[llvm] r227756 - [LoopVectorize] Move LoopAccessAnalysis to its own module
Adam Nemet
anemet at apple.com
Sun Feb 1 08:56:15 PST 2015
Author: anemet
Date: Sun Feb 1 10:56:15 2015
New Revision: 227756
URL: http://llvm.org/viewvc/llvm-project?rev=227756&view=rev
Log:
[LoopVectorize] Move LoopAccessAnalysis to its own module
Other than moving code and adding the boilerplate for the new files, the code
being moved is unchanged.
There are a few global functions that are shared with the rest of the
LoopVectorizer. I moved these to the new module as well (emitLoopAnalysis,
stripIntegerCast, replaceSymbolicStrideSCEV) along with the Report class used
by emitLoopAnalysis. There is probably room for further improvement in this
area.
I kept DEBUG_TYPE "loop-vectorize" because it's used as the PassName with
emitOptimizationRemarkAnalysis. This will obviously have to change.
NFC. This is part of the patchset that splits out the memory dependence logic
from LoopVectorizationLegality into a new class LoopAccessAnalysis.
LoopAccessAnalysis will be used by the new Loop Distribution pass.
Added:
llvm/trunk/include/llvm/Analysis/LoopAccessAnalysis.h
llvm/trunk/lib/Analysis/LoopAccessAnalysis.cpp
Modified:
llvm/trunk/lib/Analysis/CMakeLists.txt
llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
Added: llvm/trunk/include/llvm/Analysis/LoopAccessAnalysis.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/LoopAccessAnalysis.h?rev=227756&view=auto
==============================================================================
--- llvm/trunk/include/llvm/Analysis/LoopAccessAnalysis.h (added)
+++ llvm/trunk/include/llvm/Analysis/LoopAccessAnalysis.h Sun Feb 1 10:56:15 2015
@@ -0,0 +1,201 @@
+//===- llvm/Analysis/LoopAccessAnalysis.h -----------------------*- C++ -*-===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the interface for the loop memory dependence framework that
+// was originally developed for the Loop Vectorizer.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_LOOPACCESSANALYSIS_H
+#define LLVM_ANALYSIS_LOOPACCESSANALYSIS_H
+
+#include "llvm/ADT/EquivalenceClasses.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/AliasSetTracker.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/IR/ValueHandle.h"
+#include "llvm/Support/raw_ostream.h"
+
+namespace llvm {
+
+class Value;
+class DataLayout;
+class AliasAnalysis;
+class ScalarEvolution;
+class Loop;
+class SCEV;
+
+/// Optimization analysis message produced during vectorization. Messages inform
+/// the user why vectorization did not occur.
+class VectorizationReport {
+ std::string Message;
+ raw_string_ostream Out;
+ Instruction *Instr;
+
+public:
+ VectorizationReport(Instruction *I = nullptr) : Out(Message), Instr(I) {
+ Out << "loop not vectorized: ";
+ }
+
+ template <typename A> VectorizationReport &operator<<(const A &Value) {
+ Out << Value;
+ return *this;
+ }
+
+ Instruction *getInstr() { return Instr; }
+
+ std::string &str() { return Out.str(); }
+ operator Twine() { return Out.str(); }
+
+ /// \brief Emit an analysis note with the debug location from the instruction
+ /// in \p Message if available. Otherwise use the location of \p TheLoop.
+ static void emitAnalysis(VectorizationReport &Message,
+ const Function *TheFunction,
+ const Loop *TheLoop);
+};
+
+/// \brief Drive the analysis of memory accesses in the loop
+///
+/// This class is responsible for analyzing the memory accesses of a loop. It
+/// collects the accesses and then its main helper the AccessAnalysis class
+/// finds and categorizes the dependences in buildDependenceSets.
+///
+/// For memory dependences that can be analyzed at compile time, it determines
+/// whether the dependence is part of cycle inhibiting vectorization. This work
+/// is delegated to the MemoryDepChecker class.
+///
+/// For memory dependences that cannot be determined at compile time, it
+/// generates run-time checks to prove independence. This is done by
+/// AccessAnalysis::canCheckPtrAtRT and the checks are maintained by the
+/// RuntimePointerCheck class.
+class LoopAccessAnalysis {
+public:
+ /// \brief Collection of parameters used from the vectorizer.
+ struct VectorizerParams {
+ /// \brief Maximum simd width.
+ unsigned MaxVectorWidth;
+
+ /// \brief VF as overridden by the user.
+ unsigned VectorizationFactor;
+ /// \brief Interleave factor as overridden by the user.
+ unsigned VectorizationInterleave;
+
+ /// \\brief When performing memory disambiguation checks at runtime do not
+ /// make more than this number of comparisons.
+ unsigned RuntimeMemoryCheckThreshold;
+
+ VectorizerParams(unsigned MaxVectorWidth,
+ unsigned VectorizationFactor,
+ unsigned VectorizationInterleave,
+ unsigned RuntimeMemoryCheckThreshold) :
+ MaxVectorWidth(MaxVectorWidth),
+ VectorizationFactor(VectorizationFactor),
+ VectorizationInterleave(VectorizationInterleave),
+ RuntimeMemoryCheckThreshold(RuntimeMemoryCheckThreshold) {}
+ };
+
+ /// This struct holds information about the memory runtime legality check that
+ /// a group of pointers do not overlap.
+ struct RuntimePointerCheck {
+ RuntimePointerCheck() : Need(false) {}
+
+ /// Reset the state of the pointer runtime information.
+ void reset() {
+ Need = false;
+ Pointers.clear();
+ Starts.clear();
+ Ends.clear();
+ IsWritePtr.clear();
+ DependencySetId.clear();
+ AliasSetId.clear();
+ }
+
+ /// Insert a pointer and calculate the start and end SCEVs.
+ void insert(ScalarEvolution *SE, Loop *Lp, Value *Ptr, bool WritePtr,
+ unsigned DepSetId, unsigned ASId, ValueToValueMap &Strides);
+
+ /// This flag indicates if we need to add the runtime check.
+ bool Need;
+ /// Holds the pointers that we need to check.
+ SmallVector<TrackingVH<Value>, 2> Pointers;
+ /// Holds the pointer value at the beginning of the loop.
+ SmallVector<const SCEV*, 2> Starts;
+ /// Holds the pointer value at the end of the loop.
+ SmallVector<const SCEV*, 2> Ends;
+ /// Holds the information if this pointer is used for writing to memory.
+ SmallVector<bool, 2> IsWritePtr;
+ /// Holds the id of the set of pointers that could be dependent because of a
+ /// shared underlying object.
+ SmallVector<unsigned, 2> DependencySetId;
+ /// Holds the id of the disjoint alias set to which this pointer belongs.
