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Diffstat (limited to 'contrib/llvm/lib/Transforms/Utils/MemorySSA.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Utils/MemorySSA.cpp | 2305 |
1 files changed, 2305 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/Utils/MemorySSA.cpp b/contrib/llvm/lib/Transforms/Utils/MemorySSA.cpp new file mode 100644 index 000000000000..1ce4225f09cc --- /dev/null +++ b/contrib/llvm/lib/Transforms/Utils/MemorySSA.cpp @@ -0,0 +1,2305 @@ +//===-- MemorySSA.cpp - Memory SSA Builder---------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------===// +// +// This file implements the MemorySSA class. +// +//===----------------------------------------------------------------===// +#include "llvm/Transforms/Utils/MemorySSA.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/DenseSet.h" +#include "llvm/ADT/DepthFirstIterator.h" +#include "llvm/ADT/GraphTraits.h" +#include "llvm/ADT/PostOrderIterator.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SmallBitVector.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallSet.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/CFG.h" +#include "llvm/Analysis/GlobalsModRef.h" +#include "llvm/Analysis/IteratedDominanceFrontier.h" +#include "llvm/Analysis/MemoryLocation.h" +#include "llvm/Analysis/PHITransAddr.h" +#include "llvm/IR/AssemblyAnnotationWriter.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/GlobalVariable.h" +#include "llvm/IR/IRBuilder.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/IR/Metadata.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/PatternMatch.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/FormattedStream.h" +#include "llvm/Transforms/Scalar.h" +#include <algorithm> + +#define DEBUG_TYPE "memoryssa" +using namespace llvm; +STATISTIC(NumClobberCacheLookups, "Number of Memory SSA version cache lookups"); +STATISTIC(NumClobberCacheHits, "Number of Memory SSA version cache hits"); +STATISTIC(NumClobberCacheInserts, "Number of MemorySSA version cache inserts"); + +INITIALIZE_PASS_BEGIN(MemorySSAWrapperPass, "memoryssa", "Memory SSA", false, + true) +INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) +INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass) +INITIALIZE_PASS_END(MemorySSAWrapperPass, "memoryssa", "Memory SSA", false, + true) + +INITIALIZE_PASS_BEGIN(MemorySSAPrinterLegacyPass, "print-memoryssa", + "Memory SSA Printer", false, false) +INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass) +INITIALIZE_PASS_END(MemorySSAPrinterLegacyPass, "print-memoryssa", + "Memory SSA Printer", false, false) + +static cl::opt<unsigned> MaxCheckLimit( + "memssa-check-limit", cl::Hidden, cl::init(100), + cl::desc("The maximum number of stores/phis MemorySSA" + "will consider trying to walk past (default = 100)")); + +static cl::opt<bool> + VerifyMemorySSA("verify-memoryssa", cl::init(false), cl::Hidden, + cl::desc("Verify MemorySSA in legacy printer pass.")); + +namespace llvm { +/// \brief An assembly annotator class to print Memory SSA information in +/// comments. +class MemorySSAAnnotatedWriter : public AssemblyAnnotationWriter { + friend class MemorySSA; + const MemorySSA *MSSA; + +public: + MemorySSAAnnotatedWriter(const MemorySSA *M) : MSSA(M) {} + + virtual void emitBasicBlockStartAnnot(const BasicBlock *BB, + formatted_raw_ostream &OS) { + if (MemoryAccess *MA = MSSA->getMemoryAccess(BB)) + OS << "; " << *MA << "\n"; + } + + virtual void emitInstructionAnnot(const Instruction *I, + formatted_raw_ostream &OS) { + if (MemoryAccess *MA = MSSA->getMemoryAccess(I)) + OS << "; " << *MA << "\n"; + } +}; +} + +namespace { +/// Our current alias analysis API differentiates heavily between calls and +/// non-calls, and functions called on one usually assert on the other. +/// This class encapsulates the distinction to simplify other code that wants +/// "Memory affecting instructions and related data" to use as a key. +/// For example, this class is used as a densemap key in the use optimizer. +class MemoryLocOrCall { +public: + MemoryLocOrCall() : IsCall(false) {} + MemoryLocOrCall(MemoryUseOrDef *MUD) + : MemoryLocOrCall(MUD->getMemoryInst()) {} + MemoryLocOrCall(const MemoryUseOrDef *MUD) + : MemoryLocOrCall(MUD->getMemoryInst()) {} + + MemoryLocOrCall(Instruction *Inst) { + if (ImmutableCallSite(Inst)) { + IsCall = true; + CS = ImmutableCallSite(Inst); + } else { + IsCall = false; + // There is no such thing as a memorylocation for a fence inst, and it is + // unique in that regard. + if (!isa<FenceInst>(Inst)) + Loc = MemoryLocation::get(Inst); + } + } + + explicit MemoryLocOrCall(const MemoryLocation &Loc) + : IsCall(false), Loc(Loc) {} + + bool IsCall; + ImmutableCallSite getCS() const { + assert(IsCall); + return CS; + } + MemoryLocation getLoc() const { + assert(!IsCall); + return Loc; + } + + bool operator==(const MemoryLocOrCall &Other) const { + if (IsCall != Other.IsCall) + return false; + + if (IsCall) + return CS.getCalledValue() == Other.CS.getCalledValue(); + return Loc == Other.Loc; + } + +private: + union { + ImmutableCallSite CS; + MemoryLocation Loc; + }; +}; +} + +namespace llvm { +template <> struct DenseMapInfo<MemoryLocOrCall> { + static inline MemoryLocOrCall getEmptyKey() { + return MemoryLocOrCall(DenseMapInfo<MemoryLocation>::getEmptyKey()); + } + static inline MemoryLocOrCall getTombstoneKey() { + return MemoryLocOrCall(DenseMapInfo<MemoryLocation>::getTombstoneKey()); + } + static unsigned getHashValue(const MemoryLocOrCall &MLOC) { + if (MLOC.IsCall) + return hash_combine(MLOC.IsCall, + DenseMapInfo<const Value *>::getHashValue( + MLOC.getCS().getCalledValue())); + return hash_combine( + MLOC.IsCall, DenseMapInfo<MemoryLocation>::getHashValue(MLOC.getLoc())); + } + static bool isEqual(const MemoryLocOrCall &LHS, const MemoryLocOrCall &RHS) { + return LHS == RHS; + } +}; + +enum class Reorderability { Always, IfNoAlias, Never }; + +/// This does one-way checks to see if Use could theoretically be hoisted above +/// MayClobber. This will not check the other way around. +/// +/// This assumes that, for the purposes of MemorySSA, Use comes directly after +/// MayClobber, with no potentially clobbering operations in between them. +/// (Where potentially clobbering ops are memory barriers, aliased stores, etc.) +static Reorderability getLoadReorderability(const LoadInst *Use, + const LoadInst *MayClobber) { + bool VolatileUse = Use->isVolatile(); + bool VolatileClobber = MayClobber->isVolatile(); + // Volatile operations may never be reordered with other volatile operations. + if (VolatileUse && VolatileClobber) + return Reorderability::Never; + + // The lang ref allows reordering of volatile and non-volatile operations. + // Whether an aliasing nonvolatile load and volatile load can be reordered, + // though, is ambiguous. Because it may not be best to exploit this ambiguity, + // we only allow volatile/non-volatile reordering if the