1862 lines
69 KiB
C++
1862 lines
69 KiB
C++
//===- LoopAccessAnalysis.cpp - Loop Access Analysis Implementation --------==//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// The implementation for the loop memory dependence that was originally
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// developed for the loop vectorizer.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/LoopAccessAnalysis.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/ScalarEvolutionExpander.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/DiagnosticInfo.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Analysis/VectorUtils.h"
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using namespace llvm;
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#define DEBUG_TYPE "loop-accesses"
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static cl::opt<unsigned, true>
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VectorizationFactor("force-vector-width", cl::Hidden,
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cl::desc("Sets the SIMD width. Zero is autoselect."),
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cl::location(VectorizerParams::VectorizationFactor));
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unsigned VectorizerParams::VectorizationFactor;
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static cl::opt<unsigned, true>
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VectorizationInterleave("force-vector-interleave", cl::Hidden,
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cl::desc("Sets the vectorization interleave count. "
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"Zero is autoselect."),
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cl::location(
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VectorizerParams::VectorizationInterleave));
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unsigned VectorizerParams::VectorizationInterleave;
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static cl::opt<unsigned, true> RuntimeMemoryCheckThreshold(
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"runtime-memory-check-threshold", cl::Hidden,
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cl::desc("When performing memory disambiguation checks at runtime do not "
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"generate more than this number of comparisons (default = 8)."),
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cl::location(VectorizerParams::RuntimeMemoryCheckThreshold), cl::init(8));
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unsigned VectorizerParams::RuntimeMemoryCheckThreshold;
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/// \brief The maximum iterations used to merge memory checks
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static cl::opt<unsigned> MemoryCheckMergeThreshold(
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"memory-check-merge-threshold", cl::Hidden,
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cl::desc("Maximum number of comparisons done when trying to merge "
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"runtime memory checks. (default = 100)"),
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cl::init(100));
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/// Maximum SIMD width.
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const unsigned VectorizerParams::MaxVectorWidth = 64;
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/// \brief We collect dependences up to this threshold.
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static cl::opt<unsigned>
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MaxDependences("max-dependences", cl::Hidden,
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cl::desc("Maximum number of dependences collected by "
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"loop-access analysis (default = 100)"),
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cl::init(100));
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bool VectorizerParams::isInterleaveForced() {
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return ::VectorizationInterleave.getNumOccurrences() > 0;
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}
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void LoopAccessReport::emitAnalysis(const LoopAccessReport &Message,
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const Function *TheFunction,
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const Loop *TheLoop,
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const char *PassName) {
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DebugLoc DL = TheLoop->getStartLoc();
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if (const Instruction *I = Message.getInstr())
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DL = I->getDebugLoc();
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emitOptimizationRemarkAnalysis(TheFunction->getContext(), PassName,
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*TheFunction, DL, Message.str());
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}
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Value *llvm::stripIntegerCast(Value *V) {
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if (CastInst *CI = dyn_cast<CastInst>(V))
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if (CI->getOperand(0)->getType()->isIntegerTy())
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return CI->getOperand(0);
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return V;
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}
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const SCEV *llvm::replaceSymbolicStrideSCEV(PredicatedScalarEvolution &PSE,
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const ValueToValueMap &PtrToStride,
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Value *Ptr, Value *OrigPtr) {
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const SCEV *OrigSCEV = PSE.getSCEV(Ptr);
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// If there is an entry in the map return the SCEV of the pointer with the
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// symbolic stride replaced by one.
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ValueToValueMap::const_iterator SI =
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PtrToStride.find(OrigPtr ? OrigPtr : Ptr);
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if (SI != PtrToStride.end()) {
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Value *StrideVal = SI->second;
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// Strip casts.
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StrideVal = stripIntegerCast(StrideVal);
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// Replace symbolic stride by one.
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Value *One = ConstantInt::get(StrideVal->getType(), 1);
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ValueToValueMap RewriteMap;
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RewriteMap[StrideVal] = One;
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ScalarEvolution *SE = PSE.getSE();
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const auto *U = cast<SCEVUnknown>(SE->getSCEV(StrideVal));
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const auto *CT =
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static_cast<const SCEVConstant *>(SE->getOne(StrideVal->getType()));
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PSE.addPredicate(*SE->getEqualPredicate(U, CT));
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auto *Expr = PSE.getSCEV(Ptr);
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DEBUG(dbgs() << "LAA: Replacing SCEV: " << *OrigSCEV << " by: " << *Expr
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<< "\n");
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return Expr;
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}
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// Otherwise, just return the SCEV of the original pointer.
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return OrigSCEV;
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}
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void RuntimePointerChecking::insert(Loop *Lp, Value *Ptr, bool WritePtr,
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unsigned DepSetId, unsigned ASId,
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const ValueToValueMap &Strides,
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PredicatedScalarEvolution &PSE) {
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// Get the stride replaced scev.
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const SCEV *Sc = replaceSymbolicStrideSCEV(PSE, Strides, Ptr);
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const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(Sc);
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assert(AR && "Invalid addrec expression");
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ScalarEvolution *SE = PSE.getSE();
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const SCEV *Ex = SE->getBackedgeTakenCount(Lp);
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const SCEV *ScStart = AR->getStart();
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const SCEV *ScEnd = AR->evaluateAtIteration(Ex, *SE);
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const SCEV *Step = AR->getStepRecurrence(*SE);
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// For expressions with negative step, the upper bound is ScStart and the
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// lower bound is ScEnd.
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if (const SCEVConstant *CStep = dyn_cast<const SCEVConstant>(Step)) {
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if (CStep->getValue()->isNegative())
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std::swap(ScStart, ScEnd);
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} else {
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// Fallback case: the step is not constant, but the we can still
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// get the upper and lower bounds of the interval by using min/max
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// expressions.