+ SmallVector<unsigned, 2> AliasSetId;
+ };
+
+ LoopAccessAnalysis(Function *F, Loop *L, ScalarEvolution *SE,
+ const DataLayout *DL, const TargetLibraryInfo *TLI,
+ AliasAnalysis *AA, DominatorTree *DT,
+ const VectorizerParams &VectParams) :
+ TheFunction(F), TheLoop(L), SE(SE), DL(DL), TLI(TLI), AA(AA), DT(DT),
+ NumLoads(0), NumStores(0), MaxSafeDepDistBytes(-1U),
+ VectParams(VectParams) {}
+
+ /// Return true we can analyze the memory accesses in the loop and there are
+ /// no memory dependence cycles. Replaces symbolic strides using Strides.
+ bool canVectorizeMemory(ValueToValueMap &Strides);
+
+ RuntimePointerCheck *getRuntimePointerCheck() { return &PtrRtCheck; }
+
+ /// Return true if the block BB needs to be predicated in order for the loop
+ /// to be vectorized.
+ bool blockNeedsPredication(BasicBlock *BB);
+
+ /// Returns true if the value V is uniform within the loop.
+ bool isUniform(Value *V);
+
+ unsigned getMaxSafeDepDistBytes() { return MaxSafeDepDistBytes; }
+
+private:
+ void emitAnalysis(VectorizationReport &Message);
+
+ /// We need to check that all of the pointers in this list are disjoint
+ /// at runtime.
+ RuntimePointerCheck PtrRtCheck;
+ Function *TheFunction;
+ Loop *TheLoop;
+ ScalarEvolution *SE;
+ const DataLayout *DL;
+ const TargetLibraryInfo *TLI;
+ AliasAnalysis *AA;
+ DominatorTree *DT;
+
+ unsigned NumLoads;
+ unsigned NumStores;
+
+ unsigned MaxSafeDepDistBytes;
+
+ /// \brief Vectorizer parameters used by the analysis.
+ VectorizerParams VectParams;
+};
+
+Value *stripIntegerCast(Value *V);
+
+///\brief Return the SCEV corresponding to a pointer with the symbolic stride
+///replaced with constant one.
+///
+/// If \p OrigPtr is not null, use it to look up the stride value instead of \p
+/// Ptr. \p PtrToStride provides the mapping between the pointer value and its
+/// stride as collected by LoopVectorizationLegality::collectStridedAccess.
+const SCEV *replaceSymbolicStrideSCEV(ScalarEvolution *SE,
+ ValueToValueMap &PtrToStride,
+ Value *Ptr, Value *OrigPtr = nullptr);
+
+} // End llvm namespace
+
+#endif
Modified: llvm/trunk/lib/Analysis/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/CMakeLists.txt?rev=227756&r1=227755&r2=227756&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/CMakeLists.txt (original)
+++ llvm/trunk/lib/Analysis/CMakeLists.txt Sun Feb 1 10:56:15 2015
@@ -34,6 +34,7 @@ add_llvm_library(LLVMAnalysis
LibCallSemantics.cpp
Lint.cpp
Loads.cpp
+ LoopAccessAnalysis.cpp
LoopInfo.cpp
LoopPass.cpp
MemDepPrinter.cpp
Added: llvm/trunk/lib/Analysis/LoopAccessAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/LoopAccessAnalysis.cpp?rev=227756&view=auto
==============================================================================
--- llvm/trunk/lib/Analysis/LoopAccessAnalysis.cpp (added)
+++ llvm/trunk/lib/Analysis/LoopAccessAnalysis.cpp Sun Feb 1 10:56:15 2015
@@ -0,0 +1,1084 @@
+//===- 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/ValueTracking.h"
+#include "llvm/IR/DiagnosticInfo.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Transforms/Utils/VectorUtils.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "loop-vectorize"
+
+void VectorizationReport::emitAnalysis(VectorizationReport &Message,
+ const Function *TheFunction,
+ const Loop *TheLoop) {
+ DebugLoc DL = TheLoop->getStartLoc();
+ if (Instruction *I = Message.getInstr())
+ DL = I->getDebugLoc();
+ emitOptimizationRemarkAnalysis(TheFunction->getContext(), DEBUG_TYPE,
+ *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,
+ 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::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() << "LV: Replacing SCEV: " << *OrigSCEV << " by: " << *ByOne
+ << "\n");
+ return ByOne;
+ }
+
+ // Otherwise, just return the SCEV of the original pointer.
+ return SE->getSCEV(Ptr);
+}
+
+void LoopAccessAnalysis::RuntimePointerCheck::insert(ScalarEvolution *SE,
+ Loop *Lp, Value *Ptr,
+ bool WritePtr,
+ unsigned DepSetId,
+ unsigned ASId,
+ 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);
+}
+
+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;
+
+ /// \brief Set of potential dependent memory accesses.
+ typedef EquivalenceClasses<MemAccessInfo> DepCandidates;
+
+ AccessAnalysis(const DataLayout *Dl, AliasAnalysis *AA, DepCandidates &DA) :
+ DL(Dl), AST(*AA), 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(LoopAccessAnalysis::RuntimePointerCheck &RtCheck,
+ unsigned &NumComparisons,
+ ScalarEvolution *SE, Loop *TheLoop,
+ 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;
+
+ /// Set of accesses that need a further dependence check.
+ MemAccessInfoSet CheckDeps;
+
+ /// Set of pointers that are read only.
+ SmallPtrSet<Value*, 16> ReadOnlyPtr;
+
+ const DataLayout *DL;
+
+ /// An alias set tracker to partition the access set by underlying object and
+ //intrinsic property (such as TBAA metadata).
+ AliasSetTracker AST;
+
+ /// Sets of potentially dependent accesses - members of one set share an
+ /// underlying pointer. The set "CheckDeps" identfies which sets really need a
+ /// dependence check.
+ DepCandidates &DepCands;
+
+ bool IsRTCheckNeeded;
+};
+
+} // end anonymous namespace
+
+/// \brief Check whether a pointer can participate in a runtime bounds check.
+static bool hasComputableBounds(ScalarEvolution *SE, 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, const DataLayout *DL, Value *Ptr,
+ const Loop *Lp, ValueToValueMap &StridesMap);
+
+bool AccessAnalysis::canCheckPtrAtRT(
+ LoopAccessAnalysis::RuntimePointerCheck &RtCheck,
+ unsigned &NumComparisons, ScalarEvolution *SE, Loop *TheLoop,
+ 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, DL, 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() << "LV: 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() << "LV: 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() << "LV: Processing memory accesses...\n");
+ DEBUG(dbgs() << " AST: "; AST.dump());
+ DEBUG(dbgs() << "LV: Accesses:\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);
+ for (Value *UnderlyingObj : TempObjects) {
+ UnderlyingObjToAccessMap::iterator Prev =
+ ObjToLastAccess.find(UnderlyingObj);
+ if (Prev != ObjToLastAccess.end())
+ DepCands.unionSets(Access, Prev->second);
+
+ ObjToLastAccess[UnderlyingObj] = Access;
+ }
+ }
+ }
+ }
+ }
+}
+
+namespace {
+/// \brief Checks memory dependences among accesses to the same underlying
+/// object to determine whether there vectorization is legal or not (and at
+/// which vectorization factor).
