameter.  This is effectively what controls whether we want
the above behavior or the original.  Currently, I only changed to use
this approach for LoopAccessAnalysis.

The other testcase is to guard the opposite case where we do want to
look through the loop PHI.  If we step through an array by incrementing
a pointer, the underlying object is the incoming value of the phi as the
loop is entered.

Fixes rdar://problem/19566729

llvm-svn: 235634
2015-04-23 20:09:20 +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(); }
void resetDepChecks() { CheckDeps.clear(); }
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 {
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();
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";
}
OS.indent(Depth) << "Store to invariant address was "
<< (StoreToLoopInvariantAddress ? "" : "not ")
<< "found in loop.\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";
}
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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