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ScStart = SE->getUMinExpr(ScStart, ScEnd);
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ScEnd = SE->getUMaxExpr(AR->getStart(), ScEnd);
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}
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Pointers.emplace_back(Ptr, ScStart, ScEnd, WritePtr, DepSetId, ASId, Sc);
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}
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SmallVector<RuntimePointerChecking::PointerCheck, 4>
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RuntimePointerChecking::generateChecks() const {
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SmallVector<PointerCheck, 4> Checks;
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for (unsigned I = 0; I < CheckingGroups.size(); ++I) {
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for (unsigned J = I + 1; J < CheckingGroups.size(); ++J) {
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const RuntimePointerChecking::CheckingPtrGroup &CGI = CheckingGroups[I];
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const RuntimePointerChecking::CheckingPtrGroup &CGJ = CheckingGroups[J];
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if (needsChecking(CGI, CGJ))
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Checks.push_back(std::make_pair(&CGI, &CGJ));
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}
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}
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return Checks;
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}
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void RuntimePointerChecking::generateChecks(
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MemoryDepChecker::DepCandidates &DepCands, bool UseDependencies) {
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assert(Checks.empty() && "Checks is not empty");
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groupChecks(DepCands, UseDependencies);
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Checks = generateChecks();
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}
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bool RuntimePointerChecking::needsChecking(const CheckingPtrGroup &M,
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const CheckingPtrGroup &N) const {
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for (unsigned I = 0, EI = M.Members.size(); EI != I; ++I)
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for (unsigned J = 0, EJ = N.Members.size(); EJ != J; ++J)
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if (needsChecking(M.Members[I], N.Members[J]))
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return true;
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return false;
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}
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/// Compare \p I and \p J and return the minimum.
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/// Return nullptr in case we couldn't find an answer.
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static const SCEV *getMinFromExprs(const SCEV *I, const SCEV *J,
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ScalarEvolution *SE) {
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const SCEV *Diff = SE->getMinusSCEV(J, I);
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const SCEVConstant *C = dyn_cast<const SCEVConstant>(Diff);
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if (!C)
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return nullptr;
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if (C->getValue()->isNegative())
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return J;
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return I;
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}
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bool RuntimePointerChecking::CheckingPtrGroup::addPointer(unsigned Index) {
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const SCEV *Start = RtCheck.Pointers[Index].Start;
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const SCEV *End = RtCheck.Pointers[Index].End;
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// Compare the starts and ends with the known minimum and maximum
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// of this set. We need to know how we compare against the min/max
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// of the set in order to be able to emit memchecks.
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const SCEV *Min0 = getMinFromExprs(Start, Low, RtCheck.SE);
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if (!Min0)
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return false;
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const SCEV *Min1 = getMinFromExprs(End, High, RtCheck.SE);
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if (!Min1)
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return false;
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// Update the low bound expression if we've found a new min value.
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if (Min0 == Start)
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Low = Start;
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// Update the high bound expression if we've found a new max value.
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if (Min1 != End)
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High = End;
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Members.push_back(Index);
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return true;
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}
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void RuntimePointerChecking::groupChecks(
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MemoryDepChecker::DepCandidates &DepCands, bool UseDependencies) {
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// We build the groups from dependency candidates equivalence classes
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// because:
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// - We know that pointers in the same equivalence class share
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// the same underlying object and therefore there is a chance
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// that we can compare pointers
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// - We wouldn't be able to merge two pointers for which we need
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// to emit a memcheck. The classes in DepCands are already
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// conveniently built such that no two pointers in the same
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// class need checking against each other.
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// We use the following (greedy) algorithm to construct the groups
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// For every pointer in the equivalence class:
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// For each existing group:
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// - if the difference between this pointer and the min/max bounds
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// of the group is a constant, then make the pointer part of the
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// group and update the min/max bounds of that group as required.
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CheckingGroups.clear();
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// If we need to check two pointers to the same underlying object
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// with a non-constant difference, we shouldn't perform any pointer
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// grouping with those pointers. This is because we can easily get
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// into cases where the resulting check would return false, even when
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// the accesses are safe.
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//
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// The following example shows this:
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// for (i = 0; i < 1000; ++i)
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// a[5000 + i * m] = a[i] + a[i + 9000]
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//
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// Here grouping gives a check of (5000, 5000 + 1000 * m) against
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// (0, 10000) which is always false. However, if m is 1, there is no
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// dependence. Not grouping the checks for a[i] and a[i + 9000] allows
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// us to perform an accurate check in this case.
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//
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// The above case requires that we have an UnknownDependence between
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// accesses to the same underlying object. This cannot happen unless
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// ShouldRetryWithRuntimeCheck is set, and therefore UseDependencies
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// is also false. In this case we will use the fallback path and create
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// separate checking groups for all pointers.
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// If we don't have the dependency partitions, construct a new
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// checking pointer group for each pointer. This is also required
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// for correctness, because in this case we can have checking between
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// pointers to the same underlying object.
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if (!UseDependencies) {
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for (unsigned I = 0; I < Pointers.size(); ++I)
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CheckingGroups.push_back(CheckingPtrGroup(I, *this));
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return;
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}
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unsigned TotalComparisons = 0;
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DenseMap<Value *, unsigned> PositionMap;
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for (unsigned Index = 0; Index < Pointers.size(); ++Index)
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PositionMap[Pointers[Index].PointerValue] = Index;
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// We need to keep track of what pointers we've already seen so we
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// don't process them twice.
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SmallSet<unsigned, 2> Seen;
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// Go through all equivalence classes, get the "pointer check groups"
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// and add them to the overall solution. We use the order in which accesses
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// appear in 'Pointers' to enforce determinism.
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for (unsigned I = 0; I < Pointers.size(); ++I) {
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// We've seen this pointer before, and therefore already processed
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// its equivalence class.