+///
+/// This class works under the assumption that we already checked that memory
+/// locations with different underlying pointers are "must-not alias".
+/// We use the ScalarEvolution framework to symbolically evalutate access
+/// functions pairs. Since we currently don't restructure the loop we can rely
+/// on the program order of memory accesses to determine their safety.
+/// At the moment we will only deem accesses as safe for:
+/// * A negative constant distance assuming program order.
+///
+/// Safe: tmp = a[i + 1]; OR a[i + 1] = x;
+/// a[i] = tmp; y = a[i];
+///
+/// The latter case is safe because later checks guarantuee that there can't
+/// be a cycle through a phi node (that is, we check that "x" and "y" is not
+/// the same variable: a header phi can only be an induction or a reduction, a
+/// reduction can't have a memory sink, an induction can't have a memory
+/// source). This is important and must not be violated (or we have to
+/// resort to checking for cycles through memory).
+///
+/// * A positive constant distance assuming program order that is bigger
+/// than the biggest memory access.
+///
+/// tmp = a[i] OR b[i] = x
+/// a[i+2] = tmp y = b[i+2];
+///
+/// Safe distance: 2 x sizeof(a[0]), and 2 x sizeof(b[0]), respectively.
+///
+/// * Zero distances and all accesses have the same size.
+///
+class MemoryDepChecker {
+public:
+ typedef PointerIntPair<Value *, 1, bool> MemAccessInfo;
+ typedef SmallPtrSet<MemAccessInfo, 8> MemAccessInfoSet;
+
+ MemoryDepChecker(ScalarEvolution *Se, const DataLayout *Dl, const Loop *L,
+ const LoopAccessAnalysis::VectorizerParams &VectParams)
+ : SE(Se), DL(Dl), InnermostLoop(L), AccessIdx(0),
+ ShouldRetryWithRuntimeCheck(false), VectParams(VectParams) {}
+
+ /// \brief Register the location (instructions are given increasing numbers)
+ /// of a write access.
+ void addAccess(StoreInst *SI) {
+ Value *Ptr = SI->getPointerOperand();
+ Accesses[MemAccessInfo(Ptr, true)].push_back(AccessIdx);
+ InstMap.push_back(SI);
+ ++AccessIdx;
+ }
+
+ /// \brief Register the location (instructions are given increasing numbers)
+ /// of a write access.
+ void addAccess(LoadInst *LI) {
+ Value *Ptr = LI->getPointerOperand();
+ Accesses[MemAccessInfo(Ptr, false)].push_back(AccessIdx);
+ InstMap.push_back(LI);
+ ++AccessIdx;
+ }
+
+ /// \brief Check whether the dependencies between the accesses are safe.
+ ///
+ /// Only checks sets with elements in \p CheckDeps.
+ bool areDepsSafe(AccessAnalysis::DepCandidates &AccessSets,
+ MemAccessInfoSet &CheckDeps, ValueToValueMap &Strides);
+
+ /// \brief The maximum number of bytes of a vector register we can vectorize
+ /// the accesses safely with.
+ unsigned getMaxSafeDepDistBytes() { return MaxSafeDepDistBytes; }
+
+ /// \brief In same cases when the dependency check fails we can still
+ /// vectorize the loop with a dynamic array access check.
+ bool shouldRetryWithRuntimeCheck() { return ShouldRetryWithRuntimeCheck; }
+
+private:
+ ScalarEvolution *SE;
+ const DataLayout *DL;
+ const Loop *InnermostLoop;
+
+ /// \brief Maps access locations (ptr, read/write) to program order.
+ DenseMap<MemAccessInfo, std::vector<unsigned> > Accesses;
+
+ /// \brief Memory access instructions in program order.
+ SmallVector<Instruction *, 16> InstMap;
+
+ /// \brief The program order index to be used for the next instruction.
+ unsigned AccessIdx;
+
+ // We can access this many bytes in parallel safely.
+ unsigned MaxSafeDepDistBytes;
+
+ /// \brief If we see a non-constant dependence distance we can still try to
+ /// vectorize this loop with runtime checks.
+ bool ShouldRetryWithRuntimeCheck;
+
+ /// \brief Vectorizer parameters used by the analysis.
+ LoopAccessAnalysis::VectorizerParams VectParams;
+
+ /// \brief Check whether there is a plausible dependence between the two
+ /// accesses.
+ ///
+ /// Access \p A must happen before \p B in program order. The two indices
+ /// identify the index into the program order map.
+ ///
+ /// This function checks whether there is a plausible dependence (or the
+ /// absence of such can't be proved) between the two accesses. If there is a
+ /// plausible dependence but the dependence distance is bigger than one
+ /// element access it records this distance in \p MaxSafeDepDistBytes (if this
+ /// distance is smaller than any other distance encountered so far).
+ /// Otherwise, this function returns true signaling a possible dependence.
+ bool isDependent(const MemAccessInfo &A, unsigned AIdx,
+ const MemAccessInfo &B, unsigned BIdx,
+ ValueToValueMap &Strides);
+
+ /// \brief Check whether the data dependence could prevent store-load
+ /// forwarding.
+ bool couldPreventStoreLoadForward(unsigned Distance, unsigned TypeByteSize);
+};
+
+} // end anonymous namespace
+
+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, const DataLayout *DL, Value *Ptr,
+ const Loop *Lp, 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() << "LV: 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() << "LV: 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() << "LV: 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() << "LV: 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() << "LV: Bad stride - Not a constant strided " << *Ptr <<
+ " SCEV: " << *PtrScev << "\n");
+ return 0;
+ }
+
+ 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::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 = VectParams.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() << "LV: Distance " << Distance <<
+ " that could cause a store-load forwarding conflict\n");
+ return true;
+ }
+
+ if (MaxVFWithoutSLForwardIssues < MaxSafeDepDistBytes &&
+ MaxVFWithoutSLForwardIssues != VectParams.MaxVectorWidth*TypeByteSize)
+ MaxSafeDepDistBytes = MaxVFWithoutSLForwardIssues;
+ return false;
+}
+
+bool MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
+ const MemAccessInfo &B, unsigned BIdx,
+ 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 false;
+
+ // We cannot check pointers in different address spaces.