volatile and + // non-volatile operations don't alias. + Reorderability Result = VolatileUse || VolatileClobber + ? Reorderability::IfNoAlias + : Reorderability::Always; + + // If a load is seq_cst, it cannot be moved above other loads. If its ordering + // is weaker, it can be moved above other loads. We just need to be sure that + // MayClobber isn't an acquire load, because loads can't be moved above + // acquire loads. + // + // Note that this explicitly *does* allow the free reordering of monotonic (or + // weaker) loads of the same address. + bool SeqCstUse = Use->getOrdering() == AtomicOrdering::SequentiallyConsistent; + bool MayClobberIsAcquire = isAtLeastOrStrongerThan(MayClobber->getOrdering(), + AtomicOrdering::Acquire); + if (SeqCstUse || MayClobberIsAcquire) + return Reorderability::Never; + return Result; +} + +static bool instructionClobbersQuery(MemoryDef *MD, + const MemoryLocation &UseLoc, + const Instruction *UseInst, + AliasAnalysis &AA) { + Instruction *DefInst = MD->getMemoryInst(); + assert(DefInst && "Defining instruction not actually an instruction"); + + if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(DefInst)) { + // These intrinsics will show up as affecting memory, but they are just + // markers. + switch (II->getIntrinsicID()) { + case Intrinsic::lifetime_start: + case Intrinsic::lifetime_end: + case Intrinsic::invariant_start: + case Intrinsic::invariant_end: + case Intrinsic::assume: + return false; + default: + break; + } + } + + ImmutableCallSite UseCS(UseInst); + if (UseCS) { + ModRefInfo I = AA.getModRefInfo(DefInst, UseCS); + return I != MRI_NoModRef; + } + + if (auto *DefLoad = dyn_cast<LoadInst>(DefInst)) { + if (auto *UseLoad = dyn_cast<LoadInst>(UseInst)) { + switch (getLoadReorderability(UseLoad, DefLoad)) { + case Reorderability::Always: + return false; + case Reorderability::Never: + return true; + case Reorderability::IfNoAlias: + return !AA.isNoAlias(UseLoc, MemoryLocation::get(DefLoad)); + } + } + } + + return AA.getModRefInfo(DefInst, UseLoc) & MRI_Mod; +} + +static bool instructionClobbersQuery(MemoryDef *MD, const MemoryUseOrDef *MU, + const MemoryLocOrCall &UseMLOC, + AliasAnalysis &AA) { + // FIXME: This is a temporary hack to allow a single instructionClobbersQuery + // to exist while MemoryLocOrCall is pushed through places. + if (UseMLOC.IsCall) + return instructionClobbersQuery(MD, MemoryLocation(), MU->getMemoryInst(), + AA); + return instructionClobbersQuery(MD, UseMLOC.getLoc(), MU->getMemoryInst(), + AA); +} + +// Return true when MD may alias MU, return false otherwise. +bool defClobbersUseOrDef(MemoryDef *MD, const MemoryUseOrDef *MU, + AliasAnalysis &AA) { + return instructionClobbersQuery(MD, MU, MemoryLocOrCall(MU), AA); +} +} + +namespace { +struct UpwardsMemoryQuery { + // True if our original query started off as a call + bool IsCall; + // The pointer location we started the query with. This will be empty if + // IsCall is true. + MemoryLocation StartingLoc; + // This is the instruction we were querying about. + const Instruction *Inst; + // The MemoryAccess we actually got called with, used to test local domination + const MemoryAccess *OriginalAccess; + + UpwardsMemoryQuery() + : IsCall(false), Inst(nullptr), OriginalAccess(nullptr) {} + + UpwardsMemoryQuery(const Instruction *Inst, const MemoryAccess *Access) + : IsCall(ImmutableCallSite(Inst)), Inst(Inst), OriginalAccess(Access) { + if (!IsCall) + StartingLoc = MemoryLocation::get(Inst); + } +}; + +static bool lifetimeEndsAt(MemoryDef *MD, const MemoryLocation &Loc, + AliasAnalysis &AA) { + Instruction *Inst = MD->getMemoryInst(); + if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) { + switch (II->getIntrinsicID()) { + case Intrinsic::lifetime_start: + case Intrinsic::lifetime_end: + return AA.isMustAlias(MemoryLocation(II->getArgOperand(1)), Loc); + default: + return false; + } + } + return false; +} + +static bool isUseTriviallyOptimizableToLiveOnEntry(AliasAnalysis &AA, + const Instruction *I) { + // If the memory can't be changed, then loads of the memory can't be + // clobbered. + // + // FIXME: We should handle invariant groups, as well. It's a bit harder, + // because we need to pay close attention to invariant group barriers. + return isa<LoadInst>(I) && (I->getMetadata(LLVMContext::MD_invariant_load) || + AA.pointsToConstantMemory(I)); +} + +/// Cache for our caching MemorySSA walker. +class WalkerCache { + DenseMap<ConstMemoryAccessPair, MemoryAccess *> Accesses; + DenseMap<const MemoryAccess *, MemoryAccess *> Calls; + +public: + MemoryAccess *lookup(const MemoryAccess *MA, const MemoryLocation &Loc, + bool IsCall) const { + ++NumClobberCacheLookups; + MemoryAccess *R = IsCall ? Calls.lookup(MA) : Accesses.lookup({MA, Loc}); + if (R) + ++NumClobberCacheHits; + return R; + } + + bool insert(const MemoryAccess *MA, MemoryAccess *To, + const MemoryLocation &Loc, bool IsCall) { + // This is fine for Phis, since there are times where we can't optimize + // them. Making a def its own clobber is never correct, though. + assert((MA != To || isa<MemoryPhi>(MA)) && + "Something can't clobber itself!"); + + ++NumClobberCacheInserts; + bool Inserted; + if (IsCall) + Inserted = Calls.insert({MA, To}).second; + else + Inserted = Accesses.insert({{MA, Loc}, To}).second; + + return Inserted; + } + + bool remove(const MemoryAccess *MA, const MemoryLocation &Loc, bool IsCall) { + return IsCall ? Calls.erase(MA) : Accesses.erase({MA, Loc}); + } + + void clear() { + Accesses.clear(); + Calls.clear(); + } + + bool contains(const MemoryAccess *MA) const { + for (auto &P : Accesses) + if (P.first.first == MA || P.second == MA) + return true; + for (auto &P : Calls) + if (P.first == MA || P.second == MA) + return true; + return false; + } +}; + +/// Walks the defining uses of MemoryDefs. Stops after we hit something that has +/// no defining use (e.g. a MemoryPhi or liveOnEntry). Note that, when comparing +/// against a null def_chain_iterator, this will compare equal only after +/// walking said Phi/liveOnEntry. +struct def_chain_iterator + : public iterator_facade_base<def_chain_iterator, std::forward_iterator_tag, + MemoryAccess *> { + def_chain_iterator() : MA(nullptr) {} + def_chain_iterator(MemoryAccess *MA) : MA(MA) {} + + MemoryAccess *operator*() const { return MA; } + + def_chain_iterator &operator++() { + // N.B. liveOnEntry has a null defining access. + if (auto *MUD = dyn_cast<MemoryUseOrDef>(MA)) + MA = MUD->getDefiningAccess(); + else + MA = nullptr; + return *this; + } + + bool operator==(const def_chain_iterator &O) const { return MA == O.MA; } + +private: + MemoryAccess *MA; +}; + +static iterator_range<def_chain_iterator> +def_chain(MemoryAccess *MA, MemoryAccess *UpTo = nullptr) { +#ifdef EXPENSIVE_CHECKS + assert((!UpTo || find(def_chain(MA), UpTo) != def_chain_iterator()) && + "UpTo isn't in the def chain!"); +#endif + return