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if (Seen.count(I))
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continue;
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MemoryDepChecker::MemAccessInfo Access(Pointers[I].PointerValue,
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Pointers[I].IsWritePtr);
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SmallVector<CheckingPtrGroup, 2> Groups;
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auto LeaderI = DepCands.findValue(DepCands.getLeaderValue(Access));
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// Because DepCands is constructed by visiting accesses in the order in
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// which they appear in alias sets (which is deterministic) and the
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// iteration order within an equivalence class member is only dependent on
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// the order in which unions and insertions are performed on the
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// equivalence class, the iteration order is deterministic.
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for (auto MI = DepCands.member_begin(LeaderI), ME = DepCands.member_end();
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MI != ME; ++MI) {
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unsigned Pointer = PositionMap[MI->getPointer()];
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bool Merged = false;
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// Mark this pointer as seen.
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Seen.insert(Pointer);
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// Go through all the existing sets and see if we can find one
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// which can include this pointer.
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for (CheckingPtrGroup &Group : Groups) {
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// Don't perform more than a certain amount of comparisons.
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// This should limit the cost of grouping the pointers to something
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// reasonable. If we do end up hitting this threshold, the algorithm
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// will create separate groups for all remaining pointers.
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if (TotalComparisons > MemoryCheckMergeThreshold)
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break;
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TotalComparisons++;
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if (Group.addPointer(Pointer)) {
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Merged = true;
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break;
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}
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}
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if (!Merged)
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// We couldn't add this pointer to any existing set or the threshold
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// for the number of comparisons has been reached. Create a new group
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// to hold the current pointer.
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Groups.push_back(CheckingPtrGroup(Pointer, *this));
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}
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// We've computed the grouped checks for this partition.
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// Save the results and continue with the next one.
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std::copy(Groups.begin(), Groups.end(), std::back_inserter(CheckingGroups));
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}
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}
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bool RuntimePointerChecking::arePointersInSamePartition(
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const SmallVectorImpl<int> &PtrToPartition, unsigned PtrIdx1,
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unsigned PtrIdx2) {
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return (PtrToPartition[PtrIdx1] != -1 &&
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PtrToPartition[PtrIdx1] == PtrToPartition[PtrIdx2]);
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}
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bool RuntimePointerChecking::needsChecking(unsigned I, unsigned J) const {
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const PointerInfo &PointerI = Pointers[I];
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const PointerInfo &PointerJ = Pointers[J];
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// No need to check if two readonly pointers intersect.
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if (!PointerI.IsWritePtr && !PointerJ.IsWritePtr)
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return false;
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// Only need to check pointers between two different dependency sets.
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if (PointerI.DependencySetId == PointerJ.DependencySetId)
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return false;
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// Only need to check pointers in the same alias set.
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if (PointerI.AliasSetId != PointerJ.AliasSetId)
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return false;
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return true;
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}
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void RuntimePointerChecking::printChecks(
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raw_ostream &OS, const SmallVectorImpl<PointerCheck> &Checks,
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unsigned Depth) const {
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unsigned N = 0;
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for (const auto &Check : Checks) {
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const auto &First = Check.first->Members, &Second = Check.second->Members;
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OS.indent(Depth) << "Check " << N++ << ":\n";
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OS.indent(Depth + 2) << "Comparing group (" << Check.first << "):\n";
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for (unsigned K = 0; K < First.size(); ++K)
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OS.indent(Depth + 2) << *Pointers[First[K]].PointerValue << "\n";
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OS.indent(Depth + 2) << "Against group (" << Check.second << "):\n";
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for (unsigned K = 0; K < Second.size(); ++K)
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OS.indent(Depth + 2) << *Pointers[Second[K]].PointerValue << "\n";
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}
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}
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void RuntimePointerChecking::print(raw_ostream &OS, unsigned Depth) const {
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OS.indent(Depth) << "Run-time memory checks:\n";
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printChecks(OS, Checks, Depth);
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OS.indent(Depth) << "Grouped accesses:\n";
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for (unsigned I = 0; I < CheckingGroups.size(); ++I) {
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const auto &CG = CheckingGroups[I];
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OS.indent(Depth + 2) << "Group " << &CG << ":\n";
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OS.indent(Depth + 4) << "(Low: " << *CG.Low << " High: " << *CG.High
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<< ")\n";
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for (unsigned J = 0; J < CG.Members.size(); ++J) {
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OS.indent(Depth + 6) << "Member: " << *Pointers[CG.Members[J]].Expr
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<< "\n";
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}
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}
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}
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namespace {
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/// \brief Analyses memory accesses in a loop.
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///
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/// Checks whether run time pointer checks are needed and builds sets for data
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/// dependence checking.
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class AccessAnalysis {
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public:
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/// \brief Read or write access location.
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typedef PointerIntPair<Value *, 1, bool> MemAccessInfo;
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typedef SmallPtrSet<MemAccessInfo, 8> MemAccessInfoSet;
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AccessAnalysis(const DataLayout &Dl, AliasAnalysis *AA, LoopInfo *LI,
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MemoryDepChecker::DepCandidates &DA,
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PredicatedScalarEvolution &PSE)
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: DL(Dl), AST(*AA), LI(LI), DepCands(DA), IsRTCheckAnalysisNeeded(false),
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PSE(PSE) {}
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/// \brief Register a load and whether it is only read from.
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void addLoad(MemoryLocation &Loc, bool IsReadOnly) {
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Value *Ptr = const_cast<Value*>(Loc.Ptr);
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AST.add(Ptr, MemoryLocation::UnknownSize, Loc.AATags);
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Accesses.insert(MemAccessInfo(Ptr, false));
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if (IsReadOnly)
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ReadOnlyPtr.insert(Ptr);
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}
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/// \brief Register a store.
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void addStore(MemoryLocation &Loc) {
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Value *Ptr = const_cast<Value*>(Loc.Ptr);
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AST.add(Ptr, MemoryLocation::UnknownSize, Loc.AATags);
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Accesses.insert(MemAccessInfo(Ptr, true));
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}
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/// \brief Check whether we can check the pointers at runtime for
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/// non-intersection.