+ if (APtr->getType()->getPointerAddressSpace() !=
+ BPtr->getType()->getPointerAddressSpace())
+ return true;
+
+ const SCEV *AScev = replaceSymbolicStrideSCEV(SE, Strides, APtr);
+ const SCEV *BScev = replaceSymbolicStrideSCEV(SE, Strides, BPtr);
+
+ int StrideAPtr = isStridedPtr(SE, DL, APtr, InnermostLoop, Strides);
+ int StrideBPtr = isStridedPtr(SE, DL, 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() << "LV: Src Scev: " << *Src << "Sink Scev: " << *Sink
+ << "(Induction step: " << StrideAPtr << ")\n");
+ DEBUG(dbgs() << "LV: 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 true;
+ }
+
+ const SCEVConstant *C = dyn_cast<SCEVConstant>(Dist);
+ if (!C) {
+ DEBUG(dbgs() << "LV: Dependence because of non-constant distance\n");
+ ShouldRetryWithRuntimeCheck = true;
+ return true;
+ }
+
+ Type *ATy = APtr->getType()->getPointerElementType();
+ Type *BTy = BPtr->getType()->getPointerElementType();
+ 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 true;
+
+ DEBUG(dbgs() << "LV: Dependence is negative: NoDep\n");
+ return false;
+ }
+
+ // 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 false;
+ DEBUG(dbgs() << "LV: Zero dependence difference but different types\n");
+ return true;
+ }
+
+ assert(Val.isStrictlyPositive() && "Expect a positive value");
+
+ // Positive distance bigger than max vectorization factor.
+ if (ATy != BTy) {
+ DEBUG(dbgs() <<
+ "LV: ReadWrite-Write positive dependency with different types\n");
+ return false;
+ }
+
+ unsigned Distance = (unsigned) Val.getZExtValue();
+
+ // Bail out early if passed-in parameters make vectorization not feasible.
+ unsigned ForcedFactor = (VectParams.VectorizationFactor ?
+ VectParams.VectorizationFactor : 1);
+ unsigned ForcedUnroll = (VectParams.VectorizationInterleave ?
+ VectParams.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() << "LV: Failure because of Positive distance "
+ << Val.getSExtValue() << '\n');
+ return true;
+ }
+
+ MaxSafeDepDistBytes = Distance < MaxSafeDepDistBytes ?
+ Distance : MaxSafeDepDistBytes;
+
+ bool IsTrueDataDependence = (!AIsWrite && BIsWrite);
+ if (IsTrueDataDependence &&
+ couldPreventStoreLoadForward(Distance, TypeByteSize))
+ return true;
+
+ DEBUG(dbgs() << "LV: Positive distance " << Val.getSExtValue() <<
+ " with max VF = " << MaxSafeDepDistBytes / TypeByteSize << '\n');
+
+ return false;
+}
+
+bool MemoryDepChecker::areDepsSafe(AccessAnalysis::DepCandidates &AccessSets,
+ MemAccessInfoSet &CheckDeps,
+ 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) {
+ if (*I1 < *I2 && isDependent(*AI, *I1, *OI, *I2, Strides))
+ return false;
+ if (*I2 < *I1 && isDependent(*OI, *I2, *AI, *I1, Strides))
+ return false;
+ }
+ ++OI;
+ }
+ AI++;
+ }
+ }
+ return true;
+}
+
+bool LoopAccessAnalysis::canVectorizeMemory(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();
+ MemoryDepChecker DepChecker(SE, DL, TheLoop, VectParams);
+
+ // 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;
+
+ LoadInst *Ld = dyn_cast<LoadInst>(it);
+ if (!Ld || (!Ld->isSimple() && !IsAnnotatedParallel)) {
+ emitAnalysis(VectorizationReport(Ld)
+ << "read with atomic ordering or volatile read");
+ DEBUG(dbgs() << "LV: Found a non-simple load.\n");
+ return false;
+ }
+ 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(VectorizationReport(it) <<
+ "instruction cannot be vectorized");
+ return false;
+ }
+ if (!St->isSimple() && !IsAnnotatedParallel) {
+ emitAnalysis(VectorizationReport(St)
+ << "write with atomic ordering or volatile write");
+ DEBUG(dbgs() << "LV: Found a non-simple store.\n");
+ return false;
+ }
+ 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() << "LV: Found a read-only loop!\n");
+ return true;
+ }
+
+ AccessAnalysis::DepCandidates DependentAccesses;
+ AccessAnalysis Accesses(DL, AA, 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();
+
+ if (isUniform(Ptr)) {
+ emitAnalysis(
+ VectorizationReport(ST)
+ << "write to a loop invariant address could not be vectorized");
+ DEBUG(dbgs() << "LV: We don't allow storing to uniform addresses\n");
+ return false;
+ }
+
+ // 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()))
+ Loc.AATags.TBAA = nullptr;
+
+ Accesses.addStore(Loc);
+ }
+ }
+
+ if (IsAnnotatedParallel) {
+ DEBUG(dbgs()
+ << "LV: A loop annotated parallel, ignore memory dependency "
+ << "checks.\n");
+ return true;
+ }
+
+ 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, DL, 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()))
+ 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() << "LV: Found a write-only loop!\n");
+ return true;
+ }
+
+ // 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.
+ unsigned NumComparisons = 0;
+ bool CanDoRT = false;
+ if (NeedRTCheck)
+ CanDoRT = Accesses.canCheckPtrAtRT(PtrRtCheck, NumComparisons, SE, TheLoop,
+ Strides);
+
+ DEBUG(dbgs() << "LV: 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 did not collect too many pointers or found an unsizeable
+ // pointer.
+ if (!CanDoRT || NumComparisons > VectParams.RuntimeMemoryCheckThreshold) {
+ PtrRtCheck.reset();
+ CanDoRT = false;
+ }
+
+ if (CanDoRT) {
+ DEBUG(dbgs() << "LV: We can perform a memory runtime check if needed.\n");
+ }
+
+ if (NeedRTCheck && !CanDoRT) {
+ emitAnalysis(VectorizationReport() << "cannot identify array bounds");
+ DEBUG(dbgs() << "LV: We can't vectorize because we can't find " <<
+ "the array bounds.\n");
+ PtrRtCheck.reset();
+ return false;
+ }
+
+ PtrRtCheck.Need = NeedRTCheck;
+
+ bool CanVecMem = true;
+ if (Accesses.isDependencyCheckNeeded()) {
+ DEBUG(dbgs() << "LV: Checking memory dependencies\n");
+ CanVecMem = DepChecker.areDepsSafe(
+ DependentAccesses, Accesses.getDependenciesToCheck(), Strides);
+ MaxSafeDepDistBytes = DepChecker.getMaxSafeDepDistBytes();
+
+ if (!CanVecMem && DepChecker.shouldRetryWithRuntimeCheck()) {
+ DEBUG(dbgs() << "LV: 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 did not collect too many pointers or found an unsizeable
+ // pointer.