make_range(def_chain_iterator(MA), def_chain_iterator(UpTo)); +} + +/// Verifies that `Start` is clobbered by `ClobberAt`, and that nothing +/// inbetween `Start` and `ClobberAt` can clobbers `Start`. +/// +/// This is meant to be as simple and self-contained as possible. Because it +/// uses no cache, etc., it can be relatively expensive. +/// +/// \param Start The MemoryAccess that we want to walk from. +/// \param ClobberAt A clobber for Start. +/// \param StartLoc The MemoryLocation for Start. +/// \param MSSA The MemorySSA isntance that Start and ClobberAt belong to. +/// \param Query The UpwardsMemoryQuery we used for our search. +/// \param AA The AliasAnalysis we used for our search. +static void LLVM_ATTRIBUTE_UNUSED +checkClobberSanity(MemoryAccess *Start, MemoryAccess *ClobberAt, + const MemoryLocation &StartLoc, const MemorySSA &MSSA, + const UpwardsMemoryQuery &Query, AliasAnalysis &AA) { + assert(MSSA.dominates(ClobberAt, Start) && "Clobber doesn't dominate start?"); + + if (MSSA.isLiveOnEntryDef(Start)) { + assert(MSSA.isLiveOnEntryDef(ClobberAt) && + "liveOnEntry must clobber itself"); + return; + } + + bool FoundClobber = false; + DenseSet<MemoryAccessPair> VisitedPhis; + SmallVector<MemoryAccessPair, 8> Worklist; + Worklist.emplace_back(Start, StartLoc); + // Walk all paths from Start to ClobberAt, while looking for clobbers. If one + // is found, complain. + while (!Worklist.empty()) { + MemoryAccessPair MAP = Worklist.pop_back_val(); + // All we care about is that nothing from Start to ClobberAt clobbers Start. + // We learn nothing from revisiting nodes. + if (!VisitedPhis.insert(MAP).second) + continue; + + for (MemoryAccess *MA : def_chain(MAP.first)) { + if (MA == ClobberAt) { + if (auto *MD = dyn_cast<MemoryDef>(MA)) { + // instructionClobbersQuery isn't essentially free, so don't use `|=`, + // since it won't let us short-circuit. + // + // Also, note that this can't be hoisted out of the `Worklist` loop, + // since MD may only act as a clobber for 1 of N MemoryLocations. + FoundClobber = + FoundClobber || MSSA.isLiveOnEntryDef(MD) || + instructionClobbersQuery(MD, MAP.second, Query.Inst, AA); + } + break; + } + + // We should never hit liveOnEntry, unless it's the clobber. + assert(!MSSA.isLiveOnEntryDef(MA) && "Hit liveOnEntry before clobber?"); + + if (auto *MD = dyn_cast<MemoryDef>(MA)) { + (void)MD; + assert(!instructionClobbersQuery(MD, MAP.second, Query.Inst, AA) && + "Found clobber before reaching ClobberAt!"); + continue; + } + + assert(isa<MemoryPhi>(MA)); + Worklist.append(upward_defs_begin({MA, MAP.second}), upward_defs_end()); + } + } + + // If ClobberAt is a MemoryPhi, we can assume something above it acted as a + // clobber. Otherwise, `ClobberAt` should've acted as a clobber at some point. + assert((isa<MemoryPhi>(ClobberAt) || FoundClobber) && + "ClobberAt never acted as a clobber"); +} + +/// Our algorithm for walking (and trying to optimize) clobbers, all wrapped up +/// in one class. +class ClobberWalker { + /// Save a few bytes by using unsigned instead of size_t. + using ListIndex = unsigned; + + /// Represents a span of contiguous MemoryDefs, potentially ending in a + /// MemoryPhi. + struct DefPath { + MemoryLocation Loc; + // Note that, because we always walk in reverse, Last will always dominate + // First. Also note that First and Last are inclusive. + MemoryAccess *First; + MemoryAccess *Last; + Optional<ListIndex> Previous; + + DefPath(const MemoryLocation &Loc, MemoryAccess *First, MemoryAccess *Last, + Optional<ListIndex> Previous) + : Loc(Loc), First(First), Last(Last), Previous(Previous) {} + + DefPath(const MemoryLocation &Loc, MemoryAccess *Init, + Optional<ListIndex> Previous) + : DefPath(Loc, Init, Init, Previous) {} + }; + + const MemorySSA &MSSA; + AliasAnalysis &AA; + DominatorTree &DT; + WalkerCache &WC; + UpwardsMemoryQuery *Query; + bool UseCache; + + // Phi optimization bookkeeping + SmallVector<DefPath, 32> Paths; + DenseSet<ConstMemoryAccessPair> VisitedPhis; + DenseMap<const BasicBlock *, MemoryAccess *> WalkTargetCache; + + void setUseCache(bool Use) { UseCache = Use; } + bool shouldIgnoreCache() const { + // UseCache will only be false when we're debugging, or when expensive + // checks are enabled. In either case, we don't care deeply about speed. + return LLVM_UNLIKELY(!UseCache); + } + + void addCacheEntry(const MemoryAccess *What, MemoryAccess *To, + const MemoryLocation &Loc) const { +// EXPENSIVE_CHECKS because most of these queries are redundant. +#ifdef EXPENSIVE_CHECKS + assert(MSSA.dominates(To, What)); +#endif + if (shouldIgnoreCache()) + return; + WC.insert(What, To, Loc, Query->IsCall); + } + + MemoryAccess *lookupCache(const MemoryAccess *MA, const MemoryLocation &Loc) { + return shouldIgnoreCache() ? nullptr : WC.lookup(MA, Loc, Query->IsCall); + } + + void cacheDefPath(const DefPath &DN, MemoryAccess *Target) const { + if (shouldIgnoreCache()) + return; + + for (MemoryAccess *MA : def_chain(DN.First, DN.Last)) + addCacheEntry(MA, Target, DN.Loc); + + // DefPaths only express the path we walked. So, DN.Last could either be a + // thing we want to cache, or not. + if (DN.Last != Target) + addCacheEntry(DN.Last, Target, DN.Loc); + } + + /// Find the nearest def or phi that `From` can legally be optimized to. + /// + /// FIXME: Deduplicate this with MSSA::findDominatingDef. Ideally, MSSA should + /// keep track of this information for us, and allow us O(1) lookups of this + /// info. + MemoryAccess *getWalkTarget(const MemoryPhi *From) { + assert(From->getNumOperands() && "Phi with no operands?"); + + BasicBlock *BB = From->getBlock(); + auto At = WalkTargetCache.find(BB); + if (At != WalkTargetCache.end()) + return At->second; + + SmallVector<const BasicBlock *, 8> ToCache; + ToCache.push_back(BB); + + MemoryAccess *Result = MSSA.getLiveOnEntryDef(); + DomTreeNode *Node = DT.getNode(BB); + while ((Node = Node->getIDom())) { + auto At = WalkTargetCache.find(BB); + if (At != WalkTargetCache.end()) { + Result = At->second; + break; + } + + auto *Accesses = MSSA.getBlockAccesses(Node->getBlock()); + if (Accesses) { + auto Iter = find_if(reverse(*Accesses), [](const MemoryAccess &MA) { + return !isa<MemoryUse>(MA); + }); + if (Iter != Accesses->rend()) { + Result = const_cast<MemoryAccess *>(&*Iter); + break; + } + } + + ToCache.push_back(Node->getBlock()); + } + + for (const BasicBlock *BB : ToCache) + WalkTargetCache.insert({BB, Result}); + return Result; + } + + /// Result of calling walkToPhiOrClobber. + struct UpwardsWalkResult { + /// The "Result" of the walk. Either a clobber, the last thing we walked, or + /// both. + MemoryAccess *Result; + bool IsKnownClobber; + bool FromCache; + }; + + /// Walk to the next Phi or Clobber in the def chain starting at Desc.Last. + /// This will update Desc.Last as it walks. It will (optionally) also stop at + /// StopAt. + /// + /// This does not test for whether StopAt is a clobber + UpwardsWalkResult walkToPhiOrClobber(DefPath &Desc, + MemoryAccess *StopAt = nullptr) { + assert(!isa<MemoryUse>(Desc.Last) && "Uses don't exist in my world"); + + for (MemoryAccess *Current : def_chain(Desc.Last)) { + Desc.Last = Current; + if (Current == StopAt) + return {Current, false, false}; + + if (auto *MD = dyn_cast<MemoryDef>(Current)) + if (MSSA.isLiveOnEntryDef(MD) || + instructionClobbersQuery(MD, Desc.Loc, Query->Inst, AA)) + return {MD, true, false}; + + // Cache checks must be done last, because if Current is a clobber, the + // cache will contain the clobber for Current. + if (MemoryAccess *MA = lookupCache(Current, Desc.Loc)) + return {MA, true, true}; + } + + assert(isa<MemoryPhi>(Desc.Last) && + "Ended at a non-clobber that's not a phi?"); + return {Desc.Last, false, false}; + } + + void addSearches(MemoryPhi *Phi, SmallVectorImpl<ListIndex> &PausedSearches, + ListIndex PriorNode) { + auto UpwardDefs = make_range(upward_defs_begin({Phi, Paths[PriorNode].Loc}), + upward_defs_end()); + for (const MemoryAccessPair &P : UpwardDefs) { + PausedSearches.push_back(Paths.size()); + Paths.emplace_back(P.second, P.first, PriorNode); + } + } + + /// Represents a search that terminated after finding a clobber. This clobber + /// may or may not be present in the path of defs from LastNode..SearchStart, + /// since it may have been retrieved from cache. + struct TerminatedPath { + MemoryAccess *Clobber; + ListIndex LastNode; + }; + + /// Get an access that keeps us from optimizing to the given phi. + /// + /// PausedSearches is an array of indices into the Paths array. Its incoming + /// value is the indices of searches that stopped at the last phi optimization + /// target. It's left in an unspecified state. + /// + /// If this returns None, NewPaused is a vector of searches that terminated + /// at StopWhere. Otherwise, NewPaused is left in an unspecified state. + Optional<TerminatedPath> + getBlockingAccess(MemoryAccess *StopWhere, + SmallVectorImpl<ListIndex> &PausedSearches, + SmallVectorImpl<ListIndex> &NewPaused, + SmallVectorImpl<TerminatedPath> &Terminated) { + assert(!PausedSearches.empty() && "No searches to continue?"); + + // BFS vs DFS really doesn't make a difference here, so just do a DFS with + // PausedSearches as our stack. + while (!PausedSearches.empty()) { + ListIndex PathIndex = PausedSearches.pop_back_val(); + DefPath &Node = Paths[PathIndex]; + + // If we've already visited this path with this MemoryLocation, we don't + // need to do so again. + // + // NOTE: That we just drop these paths on the ground makes caching + // behavior sporadic. e.g. given a diamond: + // A + // B C + // D + // + // ...If we walk D, B, A, C, we'll only cache the result of phi + // optimization for A, B, and D; C will be skipped because it dies here. + // This arguably isn't the worst thing ever, since: + // - We generally query things in a top-down order, so if we got below D + // without needing cache entries for {C, MemLoc}, then chances are + // that those cache entries would end up ultimately unused. + // - We still cache things for A, so C only needs to walk up a bit. + // If this behavior becomes problematic, we can fix without a ton of extra + // work. + if (!VisitedPhis.insert({Node.Last, Node.Loc}).second) + continue; + + UpwardsWalkResult Res = walkToPhiOrClobber(Node, /*StopAt=*/StopWhere); + if (Res.IsKnownClobber) { + assert(Res.Result != StopWhere || Res.FromCache); + // If this wasn't a cache hit, we hit a clobber when walking. That's a + // failure. + TerminatedPath Term{Res.Result, PathIndex}; + if (!Res.FromCache || !MSSA.dominates(Res.Result, StopWhere)) + return Term; + + // Otherwise, it's a valid thing to potentially optimize to. + Terminated.push_back(Term); + continue; + } + + if (Res.Result == StopWhere) { + // We've hit our target. Save this path off for if we want to continue + // walking. + NewPaused.push_back(PathIndex); + continue; + } + + assert(!MSSA.isLiveOnEntryDef(Res.Result) && "liveOnEntry is a clobber"); + addSearches(cast<MemoryPhi>(Res.Result), PausedSearches, PathIndex); + } + + return None; + } + + template <typename T, typename Walker> + struct generic_def_path_iterator + : public iterator_facade_base<generic_def_path_iterator<T, Walker>, + std::forward_iterator_tag, T *> { + generic_def_path_iterator() : W(nullptr), N(None) {} + generic_def_path_iterator(Walker *W, ListIndex N) : W(W), N(N) {} + + T &operator*() const { return curNode(); } + + generic_def_path_iterator &operator++() { + N = curNode().Previous; + return *this; + } + + bool operator==(const generic_def_path_iterator &O) const { + if (N.hasValue() != O.N.hasValue()) + return false; + return !N.hasValue() || *N == *O.N; + } + + private: + T &curNode() const { return W->Paths[*N]; } + + Walker *W; + Optional<ListIndex> N; + }; + + using def_path_iterator = generic_def_path_iterator<DefPath, ClobberWalker>; + using const_def_path_iterator = + generic_def_path_iterator<const DefPath, const ClobberWalker>; + + iterator_range<def_path_iterator> def_path(ListIndex From) { + return make_range(def_path_iterator(this, From), def_path_iterator()); + } + + iterator_range<const_def_path_iterator> const_def_path(ListIndex From) const { + return make_range(const_def_path_iterator(this, From), + const_def_path_iterator()); + } + + struct OptznResult { + /// The path that contains our result. + TerminatedPath PrimaryClobber; + /// The paths that we can legally cache back from, but that aren't + /// necessarily the result of the Phi optimization. + SmallVector<TerminatedPath, 4> OtherClobbers; + }; + + ListIndex defPathIndex(const DefPath &N) const { + // The assert looks nicer if we don't need to do &N + const DefPath *NP = &N; + assert(!Paths.empty() && NP >= &Paths.front() && NP <= &Paths.back() && + "Out of bounds DefPath!"); + return NP - &Paths.front(); + } + + /// Try to optimize a phi as best as we can. Returns a SmallVector of Paths + /// that act as legal clobbers. Note that this won't return *all* clobbers. + /// + /// Phi optimization algorithm tl;dr: + /// - Find the earliest def/phi, A, we can optimize to + /// - Find if all paths from the starting memory access ultimately reach A + /// - If not, optimization isn't possible. + /// - Otherwise, walk from A to another clobber or phi, A'. + /// - If A' is a def, we're done. + /// - If A' is a phi, try to optimize it. + /// + /// A path is a series of {MemoryAccess, MemoryLocation} pairs. A path + /// terminates when a MemoryAccess that clobbers said MemoryLocation is found. + OptznResult tryOptimizePhi(MemoryPhi *Phi, MemoryAccess *Start, + const MemoryLocation &Loc) { + assert(Paths.empty() && VisitedPhis.empty() && + "Reset the optimization state."); + + Paths.emplace_back(Loc, Start, Phi, None); + // Stores how many "valid" optimization nodes we had prior to calling + // addSearches/getBlockingAccess. Necessary for caching if we had a blocker. + auto PriorPathsSize = Paths.size(); + + SmallVector<ListIndex, 16> PausedSearches; + SmallVector<ListIndex, 8> NewPaused; + SmallVector<TerminatedPath, 4> TerminatedPaths; + + addSearches(Phi, PausedSearches, 0); + + // Moves the TerminatedPath with the "most dominated" Clobber to the end of + // Paths. + auto MoveDominatedPathToEnd = [&](SmallVectorImpl<TerminatedPath> &Paths) { + assert(!Paths.empty() && "Need a path to move"); + auto Dom = Paths.begin(); + for (auto I = std::next(Dom), E = Paths.end(); I != E; ++I) + if (!MSSA.dominates(I->Clobber, Dom->Clobber)) + Dom = I; + auto Last = Paths.end() - 1; + if (Last != Dom) + std::iter_swap(Last, Dom); + }; + + MemoryPhi *Current = Phi; + while (1) { + assert(!MSSA.isLiveOnEntryDef(Current) && + "liveOnEntry wasn't treated as a clobber?"); + + MemoryAccess *Target = getWalkTarget(Current); + // If a TerminatedPath doesn't dominate Target, then it wasn't a legal + // optimization for the prior phi. + assert(all_of(TerminatedPaths, [&](const TerminatedPath &P) { + return MSSA.dominates(P.Clobber, Target); + })); + + // FIXME: This is broken, because the Blocker may be reported to be + // liveOnEntry, and we'll happily wait for that to disappear (read: never) + // For the moment, this is fine, since we do nothing with blocker info. + if (Optional<TerminatedPath> Blocker = getBlockingAccess( + Target, PausedSearches, NewPaused, TerminatedPaths)) { + // Cache our work on the blocking node, since we know that's correct. + cacheDefPath(Paths[Blocker->LastNode], Blocker->Clobber); + + // Find the node we started at. We can't search based on N->Last, since + // we may have gone around a loop with a different MemoryLocation. + auto Iter = find_if(def_path(Blocker->LastNode), [&](const DefPath &N) { + return defPathIndex(N) < PriorPathsSize; + }); + assert(Iter != def_path_iterator()); + + DefPath &CurNode = *Iter; + assert(CurNode.Last == Current); + + // Two things: + // A. We can't reliably cache all of NewPaused back. Consider a case + // where we have two paths in NewPaused; one of which can't optimize + // above this phi, whereas the other can. If we cache the second path + // back, we'll end up with suboptimal cache entries. We can handle + // cases like this a bit better when we either try to find all + // clobbers that block phi optimization, or when our cache starts + // supporting unfinished searches. + // B. We can't reliably cache TerminatedPaths back here without doing + // extra checks; consider a case like: + // T + // / \ + // D C + // \ / + // S + // Where T is our target, C is a node with a clobber on it, D is a + // diamond (with a clobber *only* on the left or right node, N), and + // S is our start. Say we walk to D, through the node opposite N + // (read: ignoring the clobber), and see a cache entry in the top + // node of D. That cache entry gets put into TerminatedPaths. We then + // walk up to C (N is later in our worklist), find the clobber, and + // quit. If we append TerminatedPaths to OtherClobbers, we'll cache + // the bottom part of D to the cached clobber, ignoring the clobber + // in N. Again, this problem goes away if we start tracking all + // blockers for a given phi optimization. + TerminatedPath Result{CurNode.Last, defPathIndex(CurNode)}; + return {Result, {}}; + } + + // If there's nothing left to search, then all paths led to valid clobbers + // that we got from our cache; pick the nearest to the start, and allow + // the rest to be cached back. + if (NewPaused.empty()) { + MoveDominatedPathToEnd(TerminatedPaths); + TerminatedPath Result = TerminatedPaths.pop_back_val(); + return {Result, std::move(TerminatedPaths)}; + } + + MemoryAccess *DefChainEnd = nullptr; + SmallVector<TerminatedPath, 4> Clobbers; + for (ListIndex Paused : NewPaused) { + UpwardsWalkResult WR = walkToPhiOrClobber(Paths[Paused]); + if (WR.IsKnownClobber) + Clobbers.push_back({WR.Result, Paused}); + else + // Micro-opt: If we hit the end of the chain, save it. + DefChainEnd = WR.Result; + } + + if (!TerminatedPaths.empty()) { + // If we couldn't find the dominating phi/liveOnEntry in the above loop, + // do it now. + if (!DefChainEnd) + for (MemoryAccess *MA : def_chain(Target)) + DefChainEnd = MA; + + // If any of the terminated paths don't dominate the phi we'll try to + // optimize, we need to figure out what they are and quit. + const BasicBlock *ChainBB = DefChainEnd->getBlock(); + for (const TerminatedPath &TP : TerminatedPaths) { + // Because we know that DefChainEnd is as "high" as we can go, we + // don't need local dominance checks; BB dominance is sufficient. + if (DT.dominates(ChainBB, TP.Clobber->getBlock())) + Clobbers.push_back(TP); + } + } + + // If we have clobbers in the def chain, find the one closest to Current + // and quit. + if (!Clobbers.empty()) { + MoveDominatedPathToEnd(Clobbers); + TerminatedPath Result = Clobbers.pop_back_val(); + return {Result, std::move(Clobbers)}; + } + + assert(all_of(NewPaused, + [&](ListIndex I) { return Paths[I].Last == DefChainEnd; })); + + // Because liveOnEntry is a clobber, this must be a phi. + auto *DefChainPhi = cast<MemoryPhi>(DefChainEnd); + + PriorPathsSize = Paths.size(); + PausedSearches.clear(); + for (ListIndex I : NewPaused) + addSearches(DefChainPhi, PausedSearches, I); + NewPaused.clear(); + + Current = DefChainPhi; + } + } + + /// Caches everything in an OptznResult. + void cacheOptResult(const OptznResult &R) { + if (R.OtherClobbers.empty()) { + // If we're not going to be caching OtherClobbers, don't bother with + // marking visited/etc. + for (const DefPath &N : const_def_path(R.PrimaryClobber.LastNode)) + cacheDefPath(N, R.PrimaryClobber.Clobber); + return; + } + + // PrimaryClobber is our answer. If we can cache anything back, we need to + // stop caching when we visit PrimaryClobber. + SmallBitVector Visited(Paths.size()); + for (const DefPath &N : const_def_path(R.PrimaryClobber.LastNode)) { + Visited[defPathIndex(N)] = true; + cacheDefPath(N, R.PrimaryClobber.Clobber); + } + + for (const TerminatedPath &P : R.OtherClobbers) { + for (const DefPath &N : const_def_path(P.LastNode)) { + ListIndex NIndex = defPathIndex(N); + if (Visited[NIndex]) + break; + Visited[NIndex] = true; + cacheDefPath(N, P.Clobber); + } + } + } + + void verifyOptResult(const OptznResult &R) const { + assert(all_of(R.OtherClobbers, [&](const TerminatedPath &P) { + return MSSA.dominates(P.Clobber, R.PrimaryClobber.Clobber); + })); + } + + void resetPhiOptznState() { + Paths.clear(); + VisitedPhis.clear(); + } + +public: + ClobberWalker(const MemorySSA &MSSA, AliasAnalysis &AA, DominatorTree &DT, + WalkerCache &WC) + : MSSA(MSSA), AA(AA), DT(DT), WC(WC), UseCache(true) {} + + void reset() { WalkTargetCache.clear(); } + + /// Finds the nearest clobber for the given query, optimizing phis if + /// possible. + MemoryAccess *findClobber(MemoryAccess *Start, UpwardsMemoryQuery &Q, + bool UseWalkerCache = true) { + setUseCache(UseWalkerCache); + Query = &Q; + + MemoryAccess *Current = Start; + // This walker pretends uses don't exist. If we're handed one, silently grab + // its def. (This has the nice side-effect of ensuring we never cache uses) + if (auto *MU = dyn_cast<MemoryUse>(Start)) + Current = MU->getDefiningAccess(); + + DefPath FirstDesc(Q.StartingLoc, Current, Current, None); + // Fast path for the overly-common case (no crazy phi optimization + // necessary) + UpwardsWalkResult WalkResult = walkToPhiOrClobber(FirstDesc); + MemoryAccess *Result; + if (WalkResult.IsKnownClobber) { + cacheDefPath(FirstDesc, WalkResult.Result); + Result = WalkResult.Result; + } else { + OptznResult OptRes = tryOptimizePhi(cast<MemoryPhi>(FirstDesc.Last), + Current, Q.StartingLoc); + verifyOptResult(OptRes); + cacheOptResult(OptRes); + resetPhiOptznState(); + Result = OptRes.PrimaryClobber.Clobber; + } + +#ifdef EXPENSIVE_CHECKS + checkClobberSanity(Current, Result, Q.StartingLoc, MSSA, Q, AA); +#endif + return Result; + } + + void verify(const MemorySSA *MSSA) { assert(MSSA == &this->MSSA); } +}; + +struct RenamePassData { + DomTreeNode *DTN; + DomTreeNode::const_iterator ChildIt; + MemoryAccess *IncomingVal; + + RenamePassData(DomTreeNode *D, DomTreeNode::const_iterator It, + MemoryAccess *M) + : DTN(D), ChildIt(It), IncomingVal(M) {} + void swap(RenamePassData &RHS) { + std::swap(DTN, RHS.DTN); + std::swap(ChildIt, RHS.ChildIt); + std::swap(IncomingVal, RHS.IncomingVal); + } +}; +} // anonymous namespace + +namespace llvm { +/// \brief A MemorySSAWalker that does AA walks and caching of lookups to +/// disambiguate accesses. +/// +/// FIXME: The current implementation of this can take quadratic space in rare +/// cases. This can be fixed, but it is something to note until it is fixed. +/// +/// In order to trigger this behavior, you need to store to N distinct locations +/// (that AA can prove don't alias), perform M stores to other memory +/// locations that AA can prove don't alias any of the initial N locations, and +/// then load from all of the N locations. In this case, we insert M cache +/// entries for each of the N loads. +/// +/// For example: +/// define i32 @foo() { +/// %a = alloca i32, align 4 +/// %b = alloca i32, align 4 +/// store i32 0, i32* %a, align 4 +/// store i32 0, i32* %b, align 4 +/// +/// ; Insert M stores to other memory that doesn't alias %a or %b here +/// +/// %c = load i32, i32* %a, align 4 ; Caches M entries in +/// ; CachedUpwardsClobberingAccess for the +/// ; MemoryLocation %a +/// %d = load i32, i32* %b, align 4 ; Caches M entries in +/// ; CachedUpwardsClobberingAccess for the +/// ; MemoryLocation %b +/// +/// ; For completeness' sake, loading %a or %b again would not cache *another* +/// ; M entries. +/// %r = add i32 %c, %d +/// ret i32 %r +/// } +class MemorySSA::CachingWalker final : public MemorySSAWalker { + WalkerCache Cache; + ClobberWalker Walker; + bool AutoResetWalker; + + MemoryAccess *getClobberingMemoryAccess(MemoryAccess *, UpwardsMemoryQuery &); + void verifyRemoved(MemoryAccess *); + +public: + CachingWalker(MemorySSA *, AliasAnalysis *, DominatorTree *); + ~CachingWalker() override; + + using MemorySSAWalker::getClobberingMemoryAccess; + MemoryAccess *getClobberingMemoryAccess(MemoryAccess *) override; + MemoryAccess *getClobberingMemoryAccess(MemoryAccess *, + const MemoryLocation &) override; + void invalidateInfo(MemoryAccess *) override; + + /// Whether we call resetClobberWalker() after each time we *actually* walk to + /// answer a clobber query. + void setAutoResetWalker(bool AutoReset) { AutoResetWalker = AutoReset; } + + /// Drop the walker's persistent data structures. At the moment, this means + /// "drop the walker's cache of BasicBlocks -> + /// earliest-MemoryAccess-we-can-optimize-to". This is necessary if we're + /// going to have DT updates, if we remove MemoryAccesses, etc. + void resetClobberWalker() { Walker.reset(); } + + void verify(const MemorySSA *MSSA) override { + MemorySSAWalker::verify(MSSA); + Walker.verify(MSSA); + } +}; + +/// \brief Rename a single basic block into MemorySSA form. +/// Uses the standard SSA renaming algorithm. +/// \returns The new incoming value. +MemoryAccess *MemorySSA::renameBlock(BasicBlock *BB, + MemoryAccess *IncomingVal) { + auto It = PerBlockAccesses.find(BB); + // Skip most processing if the list is empty. + if (It != PerBlockAccesses.end()) { + AccessList *Accesses = It->second.get(); + for (MemoryAccess &L : *Accesses) { + if (MemoryUseOrDef *MUD = dyn_cast<MemoryUseOrDef>(&L)) { + if (MUD->getDefiningAccess() == nullptr) + MUD->setDefiningAccess(IncomingVal); + if (isa<MemoryDef>(&L)) + IncomingVal = &L; + } else { + IncomingVal = &L; + } + } + } + + // Pass through values to our successors + for (const BasicBlock *S : successors(BB)) { + auto It = PerBlockAccesses.find(S); + // Rename the phi nodes in our successor block + if (It == PerBlockAccesses.end() || !isa<MemoryPhi>(It->second->front())) + continue; + AccessList *Accesses = It->second.get(); + auto *Phi = cast<MemoryPhi>(&Accesses->front()); + Phi->addIncoming(IncomingVal, BB); + } + + return IncomingVal; +} + +/// \brief This is the standard SSA renaming algorithm. +/// +/// We walk the dominator tree in preorder, renaming accesses, and then filling +/// in phi nodes in our successors. +void MemorySSA::renamePass(DomTreeNode *Root, MemoryAccess *IncomingVal, + SmallPtrSet<BasicBlock *, 16> &Visited) { + SmallVector<RenamePassData, 32> WorkStack; + IncomingVal = renameBlock(Root->getBlock(), IncomingVal); + WorkStack.push_back({Root, Root->begin(), IncomingVal}); + Visited.insert(Root->getBlock()); + + while (!WorkStack.empty()) { + DomTreeNode *Node = WorkStack.back().DTN; + DomTreeNode::const_iterator ChildIt = WorkStack.back().ChildIt; + IncomingVal = WorkStack.back().IncomingVal; + + if (ChildIt == Node->end()) { + WorkStack.pop_back(); + } else { + DomTreeNode *Child = *ChildIt; + ++WorkStack.back().ChildIt; + BasicBlock *BB = Child->getBlock(); + Visited.insert(BB); + IncomingVal = renameBlock(BB, IncomingVal); + WorkStack.push_back({Child, Child->begin(), IncomingVal}); + } + } +} + +/// \brief Compute dominator levels, used by the phi insertion algorithm above. +void MemorySSA::computeDomLevels(DenseMap<DomTreeNode *, unsigned> &DomLevels) { + for (auto DFI = df_begin(DT->getRootNode()), DFE = df_end(DT->getRootNode()); + DFI != DFE; ++DFI) + DomLevels[*DFI] = DFI.getPathLength() - 1; +} + +/// \brief This handles unreachable block accesses by deleting phi nodes in +/// unreachable blocks, and marking all other unreachable MemoryAccess's as +/// being uses of the live on entry definition. +void MemorySSA::markUnreachableAsLiveOnEntry(BasicBlock *BB) { + assert(!DT->isReachableFromEntry(BB) && + "Reachable block found while handling unreachable blocks"); + + // Make sure phi nodes in our reachable successors end up with a + // LiveOnEntryDef for our incoming edge, even though