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///
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/// Returns true if we need no check or if we do and we can generate them
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/// (i.e. the pointers have computable bounds).
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bool canCheckPtrAtRT(RuntimePointerChecking &RtCheck, ScalarEvolution *SE,
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Loop *TheLoop, const ValueToValueMap &Strides,
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bool ShouldCheckStride = false);
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/// \brief Goes over all memory accesses, checks whether a RT check is needed
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/// and builds sets of dependent accesses.
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void buildDependenceSets() {
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processMemAccesses();
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}
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/// \brief Initial processing of memory accesses determined that we need to
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/// perform dependency checking.
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///
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/// Note that this can later be cleared if we retry memcheck analysis without
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/// dependency checking (i.e. ShouldRetryWithRuntimeCheck).
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bool isDependencyCheckNeeded() { return !CheckDeps.empty(); }
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/// We decided that no dependence analysis would be used. Reset the state.
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void resetDepChecks(MemoryDepChecker &DepChecker) {
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CheckDeps.clear();
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DepChecker.clearDependences();
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}
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MemAccessInfoSet &getDependenciesToCheck() { return CheckDeps; }
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private:
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typedef SetVector<MemAccessInfo> PtrAccessSet;
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|
|
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/// \brief Go over all memory access and check whether runtime pointer checks
|
|
/// are needed and build sets of dependency check candidates.
|
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void processMemAccesses();
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|
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/// Set of all accesses.
|
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PtrAccessSet Accesses;
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|
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const DataLayout &DL;
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|
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/// Set of accesses that need a further dependence check.
|
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MemAccessInfoSet CheckDeps;
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|
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/// Set of pointers that are read only.
|
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SmallPtrSet<Value*, 16> ReadOnlyPtr;
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|
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/// An alias set tracker to partition the access set by underlying object and
|
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//intrinsic property (such as TBAA metadata).
|
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AliasSetTracker AST;
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|
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LoopInfo *LI;
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/// Sets of potentially dependent accesses - members of one set share an
|
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/// underlying pointer. The set "CheckDeps" identfies which sets really need a
|
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/// dependence check.
|
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MemoryDepChecker::DepCandidates &DepCands;
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|
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/// \brief Initial processing of memory accesses determined that we may need
|
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/// to add memchecks. Perform the analysis to determine the necessary checks.
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///
|
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/// Note that, this is different from isDependencyCheckNeeded. When we retry
|
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/// memcheck analysis without dependency checking
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/// (i.e. ShouldRetryWithRuntimeCheck), isDependencyCheckNeeded is cleared
|
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/// while this remains set if we have potentially dependent accesses.
|
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bool IsRTCheckAnalysisNeeded;
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|
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/// The SCEV predicate containing all the SCEV-related assumptions.
|
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PredicatedScalarEvolution &PSE;
|
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};
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|
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} // end anonymous namespace
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/// \brief Check whether a pointer can participate in a runtime bounds check.
|
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static bool hasComputableBounds(PredicatedScalarEvolution &PSE,
|
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const ValueToValueMap &Strides, Value *Ptr,
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Loop *L) {
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const SCEV *PtrScev = replaceSymbolicStrideSCEV(PSE, Strides, Ptr);
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const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev);
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if (!AR)
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return false;
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|
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return AR->isAffine();
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}
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|
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bool AccessAnalysis::canCheckPtrAtRT(RuntimePointerChecking &RtCheck,
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ScalarEvolution *SE, Loop *TheLoop,
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const ValueToValueMap &StridesMap,
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bool ShouldCheckStride) {
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// Find pointers with computable bounds. We are going to use this information
|
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// to place a runtime bound check.
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bool CanDoRT = true;
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bool NeedRTCheck = false;
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if (!IsRTCheckAnalysisNeeded) return true;
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bool IsDepCheckNeeded = isDependencyCheckNeeded();
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// We assign a consecutive id to access from different alias sets.
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// Accesses between different groups doesn't need to be checked.
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unsigned ASId = 1;
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for (auto &AS : AST) {
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int NumReadPtrChecks = 0;
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int NumWritePtrChecks = 0;
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// We assign consecutive id to access from different dependence sets.
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// Accesses within the same set don't need a runtime check.
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unsigned RunningDepId = 1;
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DenseMap<Value *, unsigned> DepSetId;
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for (auto A : AS) {
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Value *Ptr = A.getValue();
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bool IsWrite = Accesses.count(MemAccessInfo(Ptr, true));
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MemAccessInfo Access(Ptr, IsWrite);
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if (IsWrite)
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++NumWritePtrChecks;
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else
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++NumReadPtrChecks;
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if (hasComputableBounds(PSE, StridesMap, Ptr, TheLoop) &&
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// When we run after a failing dependency check we have to make sure
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// we don't have wrapping pointers.
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(!ShouldCheckStride ||
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isStridedPtr(PSE, Ptr, TheLoop, StridesMap) == 1)) {
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// The id of the dependence set.
|
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unsigned DepId;
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|
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if (IsDepCheckNeeded) {
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Value *Leader = DepCands.getLeaderValue(Access).getPointer();
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unsigned &LeaderId = DepSetId[Leader];
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if (!LeaderId)
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LeaderId = RunningDepId++;
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DepId = LeaderId;
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} else
|
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// Each access has its own dependence set.
|
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DepId = RunningDepId++;
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|
|
RtCheck.insert(TheLoop, Ptr, IsWrite, DepId, ASId, StridesMap, PSE);
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|
|
DEBUG(dbgs() << "LAA: Found a runtime check ptr:" << *Ptr << '\n');
|
|
} else {
|
|
DEBUG(dbgs() << "LAA: Can't find bounds for ptr:" << *Ptr << '\n');
|
|
CanDoRT = false;
|
|
}
|
|
}
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|
|
|
// If we have at least two writes or one write and a read then we need to
|
|
// check them. But there is no need to checks if there is only one
|
|
// dependence set for this alias set.