+ if (!CanDoRT || NumComparisons > VectParams.RuntimeMemoryCheckThreshold) {
+ if (!CanDoRT && NumComparisons > 0)
+ emitAnalysis(VectorizationReport()
+ << "cannot check memory dependencies at runtime");
+ else
+ emitAnalysis(VectorizationReport()
+ << NumComparisons << " exceeds limit of "
+ << VectParams.RuntimeMemoryCheckThreshold
+ << " dependent memory operations checked at runtime");
+ DEBUG(dbgs() << "LV: Can't vectorize with memory checks\n");
+ PtrRtCheck.reset();
+ return false;
+ }
+
+ CanVecMem = true;
+ }
+ }
+
+ if (!CanVecMem)
+ emitAnalysis(VectorizationReport() <<
+ "unsafe dependent memory operations in loop");
+
+ DEBUG(dbgs() << "LV: We" << (NeedRTCheck ? "" : " don't") <<
+ " need a runtime memory check.\n");
+
+ return CanVecMem;
+}
+
+bool LoopAccessAnalysis::blockNeedsPredication(BasicBlock *BB) {
+ 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 LoopAccessAnalysis::emitAnalysis(VectorizationReport &Message) {
+ VectorizationReport::emitAnalysis(Message, TheFunction, TheLoop);
+}
+
+bool LoopAccessAnalysis::isUniform(Value *V) {
+ return (SE->isLoopInvariant(SE->getSCEV(V), TheLoop));
+}
Modified: llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp?rev=227756&r1=227755&r2=227756&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp (original)
+++ llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp Sun Feb 1 10:56:15 2015
@@ -58,6 +58,7 @@
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/Analysis/CodeMetrics.h"
+#include "llvm/Analysis/LoopAccessAnalysis.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopIterator.h"
#include "llvm/Analysis/LoopPass.h"
@@ -218,35 +219,6 @@ class LoopVectorizationLegality;
class LoopVectorizationCostModel;
class LoopVectorizeHints;
-/// Optimization analysis message produced during vectorization. Messages inform
-/// the user why vectorization did not occur.
-class VectorizationReport {
- std::string Message;
- raw_string_ostream Out;
- Instruction *Instr;
-
-public:
- VectorizationReport(Instruction *I = nullptr) : Out(Message), Instr(I) {
- Out << "loop not vectorized: ";
- }
-
- template <typename A> VectorizationReport &operator<<(const A &Value) {
- Out << Value;
- return *this;
- }
-
- Instruction *getInstr() { return Instr; }
-
- std::string &str() { return Out.str(); }
- operator Twine() { return Out.str(); }
-
- /// \brief Emit an analysis note with the debug location from the instruction
- /// in \p Message if available. Otherwise use the location of \p TheLoop.
- static void emitAnalysis(VectorizationReport &Message,
- const Function *TheFunction,
- const Loop *TheLoop);
-};
-
/// InnerLoopVectorizer vectorizes loops which contain only one basic
/// block to a specified vectorization factor (VF).
/// This class performs the widening of scalars into vectors, or multiple
@@ -557,16 +529,6 @@ static void propagateMetadata(Instructio
}
}
-void VectorizationReport::emitAnalysis(VectorizationReport &Message,
- const Function *TheFunction,
- const Loop *TheLoop) {
- DebugLoc DL = TheLoop->getStartLoc();
- if (Instruction *I = Message.getInstr())
- DL = I->getDebugLoc();
- emitOptimizationRemarkAnalysis(TheFunction->getContext(), DEBUG_TYPE,
- *TheFunction, DL, Message.str());
-}
-
/// \brief Propagate known metadata from one instruction to a vector of others.
static void propagateMetadata(SmallVectorImpl<Value *> &To, const Instruction *From) {
for (Value *V : To)
@@ -574,133 +536,6 @@ static void propagateMetadata(SmallVecto
propagateMetadata(I, From);
}
-namespace {
-/// \brief Drive the analysis of memory accesses in the loop
-///
-/// This class is responsible for analyzing the memory accesses of a loop. It
-/// collects the accesses and then its main helper the AccessAnalysis class
-/// finds and categorizes the dependences in buildDependenceSets.
-///
-/// For memory dependences that can be analyzed at compile time, it determines
-/// whether the dependence is part of cycle inhibiting vectorization. This work
-/// is delegated to the MemoryDepChecker class.
-///
-/// For memory dependences that cannot be determined at compile time, it
-/// generates run-time checks to prove independence. This is done by
-/// AccessAnalysis::canCheckPtrAtRT and the checks are maintained by the
-/// RuntimePointerCheck class.
-class LoopAccessAnalysis {
-public:
- /// \brief Collection of parameters used from the vectorizer.
- struct VectorizerParams {
- /// \brief Maximum simd width.
- unsigned MaxVectorWidth;
-
- /// \brief VF as overridden by the user.
- unsigned VectorizationFactor;
- /// \brief Interleave factor as overridden by the user.
- unsigned VectorizationInterleave;
-
- /// \\brief When performing memory disambiguation checks at runtime do not
- /// make more than this number of comparisons.
- unsigned RuntimeMemoryCheckThreshold;
-
- VectorizerParams(unsigned MaxVectorWidth,
- unsigned VectorizationFactor,
- unsigned VectorizationInterleave,
- unsigned RuntimeMemoryCheckThreshold) :
- MaxVectorWidth(MaxVectorWidth),
- VectorizationFactor(VectorizationFactor),
- VectorizationInterleave(VectorizationInterleave),
- RuntimeMemoryCheckThreshold(RuntimeMemoryCheckThreshold) {}
- };
-
- /// This struct holds information about the memory runtime legality check that
- /// a group of pointers do not overlap.
- struct RuntimePointerCheck {
- RuntimePointerCheck() : Need(false) {}
-
- /// Reset the state of the pointer runtime information.
- void reset() {
- Need = false;
- Pointers.clear();
- Starts.clear();
- Ends.clear();
- IsWritePtr.clear();
- DependencySetId.clear();
- AliasSetId.clear();
- }
-
- /// Insert a pointer and calculate the start and end SCEVs.
- void insert(ScalarEvolution *SE, Loop *Lp, Value *Ptr, bool WritePtr,
- unsigned DepSetId, unsigned ASId, ValueToValueMap &Strides);
-
- /// This flag indicates if we need to add the runtime check.
- bool Need;
- /// Holds the pointers that we need to check.
- SmallVector<TrackingVH<Value>, 2> Pointers;
- /// Holds the pointer value at the beginning of the loop.
- SmallVector<const SCEV*, 2> Starts;
- /// Holds the pointer value at the end of the loop.
- SmallVector<const SCEV*, 2> Ends;
- /// Holds the information if this pointer is used for writing to memory.
- SmallVector<bool, 2> IsWritePtr;
- /// Holds the id of the set of pointers that could be dependent because of a
- /// shared underlying object.
- SmallVector<unsigned, 2> DependencySetId;
- /// Holds the id of the disjoint alias set to which this pointer belongs.
- SmallVector<unsigned, 2> AliasSetId;
- };
-
- LoopAccessAnalysis(Function *F, Loop *L, ScalarEvolution *SE,
- const DataLayout *DL, const TargetLibraryInfo *TLI,
- AliasAnalysis *AA, DominatorTree *DT,
- const VectorizerParams &VectParams) :
- TheFunction(F), TheLoop(L), SE(SE), DL(DL), TLI(TLI), AA(AA), DT(DT),
- NumLoads(0), NumStores(0), MaxSafeDepDistBytes(-1U),
- VectParams(VectParams) {}
-
- /// Return true we can analyze the memory accesses in the loop and there are
- /// no memory dependence cycles. Replaces symbolic strides using Strides.
- bool canVectorizeMemory(ValueToValueMap &Strides);
-
- RuntimePointerCheck *getRuntimePointerCheck() { return &PtrRtCheck; }
-
- /// Return true if the block BB needs to be predicated in order for the loop
- /// to be vectorized.
- bool blockNeedsPredication(BasicBlock *BB);
-
- /// Returns true if the value V is uniform within the loop.
- bool isUniform(Value *V);
-
- unsigned getMaxSafeDepDistBytes() { return MaxSafeDepDistBytes; }
-
-private:
- void emitAnalysis(Report &Message) {
- emitLoopAnalysis(Message, TheFunction, TheLoop);
- }
-
- /// We need to check that all of the pointers in this list are disjoint
- /// at runtime.
- RuntimePointerCheck PtrRtCheck;
- Function *TheFunction;
- Loop *TheLoop;
- ScalarEvolution *SE;
- const DataLayout *DL;
- const TargetLibraryInfo *TLI;
- AliasAnalysis *AA;
- DominatorTree *DT;
-
- unsigned NumLoads;
- unsigned NumStores;
-
- unsigned MaxSafeDepDistBytes;
-
- /// \brief Vectorizer parameters used by the analysis.
- VectorizerParams VectParams;
-};
-} // end anonymous namespace
-
/// LoopVectorizationLegality checks if it is legal to vectorize a loop, and
/// to what vectorization factor.
/// This class does not look at the profitability of vectorization, only the
@@ -1670,68 +1505,6 @@ struct LoopVectorize : public FunctionPa
// LoopVectorizationCostModel.
//===----------------------------------------------------------------------===//
-static Value *stripIntegerCast(Value *V) {
- if (CastInst *CI = dyn_cast<CastInst>(V))
- if (CI->getOperand(0)->getType()->isIntegerTy())
- return CI->getOperand(0);
- return V;
-}
-
-///\brief Replaces the symbolic stride in a pointer SCEV expression by one.
-///
-/// If \p OrigPtr is not null, use it to look up the stride value instead of
-/// \p Ptr.
-static const SCEV *replaceSymbolicStrideSCEV(ScalarEvolution *SE,
- ValueToValueMap &PtrToStride,
- Value *Ptr, Value *OrigPtr = nullptr) {
-
- 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::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() << "LV: Replacing SCEV: " << *OrigSCEV << " by: " << *ByOne
- << "\n");
- return ByOne;
- }
-
- // Otherwise, just return the SCEV of the original pointer.
- return SE->getSCEV(Ptr);
-}
-
-void LoopAccessAnalysis::RuntimePointerCheck::insert(ScalarEvolution *SE,
- Loop *Lp, Value *Ptr,
- bool WritePtr,
- unsigned DepSetId,
- unsigned ASId,
- 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);
-}
-
Value *InnerLoopVectorizer::getBroadcastInstrs(Value *V) {
// We need to place the broadcast of invariant variables outside the loop.
Instruction *Instr = dyn_cast<Instruction>(V);
@@ -1888,10 +1661,6 @@ int LoopVectorizationLegality::isConsecu
return 0;
}
-bool LoopAccessAnalysis::isUniform(Value *V) {
- return (SE->isLoopInvariant(SE->getSCEV(V), TheLoop));
-}
-
bool LoopVectorizationLegality::isUniform(Value *V) {
return LAA.isUniform(V);
}
@@ -4154,982 +3923,6 @@ void LoopVectorizationLegality::collectL
}
}
-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;
-
- /// \brief Set of potential dependent memory accesses.
- typedef EquivalenceClasses<MemAccessInfo> DepCandidates;
-
- AccessAnalysis(const DataLayout *Dl, AliasAnalysis *AA, DepCandidates &DA) :
- DL(Dl), AST(*AA), 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(LoopAccessAnalysis::RuntimePointerCheck &RtCheck,
- unsigned &NumComparisons,
- ScalarEvolution *SE, Loop *TheLoop,
- 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;
-
- /// Set of accesses that need a further dependence check.
- MemAccessInfoSet CheckDeps;
-
- /// Set of pointers that are read only.
- SmallPtrSet<Value*, 16> ReadOnlyPtr;
-
- const DataLayout *DL;
-
- /// An alias set tracker to partition the access set by underlying object and
- //intrinsic property (such as TBAA metadata).
- AliasSetTracker AST;
-
- /// Sets of potentially dependent accesses - members of one set share an
- /// underlying pointer. The set "CheckDeps" identfies which sets really need a
- /// dependence check.
- DepCandidates &DepCands;
-
- bool IsRTCheckNeeded;
-};
-
-} // end anonymous namespace
-
-/// \brief Check whether a pointer can participate in a runtime bounds check.
-static bool hasComputableBounds(ScalarEvolution *SE, 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, const DataLayout *DL, Value *Ptr,
- const Loop *Lp, ValueToValueMap &StridesMap);
-
-bool AccessAnalysis::canCheckPtrAtRT(
- LoopAccessAnalysis::RuntimePointerCheck &RtCheck,
- unsigned &NumComparisons, ScalarEvolution *SE, Loop *TheLoop,
- 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, DL, 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() << "LV: 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() << "LV: 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() << "LV: Processing memory accesses...\n");
- DEBUG(dbgs() << " AST: "; AST.dump());
- DEBUG(dbgs() << "LV: Accesses:\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);
- for (Value *UnderlyingObj : TempObjects) {
- UnderlyingObjToAccessMap::iterator Prev =
- ObjToLastAccess.find(UnderlyingObj);
- if (Prev != ObjToLastAccess.end())
- DepCands.unionSets(Access, Prev->second);
-
- ObjToLastAccess[UnderlyingObj] = Access;
- }
- }
- }
- }
- }
-}
-
-namespace {
-/// \brief Checks memory dependences among accesses to the same underlying
-/// object to determine whether there vectorization is legal or not (and at
-/// which vectorization factor).
-///
-/// This class works under the assumption that we already checked that memory
-/// locations with different underlying pointers are "must-not alias".
-/// We use the ScalarEvolution framework to symbolically evalutate access
-/// functions pairs. Since we currently don't restructure the loop we can rely
-/// on the program order of memory accesses to determine their safety.
-/// At the moment we will only deem accesses as safe for:
-/// * A negative constant distance assuming program order.