|
|
//
|
|
// Note that this function computes CanDoRT and NeedRTCheck independently.
|
|
// For example CanDoRT=false, NeedRTCheck=false means that we have a pointer
|
|
// for which we couldn't find the bounds but we don't actually need to emit
|
|
// any checks so it does not matter.
|
|
if (!(IsDepCheckNeeded && CanDoRT && RunningDepId == 2))
|
|
NeedRTCheck |= (NumWritePtrChecks >= 2 || (NumReadPtrChecks >= 1 &&
|
|
NumWritePtrChecks >= 1));
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|
|
|
++ASId;
|
|
}
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|
|
|
// 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.Pointers[i].DependencySetId ==
|
|
RtCheck.Pointers[j].DependencySetId)
|
|
continue;
|
|
// Only need to check pointers in the same alias set.
|
|
if (RtCheck.Pointers[i].AliasSetId != RtCheck.Pointers[j].AliasSetId)
|
|
continue;
|
|
|
|
Value *PtrI = RtCheck.Pointers[i].PointerValue;
|
|
Value *PtrJ = RtCheck.Pointers[j].PointerValue;
|
|
|
|
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;
|
|
}
|
|
}
|
|
}
|
|
|
|
if (NeedRTCheck && CanDoRT)
|
|
RtCheck.generateChecks(DepCands, IsDepCheckNeeded);
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|
|
|
DEBUG(dbgs() << "LAA: We need to do " << RtCheck.getNumberOfChecks()
|
|
<< " pointer comparisons.\n");
|
|
|
|
RtCheck.Need = NeedRTCheck;
|
|
|
|
bool CanDoRTIfNeeded = !NeedRTCheck || CanDoRT;
|
|
if (!CanDoRTIfNeeded)
|
|
RtCheck.reset();
|
|
return CanDoRTIfNeeded;
|
|
}
|
|
|
|
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);
|
|
IsRTCheckAnalysisNeeded = 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) {
|
|
// nullptr never alias, don't join sets for pointer that have "null"
|
|
// in their UnderlyingObjects list.
|
|
if (isa<ConstantPointerNull>(UnderlyingObj))
|
|
continue;
|
|
|
|
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 Return true if an AddRec pointer \p Ptr is unsigned non-wrapping,
|
|
/// i.e. monotonically increasing/decreasing.
|
|
static bool isNoWrapAddRec(Value *Ptr, const SCEVAddRecExpr *AR,
|
|
ScalarEvolution *SE, const Loop *L) {
|
|
// FIXME: This should probably only return true for NUW.
|
|
if (AR->getNoWrapFlags(SCEV::NoWrapMask))
|
|
return true;
|
|
|
|
// Scalar evolution does not propagate the non-wrapping flags to values that
|
|
// are derived from a non-wrapping induction variable because non-wrapping
|
|
// could be flow-sensitive.
|
|
//
|
|
// Look through the potentially overflowing instruction to try to prove
|
|
// non-wrapping for the *specific* value of Ptr.
|
|
|
|
// The arithmetic implied by an inbounds GEP can't overflow.
|
|
auto *GEP = dyn_cast<GetElementPtrInst>(Ptr);
|
|
if (!GEP || !GEP->isInBounds())
|
|
return false;
|
|
|
|
// Make sure there is only one non-const index and analyze that.
|
|
Value *NonConstIndex = nullptr;
|
|
for (auto Index = GEP->idx_begin(); Index != GEP->idx_end(); ++Index)
|
|
if (!isa<ConstantInt>(*Index)) {
|
|
if (NonConstIndex)
|
|
return false;
|
|
NonConstIndex = *Index;
|
|
}
|
|
if (!NonConstIndex)
|
|
// The recurrence is on the pointer, ignore for now.
|
|
return false;
|
|
|
|
// The index in GEP is signed. It is non-wrapping if it's derived from a NSW
|
|
// AddRec using a NSW operation.
|
|
if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(NonConstIndex))
|
|
if (OBO->hasNoSignedWrap() &&
|
|
// Assume constant for other the operand so that the AddRec can be
|
|
// easily found.
|
|
isa<ConstantInt>(OBO->getOperand(1))) {
|
|
auto *OpScev = SE->getSCEV(OBO->getOperand(0));
|
|
|
|
if (auto *OpAR = dyn_cast<SCEVAddRecExpr>(OpScev))
|
|
return OpAR->getLoop() == L && OpAR->getNoWrapFlags(SCEV::FlagNSW);
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/// \brief Check whether the access through \p Ptr has a constant stride.
|
|
int llvm::isStridedPtr(PredicatedScalarEvolution &PSE, Value *Ptr,
|
|
const Loop *Lp, const ValueToValueMap &StridesMap) {
|
|
Type *Ty = Ptr->getType();
|
|
assert(Ty->isPointerTy() && "Unexpected non-ptr");
|
|
|
|
// Make sure that the pointer does not point to aggregate types.
|
|
auto *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(PSE, 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 = isNoWrapAddRec(Ptr, AR, PSE.getSE(), Lp);
|
|
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(*PSE.getSE());
|
|
|
|
// Calculate the pointer stride and check if it is constant.
|
|
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->getAPInt();
|
|
|
|
// 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::isBackward() const {
|
|
switch (Type) {
|
|
case NoDep:
|
|
case Forward:
|
|
case ForwardButPreventsForwarding:
|
|
case Unknown:
|
|
return false;
|
|
|
|
case BackwardVectorizable:
|
|
case Backward:
|
|
case BackwardVectorizableButPreventsForwarding:
|
|
return true;
|
|
}
|
|
llvm_unreachable("unexpected DepType!");
|
|
}
|
|
|
|
bool MemoryDepChecker::Dependence::isPossiblyBackward() const {
|
|
return isBackward() || Type == Unknown;
|
|
}
|
|
|
|
bool MemoryDepChecker::Dependence::isForward() const {
|
|
switch (Type) {
|
|
case Forward:
|
|
case ForwardButPreventsForwarding:
|
|
return true;
|
|
|
|
case NoDep:
|
|
case Unknown:
|
|
case BackwardVectorizable:
|
|
case Backward:
|
|
case BackwardVectorizableButPreventsForwarding:
|
|
return false;
|
|
}
|
|
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;
|
|
}
|
|
|
|
/// \brief Check the dependence for two accesses with the same stride \p Stride.