-///
-/// Safe: tmp = a[i + 1]; OR a[i + 1] = x;
-/// a[i] = tmp; y = a[i];
-///
-/// The latter case is safe because later checks guarantuee that there can't
-/// be a cycle through a phi node (that is, we check that "x" and "y" is not
-/// the same variable: a header phi can only be an induction or a reduction, a
-/// reduction can't have a memory sink, an induction can't have a memory
-/// source). This is important and must not be violated (or we have to
-/// resort to checking for cycles through memory).
-///
-/// * A positive constant distance assuming program order that is bigger
-/// than the biggest memory access.
-///
-/// tmp = a[i] OR b[i] = x
-/// a[i+2] = tmp y = b[i+2];
-///
-/// Safe distance: 2 x sizeof(a[0]), and 2 x sizeof(b[0]), respectively.
-///
-/// * Zero distances and all accesses have the same size.
-///
-class MemoryDepChecker {
-public:
- typedef PointerIntPair<Value *, 1, bool> MemAccessInfo;
- typedef SmallPtrSet<MemAccessInfo, 8> MemAccessInfoSet;
-
- MemoryDepChecker(ScalarEvolution *Se, const DataLayout *Dl, const Loop *L,
- const LoopAccessAnalysis::VectorizerParams &VectParams)
- : SE(Se), DL(Dl), InnermostLoop(L), AccessIdx(0),
- ShouldRetryWithRuntimeCheck(false), VectParams(VectParams) {}
-
- /// \brief Register the location (instructions are given increasing numbers)
- /// of a write access.
- void addAccess(StoreInst *SI) {
- Value *Ptr = SI->getPointerOperand();
- Accesses[MemAccessInfo(Ptr, true)].push_back(AccessIdx);
- InstMap.push_back(SI);
- ++AccessIdx;
- }
-
- /// \brief Register the location (instructions are given increasing numbers)
- /// of a write access.
- void addAccess(LoadInst *LI) {
- Value *Ptr = LI->getPointerOperand();
- Accesses[MemAccessInfo(Ptr, false)].push_back(AccessIdx);
- InstMap.push_back(LI);
- ++AccessIdx;
- }
-
- /// \brief Check whether the dependencies between the accesses are safe.
- ///
- /// Only checks sets with elements in \p CheckDeps.
- bool areDepsSafe(AccessAnalysis::DepCandidates &AccessSets,
- MemAccessInfoSet &CheckDeps, ValueToValueMap &Strides);
-
- /// \brief The maximum number of bytes of a vector register we can vectorize
- /// the accesses safely with.
- unsigned getMaxSafeDepDistBytes() { return MaxSafeDepDistBytes; }
-
- /// \brief In same cases when the dependency check fails we can still
- /// vectorize the loop with a dynamic array access check.
- bool shouldRetryWithRuntimeCheck() { return ShouldRetryWithRuntimeCheck; }
-
-private:
- ScalarEvolution *SE;
- const DataLayout *DL;
- const Loop *InnermostLoop;
-
- /// \brief Maps access locations (ptr, read/write) to program order.
- DenseMap<MemAccessInfo, std::vector<unsigned> > Accesses;
-
- /// \brief Memory access instructions in program order.
- SmallVector<Instruction *, 16> InstMap;
-
- /// \brief The program order index to be used for the next instruction.
- unsigned AccessIdx;
-
- // We can access this many bytes in parallel safely.
- unsigned MaxSafeDepDistBytes;
-
- /// \brief If we see a non-constant dependence distance we can still try to
- /// vectorize this loop with runtime checks.
- bool ShouldRetryWithRuntimeCheck;
-
- /// \brief Vectorizer parameters used by the analysis.
- LoopAccessAnalysis::VectorizerParams VectParams;
-
- /// \brief Check whether there is a plausible dependence between the two
- /// accesses.
- ///
- /// Access \p A must happen before \p B in program order. The two indices
- /// identify the index into the program order map.
- ///
- /// This function checks whether there is a plausible dependence (or the
- /// absence of such can't be proved) between the two accesses. If there is a
- /// plausible dependence but the dependence distance is bigger than one
- /// element access it records this distance in \p MaxSafeDepDistBytes (if this
- /// distance is smaller than any other distance encountered so far).
- /// Otherwise, this function returns true signaling a possible dependence.
- bool isDependent(const MemAccessInfo &A, unsigned AIdx,
- const MemAccessInfo &B, unsigned BIdx,
- ValueToValueMap &Strides);
-
- /// \brief Check whether the data dependence could prevent store-load
- /// forwarding.
- bool couldPreventStoreLoadForward(unsigned Distance, unsigned TypeByteSize);
-};
-
-} // end anonymous namespace
-
-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, const DataLayout *DL, Value *Ptr,
- const Loop *Lp, 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() << "LV: 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() << "LV: 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() << "LV: 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() << "LV: 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() << "LV: Bad stride - Not a constant strided " << *Ptr <<
- " SCEV: " << *PtrScev << "\n");
- return 0;
- }
-
- 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::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 = VectParams.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() << "LV: Distance " << Distance <<
- " that could cause a store-load forwarding conflict\n");
- return true;
- }
-
- if (MaxVFWithoutSLForwardIssues < MaxSafeDepDistBytes &&
- MaxVFWithoutSLForwardIssues != VectParams.MaxVectorWidth*TypeByteSize)
- MaxSafeDepDistBytes = MaxVFWithoutSLForwardIssues;
- return false;
-}
-
-bool MemoryDepChecker::isDependent(const MemAccessInfo &A, unsigned AIdx,
- const MemAccessInfo &B, unsigned BIdx,
- 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 false;
-
- // We cannot check pointers in different address spaces.
- if (APtr->getType()->getPointerAddressSpace() !=
- BPtr->getType()->getPointerAddressSpace())
- return true;
-
- const SCEV *AScev = replaceSymbolicStrideSCEV(SE, Strides, APtr);
- const SCEV *BScev = replaceSymbolicStrideSCEV(SE, Strides, BPtr);
-
- int StrideAPtr = isStridedPtr(SE, DL, APtr, InnermostLoop, Strides);
- int StrideBPtr = isStridedPtr(SE, DL, 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() << "LV: Src Scev: " << *Src << "Sink Scev: " << *Sink
- << "(Induction step: " << StrideAPtr << ")\n");
- DEBUG(dbgs() << "LV: 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 true;
- }
-
- const SCEVConstant *C = dyn_cast<SCEVConstant>(Dist);
- if (!C) {
- DEBUG(dbgs() << "LV: Dependence because of non-constant distance\n");
- ShouldRetryWithRuntimeCheck = true;
- return true;
- }
-
- Type *ATy = APtr->getType()->getPointerElementType();
- Type *BTy = BPtr->getType()->getPointerElementType();
- 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 true;
-
- DEBUG(dbgs() << "LV: Dependence is negative: NoDep\n");
- return false;
- }
-
- // 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 false;
- DEBUG(dbgs() << "LV: Zero dependence difference but different types\n");
- return true;
- }
-
- assert(Val.isStrictlyPositive() && "Expect a positive value");
-
- // Positive distance bigger than max vectorization factor.