|
|
/// \p Distance is the positive distance and \p TypeByteSize is type size in
|
|
/// bytes.
|
|
///
|
|
/// \returns true if they are independent.
|
|
static bool areStridedAccessesIndependent(unsigned Distance, unsigned Stride,
|
|
unsigned TypeByteSize) {
|
|
assert(Stride > 1 && "The stride must be greater than 1");
|
|
assert(TypeByteSize > 0 && "The type size in byte must be non-zero");
|
|
assert(Distance > 0 && "The distance must be non-zero");
|
|
|
|
// Skip if the distance is not multiple of type byte size.
|
|
if (Distance % TypeByteSize)
|
|
return false;
|
|
|
|
unsigned ScaledDist = Distance / TypeByteSize;
|
|
|
|
// No dependence if the scaled distance is not multiple of the stride.
|
|
// E.g.
|
|
// for (i = 0; i < 1024 ; i += 4)
|
|
// A[i+2] = A[i] + 1;
|
|
//
|
|
// Two accesses in memory (scaled distance is 2, stride is 4):
|
|
// | A[0] | | | | A[4] | | | |
|
|
// | | | A[2] | | | | A[6] | |
|
|
//
|
|
// E.g.
|
|
// for (i = 0; i < 1024 ; i += 3)
|
|
// A[i+4] = A[i] + 1;
|
|
//
|
|
// Two accesses in memory (scaled distance is 4, stride is 3):
|
|
// | A[0] | | | A[3] | | | A[6] | | |
|
|
// | | | | | A[4] | | | A[7] | |
|
|
return ScaledDist % Stride;
|
|
}
|
|
|
|
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(PSE, Strides, APtr);
|
|
const SCEV *BScev = replaceSymbolicStrideSCEV(PSE, Strides, BPtr);
|
|
|
|
int StrideAPtr = isStridedPtr(PSE, APtr, InnermostLoop, Strides);
|
|
int StrideBPtr = isStridedPtr(PSE, 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 = PSE.getSE()->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 accesses with constant stride. 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() << "Pointer access with non-constant stride\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->getAPInt();
|
|
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::Forward;
|
|
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();
|
|
|
|
unsigned Stride = std::abs(StrideAPtr);
|
|
if (Stride > 1 &&
|
|
areStridedAccessesIndependent(Distance, Stride, TypeByteSize)) {
|
|
DEBUG(dbgs() << "LAA: Strided accesses are independent\n");
|
|
return Dependence::NoDep;
|
|
}
|
|
|
|
// 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 minimum number of iterations for a vectorized/unrolled version.
|
|
unsigned MinNumIter = std::max(ForcedFactor * ForcedUnroll, 2U);
|
|
|
|
// It's not vectorizable if the distance is smaller than the minimum distance
|
|
// needed for a vectroized/unrolled version. Vectorizing one iteration in
|
|
// front needs TypeByteSize * Stride. Vectorizing the last iteration needs
|
|
// TypeByteSize (No need to plus the last gap distance).
|
|
//
|
|
// E.g. Assume one char is 1 byte in memory and one int is 4 bytes.
|
|
// foo(int *A) {
|
|
// int *B = (int *)((char *)A + 14);
|
|
// for (i = 0 ; i < 1024 ; i += 2)
|
|
// B[i] = A[i] + 1;
|
|
// }
|
|
//
|
|
// Two accesses in memory (stride is 2):
|
|
// | A[0] | | A[2] | | A[4] | | A[6] | |
|
|
// | B[0] | | B[2] | | B[4] |
|
|
//
|
|
// Distance needs for vectorizing iterations except the last iteration:
|
|
// 4 * 2 * (MinNumIter - 1). Distance needs for the last iteration: 4.
|
|
// So the minimum distance needed is: 4 * 2 * (MinNumIter - 1) + 4.
|
|
//
|
|
// If MinNumIter is 2, it is vectorizable as the minimum distance needed is
|
|
// 12, which is less than distance.
|
|
//
|
|
// If MinNumIter is 4 (Say if a user forces the vectorization factor to be 4),
|
|
// the minimum distance needed is 28, which is greater than distance. It is
|
|
// not safe to do vectorization.
|
|
unsigned MinDistanceNeeded =
|
|
TypeByteSize * Stride * (MinNumIter - 1) + TypeByteSize;
|
|
if (MinDistanceNeeded > Distance) {
|
|
DEBUG(dbgs() << "LAA: Failure because of positive distance " << Distance
|
|
<< '\n');
|
|
return Dependence::Backward;
|
|
}
|
|
|
|
// Unsafe if the minimum distance needed is greater than max safe distance.
|
|
if (MinDistanceNeeded > MaxSafeDepDistBytes) {
|
|
DEBUG(dbgs() << "LAA: Failure because it needs at least "
|
|
<< MinDistanceNeeded << " size in bytes");
|
|
return Dependence::Backward;
|
|
}
|
|
|
|
// Positive distance bigger than max vectorization factor.
|
|
// FIXME: Should use max factor instead of max distance in bytes, which could
|
|
// not handle different types.
|
|
// E.g. Assume one char is 1 byte in memory and one int is 4 bytes.
|
|
// void foo (int *A, char *B) {
|
|
// for (unsigned i = 0; i < 1024; i++) {
|
|
// A[i+2] = A[i] + 1;
|
|
// B[i+2] = B[i] + 1;
|
|
// }
|
|
// }
|
|
//
|
|
// This case is currently unsafe according to the max safe distance. If we
|
|
// analyze the two accesses on array B, the max safe dependence distance
|
|
// is 2. Then we analyze the accesses on array A, the minimum distance needed
|
|
// is 8, which is less than 2 and forbidden vectorization, But actually
|
|
// both A and B could be vectorized by 2 iterations.
|
|
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 * Stride) << '\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 MaxDependences
|
|
// dependences. In that case return as soon as we find the first
|
|
// unsafe dependence. This puts a limit on this quadratic
|
|
// algorithm.
|
|
if (RecordDependences) {
|
|
if (Type != Dependence::NoDep)
|
|
Dependences.push_back(Dependence(A.second, B.second, Type));
|
|
|
|
if (Dependences.size() >= MaxDependences) {
|
|
RecordDependences = false;
|
|
Dependences.clear();
|
|
DEBUG(dbgs() << "Too many dependences, stopped recording\n");
|
|
}
|
|
}
|
|
if (!RecordDependences && !SafeForVectorization)
|
|
return false;
|
|
}
|
|
++OI;
|
|
}
|
|
AI++;
|
|
}
|
|
}
|
|
|
|
DEBUG(dbgs() << "Total Dependences: " << Dependences.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 = PSE.getSE()->getBackedgeTakenCount(TheLoop);
|
|
if (ExitCount == PSE.getSE()->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;
|
|
|
|
PtrRtChecking.Pointers.clear();
|
|
PtrRtChecking.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, PSE);
|
|
|
|
// 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;
|
|
|
|
MemoryLocation Loc = MemoryLocation::get(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(PSE, Ptr, TheLoop, Strides)) {
|
|
++NumReads;
|
|
IsReadOnlyPtr = true;
|
|
}
|
|
|
|
MemoryLocation Loc = MemoryLocation::get(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();
|
|
|
|
// Find pointers with computable bounds. We are going to use this information
|
|
// to place a runtime bound check.
|
|
bool CanDoRTIfNeeded =
|
|
Accesses.canCheckPtrAtRT(PtrRtChecking, PSE.getSE(), TheLoop, Strides);
|
|
if (!CanDoRTIfNeeded) {
|
|
emitAnalysis(LoopAccessReport() << "cannot identify array bounds");
|
|
DEBUG(dbgs() << "LAA: We can't vectorize because we can't find "
|
|
<< "the array bounds.\n");
|
|
CanVecMem = false;
|
|
return;
|
|
}
|
|
|
|
DEBUG(dbgs() << "LAA: We can perform a memory runtime check if needed.\n");
|
|
|
|
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");
|
|
|
|
// Clear the dependency checks. We assume they are not needed.
|
|
Accesses.resetDepChecks(DepChecker);
|
|
|
|
PtrRtChecking.reset();
|
|
PtrRtChecking.Need = true;
|
|
|
|
auto *SE = PSE.getSE();
|
|
CanDoRTIfNeeded =
|
|
Accesses.canCheckPtrAtRT(PtrRtChecking, SE, TheLoop, Strides, true);
|
|
|
|
// Check that we found the bounds for the pointer.
|
|
if (!CanDoRTIfNeeded) {
|
|
emitAnalysis(LoopAccessReport()
|
|
<< "cannot check memory dependencies at runtime");
|
|
DEBUG(dbgs() << "LAA: Can't vectorize with memory checks\n");
|
|
CanVecMem = false;
|
|
return;
|
|
}
|
|
|
|
CanVecMem = true;
|
|
}
|
|
}
|
|
|
|
if (CanVecMem)
|
|
DEBUG(dbgs() << "LAA: No unsafe dependent memory operations in loop. We"
|
|
<< (PtrRtChecking.Need ? "" : " don't")
|
|
<< " need runtime memory checks.\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 (PSE.getSE()->isLoopInvariant(PSE.getSE()->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;
|
|
}
|
|
|
|
namespace {
|
|
/// \brief IR Values for the lower and upper bounds of a pointer evolution. We
|
|
/// need to use value-handles because SCEV expansion can invalidate previously
|
|
/// expanded values. Thus expansion of a pointer can invalidate the bounds for
|
|
/// a previous one.
|
|
struct PointerBounds {
|
|
TrackingVH<Value> Start;
|
|
TrackingVH<Value> End;
|
|
};
|
|
} // end anonymous namespace
|
|
|
|
/// \brief Expand code for the lower and upper bound of the pointer group \p CG
|
|
/// in \p TheLoop. \return the values for the bounds.
|
|
static PointerBounds
|
|
expandBounds(const RuntimePointerChecking::CheckingPtrGroup *CG, Loop *TheLoop,
|
|
Instruction *Loc, SCEVExpander &Exp, ScalarEvolution *SE,
|
|
const RuntimePointerChecking &PtrRtChecking) {
|
|
Value *Ptr = PtrRtChecking.Pointers[CG->Members[0]].PointerValue;
|
|
const SCEV *Sc = SE->getSCEV(Ptr);
|
|
|
|
if (SE->isLoopInvariant(Sc, TheLoop)) {
|
|
DEBUG(dbgs() << "LAA: Adding RT check for a loop invariant ptr:" << *Ptr
|
|
<< "\n");
|
|
return {Ptr, Ptr};
|
|
} else {
|
|
unsigned AS = Ptr->getType()->getPointerAddressSpace();
|
|
LLVMContext &Ctx = Loc->getContext();
|
|
|
|
// Use this type for pointer arithmetic.
|
|
Type *PtrArithTy = Type::getInt8PtrTy(Ctx, AS);
|
|
Value *Start = nullptr, *End = nullptr;
|
|
|
|
DEBUG(dbgs() << "LAA: Adding RT check for range:\n");
|
|
Start = Exp.expandCodeFor(CG->Low, PtrArithTy, Loc);
|
|
End = Exp.expandCodeFor(CG->High, PtrArithTy, Loc);
|
|
DEBUG(dbgs() << "Start: " << *CG->Low << " End: " << *CG->High << "\n");
|
|
return {Start, End};
|
|
}
|
|
}
|
|
|
|
/// \brief Turns a collection of checks into a collection of expanded upper and
|
|
/// lower bounds for both pointers in the check.