- if (ATy != BTy) {
- DEBUG(dbgs() <<
- "LV: ReadWrite-Write positive dependency with different types\n");
- return false;
- }
-
- unsigned Distance = (unsigned) Val.getZExtValue();
-
- // Bail out early if passed-in parameters make vectorization not feasible.
- unsigned ForcedFactor = (VectParams.VectorizationFactor ?
- VectParams.VectorizationFactor : 1);
- unsigned ForcedUnroll = (VectParams.VectorizationInterleave ?
- VectParams.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() << "LV: Failure because of Positive distance "
- << Val.getSExtValue() << '\n');
- return true;
- }
-
- MaxSafeDepDistBytes = Distance < MaxSafeDepDistBytes ?
- Distance : MaxSafeDepDistBytes;
-
- bool IsTrueDataDependence = (!AIsWrite && BIsWrite);
- if (IsTrueDataDependence &&
- couldPreventStoreLoadForward(Distance, TypeByteSize))
- return true;
-
- DEBUG(dbgs() << "LV: Positive distance " << Val.getSExtValue() <<
- " with max VF = " << MaxSafeDepDistBytes / TypeByteSize << '\n');
-
- return false;
-}
-
-bool MemoryDepChecker::areDepsSafe(AccessAnalysis::DepCandidates &AccessSets,
- MemAccessInfoSet &CheckDeps,
- 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) {
- if (*I1 < *I2 && isDependent(*AI, *I1, *OI, *I2, Strides))
- return false;
- if (*I2 < *I1 && isDependent(*OI, *I2, *AI, *I1, Strides))
- return false;
- }
- ++OI;
- }
- AI++;
- }
- }
- return true;
-}
-
-bool LoopAccessAnalysis::canVectorizeMemory(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();
- MemoryDepChecker DepChecker(SE, DL, TheLoop, VectParams);
-
- // 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;
-
- LoadInst *Ld = dyn_cast<LoadInst>(it);
- if (!Ld || (!Ld->isSimple() && !IsAnnotatedParallel)) {
- emitAnalysis(VectorizationReport(Ld)
- << "read with atomic ordering or volatile read");
- DEBUG(dbgs() << "LV: Found a non-simple load.\n");
- return false;
- }
- 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(VectorizationReport(it) <<
- "instruction cannot be vectorized");
- return false;
- }
- if (!St->isSimple() && !IsAnnotatedParallel) {
- emitAnalysis(VectorizationReport(St)
- << "write with atomic ordering or volatile write");
- DEBUG(dbgs() << "LV: Found a non-simple store.\n");
- return false;
- }
- 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() << "LV: Found a read-only loop!\n");
- return true;
- }
-
- AccessAnalysis::DepCandidates DependentAccesses;
- AccessAnalysis Accesses(DL, AA, 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();
-
- if (isUniform(Ptr)) {
- emitAnalysis(
- VectorizationReport(ST)
- << "write to a loop invariant address could not be vectorized");
- DEBUG(dbgs() << "LV: We don't allow storing to uniform addresses\n");
- return false;
- }
-
- // 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()))
- Loc.AATags.TBAA = nullptr;
-
- Accesses.addStore(Loc);
- }
- }
-
- if (IsAnnotatedParallel) {
- DEBUG(dbgs()
- << "LV: A loop annotated parallel, ignore memory dependency "
- << "checks.\n");
- return true;
- }
-
- 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, DL, 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()))
- 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() << "LV: Found a write-only loop!\n");
- return true;
- }
-
- // 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.
- unsigned NumComparisons = 0;
- bool CanDoRT = false;
- if (NeedRTCheck)
- CanDoRT = Accesses.canCheckPtrAtRT(PtrRtCheck, NumComparisons, SE, TheLoop,
- Strides);
-
- DEBUG(dbgs() << "LV: 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 did not collect too many pointers or found an unsizeable
- // pointer.
- if (!CanDoRT || NumComparisons > VectParams.RuntimeMemoryCheckThreshold) {
- PtrRtCheck.reset();
- CanDoRT = false;
- }
-
- if (CanDoRT) {
- DEBUG(dbgs() << "LV: We can perform a memory runtime check if needed.\n");
- }
-
- if (NeedRTCheck && !CanDoRT) {
- emitAnalysis(VectorizationReport() << "cannot identify array bounds");
- DEBUG(dbgs() << "LV: We can't vectorize because we can't find " <<
- "the array bounds.\n");
- PtrRtCheck.reset();
- return false;
- }
-
- PtrRtCheck.Need = NeedRTCheck;
-
- bool CanVecMem = true;
- if (Accesses.isDependencyCheckNeeded()) {
- DEBUG(dbgs() << "LV: Checking memory dependencies\n");
- CanVecMem = DepChecker.areDepsSafe(
- DependentAccesses, Accesses.getDependenciesToCheck(), Strides);
- MaxSafeDepDistBytes = DepChecker.getMaxSafeDepDistBytes();
-
- if (!CanVecMem && DepChecker.shouldRetryWithRuntimeCheck()) {
- DEBUG(dbgs() << "LV: 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 did not collect too many pointers or found an unsizeable
- // pointer.
- if (!CanDoRT || NumComparisons > VectParams.RuntimeMemoryCheckThreshold) {
- if (!CanDoRT && NumComparisons > 0)
- emitAnalysis(VectorizationReport()
- << "cannot check memory dependencies at runtime");
- else
- emitAnalysis(VectorizationReport()
- << NumComparisons << " exceeds limit of "
- << VectParams.RuntimeMemoryCheckThreshold
- << " dependent memory operations checked at runtime");
- DEBUG(dbgs() << "LV: Can't vectorize with memory checks\n");
- PtrRtCheck.reset();
- return false;
- }
-
- CanVecMem = true;
- }
- }
-
- if (!CanVecMem)
- emitAnalysis(VectorizationReport() <<
- "unsafe dependent memory operations in loop");
-
- DEBUG(dbgs() << "LV: We" << (NeedRTCheck ? "" : " don't") <<
- " need a runtime memory check.\n");
-
- return CanVecMem;
-}
-
bool LoopVectorizationLegality::canVectorizeMemory() {
return LAA.canVectorizeMemory(Strides);
}
@@ -5474,14 +4267,6 @@ bool LoopVectorizationLegality::isInduct
return Inductions.count(PN);
}
-bool LoopAccessAnalysis::blockNeedsPredication(BasicBlock *BB) {
- 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);
-}
-
bool LoopVectorizationLegality::blockNeedsPredication(BasicBlock *BB) {
return LAA.blockNeedsPredication(BB);
}
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