|
|
static SmallVector<std::pair<PointerBounds, PointerBounds>, 4> expandBounds(
|
|
const SmallVectorImpl<RuntimePointerChecking::PointerCheck> &PointerChecks,
|
|
Loop *L, Instruction *Loc, ScalarEvolution *SE, SCEVExpander &Exp,
|
|
const RuntimePointerChecking &PtrRtChecking) {
|
|
SmallVector<std::pair<PointerBounds, PointerBounds>, 4> ChecksWithBounds;
|
|
|
|
// Here we're relying on the SCEV Expander's cache to only emit code for the
|
|
// same bounds once.
|
|
std::transform(
|
|
PointerChecks.begin(), PointerChecks.end(),
|
|
std::back_inserter(ChecksWithBounds),
|
|
[&](const RuntimePointerChecking::PointerCheck &Check) {
|
|
PointerBounds
|
|
First = expandBounds(Check.first, L, Loc, Exp, SE, PtrRtChecking),
|
|
Second = expandBounds(Check.second, L, Loc, Exp, SE, PtrRtChecking);
|
|
return std::make_pair(First, Second);
|
|
});
|
|
|
|
return ChecksWithBounds;
|
|
}
|
|
|
|
std::pair<Instruction *, Instruction *> LoopAccessInfo::addRuntimeChecks(
|
|
Instruction *Loc,
|
|
const SmallVectorImpl<RuntimePointerChecking::PointerCheck> &PointerChecks)
|
|
const {
|
|
auto *SE = PSE.getSE();
|
|
SCEVExpander Exp(*SE, DL, "induction");
|
|
auto ExpandedChecks =
|
|
expandBounds(PointerChecks, TheLoop, Loc, SE, Exp, PtrRtChecking);
|
|
|
|
LLVMContext &Ctx = Loc->getContext();
|
|
Instruction *FirstInst = nullptr;
|
|
IRBuilder<> ChkBuilder(Loc);
|
|
// Our instructions might fold to a constant.
|
|
Value *MemoryRuntimeCheck = nullptr;
|
|
|
|
for (const auto &Check : ExpandedChecks) {
|
|
const PointerBounds &A = Check.first, &B = Check.second;
|
|
// Check if two pointers (A and B) conflict where conflict is computed as:
|
|
// start(A) <= end(B) && start(B) <= end(A)
|
|
unsigned AS0 = A.Start->getType()->getPointerAddressSpace();
|
|
unsigned AS1 = B.Start->getType()->getPointerAddressSpace();
|
|
|
|
assert((AS0 == B.End->getType()->getPointerAddressSpace()) &&
|
|
(AS1 == A.End->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(A.Start, PtrArithTy0, "bc");
|
|
Value *Start1 = ChkBuilder.CreateBitCast(B.Start, PtrArithTy1, "bc");
|
|
Value *End0 = ChkBuilder.CreateBitCast(A.End, PtrArithTy1, "bc");
|
|
Value *End1 = ChkBuilder.CreateBitCast(B.End, 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);
|
|
}
|
|
|
|
std::pair<Instruction *, Instruction *>
|
|
LoopAccessInfo::addRuntimeChecks(Instruction *Loc) const {
|
|
if (!PtrRtChecking.Need)
|
|
return std::make_pair(nullptr, nullptr);
|
|
|
|
return addRuntimeChecks(Loc, PtrRtChecking.getChecks());
|
|
}
|
|
|
|
LoopAccessInfo::LoopAccessInfo(Loop *L, ScalarEvolution *SE,
|
|
const DataLayout &DL,
|
|
const TargetLibraryInfo *TLI, AliasAnalysis *AA,
|
|
DominatorTree *DT, LoopInfo *LI,
|
|
const ValueToValueMap &Strides)
|
|
: PSE(*SE), PtrRtChecking(SE), DepChecker(PSE, L), TheLoop(L), 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 (PtrRtChecking.Need)
|
|
OS.indent(Depth) << "Memory dependences are safe with run-time checks\n";
|
|
else
|
|
OS.indent(Depth) << "Memory dependences are safe\n";
|
|
}
|
|
|
|
if (Report)
|
|
OS.indent(Depth) << "Report: " << Report->str() << "\n";
|
|
|
|
if (auto *Dependences = DepChecker.getDependences()) {
|
|
OS.indent(Depth) << "Dependences:\n";
|
|
for (auto &Dep : *Dependences) {
|
|
Dep.print(OS, Depth + 2, DepChecker.getMemoryInstructions());
|
|
OS << "\n";
|
|
}
|
|
} else
|
|
OS.indent(Depth) << "Too many dependences, not recorded\n";
|
|
|
|
// List the pair of accesses need run-time checks to prove independence.
|
|
PtrRtChecking.print(OS, Depth);
|
|
OS << "\n";
|
|
|
|
OS.indent(Depth) << "Store to invariant address was "
|
|
<< (StoreToLoopInvariantAddress ? "" : "not ")
|
|
<< "found in loop.\n";
|
|
|
|
OS.indent(Depth) << "SCEV assumptions:\n";
|
|
PSE.getUnionPredicate().print(OS, Depth);
|
|
}
|
|
|
|
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<ScalarEvolutionWrapperPass>().getSE();
|
|
auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
|
|
TLI = TLIP ? &TLIP->getTLI() : nullptr;
|
|
AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
|
|
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
|
|
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
|
|
|
|
return false;
|
|
}
|
|
|
|
void LoopAccessAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
|
|
AU.addRequired<ScalarEvolutionWrapperPass>();
|
|
AU.addRequired<AAResultsWrapperPass>();
|
|
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_PASS_DEPENDENCY(AAResultsWrapperPass)
|
|
INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
|
|
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();
|
|
}
|
|
}
|