our block is forward + // unreachable. We could just disconnect these blocks from the CFG fully, + // but we do not right now. + for (const BasicBlock *S : successors(BB)) { + if (!DT->isReachableFromEntry(S)) + continue; + auto It = PerBlockAccesses.find(S); + // Rename the phi nodes in our successor block + if (It == PerBlockAccesses.end() || !isa<MemoryPhi>(It->second->front())) + continue; + AccessList *Accesses = It->second.get(); + auto *Phi = cast<MemoryPhi>(&Accesses->front()); + Phi->addIncoming(LiveOnEntryDef.get(), BB); + } + + auto It = PerBlockAccesses.find(BB); + if (It == PerBlockAccesses.end()) + return; + + auto &Accesses = It->second; + for (auto AI = Accesses->begin(), AE = Accesses->end(); AI != AE;) { + auto Next = std::next(AI); + // If we have a phi, just remove it. We are going to replace all + // users with live on entry. + if (auto *UseOrDef = dyn_cast<MemoryUseOrDef>(AI)) + UseOrDef->setDefiningAccess(LiveOnEntryDef.get()); + else + Accesses->erase(AI); + AI = Next; + } +} + +MemorySSA::MemorySSA(Function &Func, AliasAnalysis *AA, DominatorTree *DT) + : AA(AA), DT(DT), F(Func), LiveOnEntryDef(nullptr), Walker(nullptr), + NextID(INVALID_MEMORYACCESS_ID) { + buildMemorySSA(); +} + +MemorySSA::~MemorySSA() { + // Drop all our references + for (const auto &Pair : PerBlockAccesses) + for (MemoryAccess &MA : *Pair.second) + MA.dropAllReferences(); +} + +MemorySSA::AccessList *MemorySSA::getOrCreateAccessList(const BasicBlock *BB) { + auto Res = PerBlockAccesses.insert(std::make_pair(BB, nullptr)); + + if (Res.second) + Res.first->second = make_unique<AccessList>(); + return Res.first->second.get(); +} + +/// This class is a batch walker of all MemoryUse's in the program, and points +/// their defining access at the thing that actually clobbers them. Because it +/// is a batch walker that touches everything, it does not operate like the +/// other walkers. This walker is basically performing a top-down SSA renaming +/// pass, where the version stack is used as the cache. This enables it to be +/// significantly more time and memory efficient than using the regular walker, +/// which is walking bottom-up. +class MemorySSA::OptimizeUses { +public: + OptimizeUses(MemorySSA *MSSA, MemorySSAWalker *Walker, AliasAnalysis *AA, + DominatorTree *DT) + : MSSA(MSSA), Walker(Walker), AA(AA), DT(DT) { + Walker = MSSA->getWalker(); + } + + void optimizeUses(); + +private: + /// This represents where a given memorylocation is in the stack. + struct MemlocStackInfo { + // This essentially is keeping track of versions of the stack. Whenever + // the stack changes due to pushes or pops, these versions increase. + unsigned long StackEpoch; + unsigned long PopEpoch; + // This is the lower bound of places on the stack to check. It is equal to + // the place the last stack walk ended. + // Note: Correctness depends on this being initialized to 0, which densemap + // does + unsigned long LowerBound; + const BasicBlock *LowerBoundBlock; + // This is where the last walk for this memory location ended. + unsigned long LastKill; + bool LastKillValid; + }; + void optimizeUsesInBlock(const BasicBlock *, unsigned long &, unsigned long &, + SmallVectorImpl<MemoryAccess *> &, + DenseMap<MemoryLocOrCall, MemlocStackInfo> &); + MemorySSA *MSSA; + MemorySSAWalker *Walker; + AliasAnalysis *AA; + DominatorTree *DT; +}; + +/// Optimize the uses in a given block This is basically the SSA renaming +/// algorithm, with one caveat: We are able to use a single stack for all +/// MemoryUses. This is because the set of *possible* reaching MemoryDefs is +/// the same for every MemoryUse. The *actual* clobbering MemoryDef is just +/// going to be some position in that stack of possible ones. +/// +/// We track the stack positions that each MemoryLocation needs +/// to check, and last ended at. This is because we only want to check the +/// things that changed since last time. The same MemoryLocation should +/// get clobbered by the same store (getModRefInfo does not use invariantness or +/// things like this, and if they start, we can modify MemoryLocOrCall to +/// include relevant data) +void MemorySSA::OptimizeUses::optimizeUsesInBlock( + const BasicBlock *BB, unsigned long &StackEpoch, unsigned long &PopEpoch, + SmallVectorImpl<MemoryAccess *> &VersionStack, + DenseMap<MemoryLocOrCall, MemlocStackInfo> &LocStackInfo) { + + /// If no accesses, nothing to do. + MemorySSA::AccessList *Accesses = MSSA->getWritableBlockAccesses(BB); + if (Accesses == nullptr) + return; + + // Pop everything that doesn't dominate the current block off the stack, + // increment the PopEpoch to account for this. + while (!VersionStack.empty()) { + BasicBlock *BackBlock = VersionStack.back()->getBlock(); + if (DT->dominates(BackBlock, BB)) + break; + while (VersionStack.back()->getBlock() == BackBlock) + VersionStack.pop_back(); + ++PopEpoch; + } + for (MemoryAccess &MA : *Accesses) { + auto *MU = dyn_cast<MemoryUse>(&MA); + if (!MU) { + VersionStack.push_back(&MA); + ++StackEpoch; + continue; + } + + if (isUseTriviallyOptimizableToLiveOnEntry(*AA, MU->getMemoryInst())) { + MU->setDefiningAccess(MSSA->getLiveOnEntryDef(), true); + continue; + } + + MemoryLocOrCall UseMLOC(MU); + auto &LocInfo = LocStackInfo[UseMLOC]; + // If the pop epoch changed, it means we've removed stuff from top of + // stack due to changing blocks. We may have to reset the lower bound or + // last kill info. + if (LocInfo.PopEpoch != PopEpoch) { + LocInfo.PopEpoch = PopEpoch; + LocInfo.StackEpoch = StackEpoch; + // If the lower bound was in something that no longer dominates us, we + // have to reset it. + // We can't simply track stack size, because the stack may have had + // pushes/pops in the meantime. + // XXX: This is non-optimal, but only is slower cases with heavily + // branching dominator trees. To get the optimal number of queries would + // be to make lowerbound and lastkill a per-loc stack, and pop it until + // the top of that stack dominates us. This does not seem worth it ATM. + // A much cheaper optimization would be to always explore the deepest + // branch of the dominator tree first. This will guarantee this resets on + // the smallest set of blocks. + if (LocInfo.LowerBoundBlock && LocInfo.LowerBoundBlock != BB && + !DT->dominates(LocInfo.LowerBoundBlock, BB)) { + // Reset the lower bound of things to check. + // TODO: Some day we should be able to reset to last kill, rather than + // 0. + LocInfo.LowerBound = 0; + LocInfo.LowerBoundBlock = VersionStack[0]->getBlock(); + LocInfo.LastKillValid = false; + } + } else if (LocInfo.StackEpoch != StackEpoch) { + // If all that has changed is the StackEpoch, we only have to check the + // new things on the stack, because we've checked everything before. In + // this case, the lower bound of things to check remains the same. + LocInfo.PopEpoch = PopEpoch; + LocInfo.StackEpoch = StackEpoch; + } + if (!LocInfo.LastKillValid) { + LocInfo.LastKill = VersionStack.size() - 1; + LocInfo.LastKillValid = true; + } + + // At this point, we should have corrected last kill and LowerBound to be + // in bounds. + assert(LocInfo.LowerBound < VersionStack.size() && + "Lower bound out of range"); + assert(LocInfo.LastKill < VersionStack.size() && + "Last kill info out of range"); + // In any case, the new upper bound is the top of the stack. + unsigned long UpperBound = VersionStack.size() - 1; + + if (UpperBound - LocInfo.LowerBound > MaxCheckLimit) { + DEBUG(dbgs() << "MemorySSA skipping optimization of " << *MU << " (" + << *(MU->getMemoryInst()) << ")" + << " because there are " << UpperBound - LocInfo.LowerBound + << " stores to disambiguate\n"); + // Because we did not walk, LastKill is no longer valid, as this may + // have been a kill. + LocInfo.LastKillValid = false; + continue; + } + bool FoundClobberResult = false; + while (UpperBound > LocInfo.LowerBound) { + if (isa<MemoryPhi>(VersionStack[UpperBound])) { + // For phis, use the walker, see where we ended up, go there + Instruction *UseInst = MU->getMemoryInst(); + MemoryAccess *Result = Walker->getClobberingMemoryAccess(UseInst); + // We are guaranteed to find it or something is wrong + while (VersionStack[UpperBound] != Result) { + assert(UpperBound != 0); + --UpperBound; + } + FoundClobberResult = true; + break; + } + + MemoryDef *MD = cast<MemoryDef>(VersionStack[UpperBound]); + // If the lifetime of the pointer ends at this instruction, it's live on + // entry. + if (!UseMLOC.IsCall && lifetimeEndsAt(MD, UseMLOC.getLoc(), *AA)) { + // Reset UpperBound to liveOnEntryDef's place in the stack + UpperBound = 0; + FoundClobberResult = true; + break; + } + if (instructionClobbersQuery(MD, MU, UseMLOC, *AA)) { + FoundClobberResult = true; + break; + } + --UpperBound; + } + // At the end of this loop, UpperBound is either a clobber, or lower bound + // PHI walking may cause it to be < LowerBound, and in fact, < LastKill. + if (FoundClobberResult || UpperBound < LocInfo.LastKill) { + MU->setDefiningAccess(VersionStack[UpperBound], true); + // We were last killed now by where we got to + LocInfo.LastKill = UpperBound; + } else { + // Otherwise, we checked all the new ones, and now we know we can get to + // LastKill. + MU->setDefiningAccess(VersionStack[LocInfo.LastKill], true); + } + LocInfo.LowerBound = VersionStack.size() - 1; + LocInfo.LowerBoundBlock = BB; + } +} + +/// Optimize uses to point to their actual clobbering definitions. +void MemorySSA::OptimizeUses::optimizeUses() { + + // We perform a non-recursive top-down dominator tree walk + struct StackInfo { + const DomTreeNode *Node; + DomTreeNode::const_iterator Iter; + }; + + SmallVector<MemoryAccess *, 16> VersionStack; + SmallVector<StackInfo, 16> DomTreeWorklist; + DenseMap<MemoryLocOrCall, MemlocStackInfo> LocStackInfo; + VersionStack.push_back(MSSA->getLiveOnEntryDef()); + + unsigned long StackEpoch = 1; + unsigned long PopEpoch = 1; + for (const auto *DomNode : depth_first(DT->getRootNode())) + optimizeUsesInBlock(DomNode->getBlock(), StackEpoch, PopEpoch, VersionStack, + LocStackInfo); +} + +void MemorySSA::placePHINodes( + const SmallPtrSetImpl<BasicBlock *> &DefiningBlocks, + const DenseMap<const BasicBlock *, unsigned int> &BBNumbers) { + // Determine where our MemoryPhi's should go + ForwardIDFCalculator IDFs(*DT); + IDFs.setDefiningBlocks(DefiningBlocks); + SmallVector<BasicBlock *, 32> IDFBlocks; + IDFs.calculate(IDFBlocks); + + std::sort(IDFBlocks.begin(), IDFBlocks.end(), + [&BBNumbers](const BasicBlock *A, const BasicBlock *B) { + return BBNumbers.lookup(A) < BBNumbers.lookup(B); + }); + + // Now place MemoryPhi nodes. + for (auto &BB : IDFBlocks) { + // Insert phi node + AccessList *Accesses = getOrCreateAccessList(BB); + MemoryPhi *Phi = new MemoryPhi(BB->getContext(), BB, NextID++); + ValueToMemoryAccess[BB] = Phi; + // Phi's always are placed at the front of the block. + Accesses->push_front(Phi); + } +} + +void MemorySSA::buildMemorySSA() { + // We create an access to represent "live on entry", for things like + // arguments or users of globals, where the memory they use is defined before + // the beginning of the function. We do not actually insert it into the IR. + // We do not define a live on exit for the immediate uses, and thus our + // semantics do *not* imply that something with no immediate uses can simply + // be removed. + BasicBlock &StartingPoint = F.getEntryBlock(); + LiveOnEntryDef = make_unique<MemoryDef>(F.getContext(), nullptr, nullptr, + &StartingPoint, NextID++); + DenseMap<const BasicBlock *, unsigned int> BBNumbers; + unsigned NextBBNum = 0; + + // We maintain lists of memory accesses per-block, trading memory for time. We + // could just look up the memory access for every possible instruction in the + // stream. + SmallPtrSet<BasicBlock *, 32> DefiningBlocks; + SmallPtrSet<BasicBlock *, 32> DefUseBlocks; + // Go through each block, figure out where defs occur, and chain together all + // the accesses. + for (BasicBlock &B : F) { + BBNumbers[&B] = NextBBNum++; + bool InsertIntoDef = false; + AccessList *Accesses = nullptr; + for (Instruction &I : B) { + MemoryUseOrDef *MUD = createNewAccess(&I); + if (!MUD) + continue; + InsertIntoDef |= isa<MemoryDef>(MUD); + + if (!Accesses) + Accesses = getOrCreateAccessList(&B); + Accesses->push_back(MUD); + } + if (InsertIntoDef) + DefiningBlocks.insert(&B); + if (Accesses) + DefUseBlocks.insert(&B); + } + placePHINodes(DefiningBlocks, BBNumbers); + + // Now do regular SSA renaming on the MemoryDef/MemoryUse. Visited will get + // filled in with all blocks. + SmallPtrSet<BasicBlock *, 16> Visited; + renamePass(DT->getRootNode(), LiveOnEntryDef.get(), Visited); + + CachingWalker *Walker = getWalkerImpl(); + + // We're doing a batch of updates; don't drop useful caches between them. + Walker->setAutoResetWalker(false); + OptimizeUses(this, Walker, AA, DT).optimizeUses(); + Walker->setAutoResetWalker(true); + Walker->resetClobberWalker(); + + // Mark the uses in unreachable blocks as live on entry, so that they go + // somewhere. + for (auto &BB : F) + if (!Visited.count(&BB)) + markUnreachableAsLiveOnEntry(&BB); +} + +MemorySSAWalker *MemorySSA::getWalker() { return getWalkerImpl(); } + +MemorySSA::CachingWalker *MemorySSA::getWalkerImpl() { + if (Walker) + return Walker.get(); + + Walker = make_unique<CachingWalker>(this, AA, DT); + return Walker.get(); +} + +MemoryPhi *MemorySSA::createMemoryPhi(BasicBlock *BB) { + assert(!getMemoryAccess(BB) && "MemoryPhi already exists for this BB"); + AccessList *Accesses = getOrCreateAccessList(BB); + MemoryPhi *Phi = new MemoryPhi(BB->getContext(), BB, NextID++); + ValueToMemoryAccess[BB] = Phi; + // Phi's always are placed at the front of the block. + Accesses->push_front(Phi); + BlockNumberingValid.erase(BB); + return Phi; +} + +MemoryUseOrDef *MemorySSA::createDefinedAccess(Instruction *I, + MemoryAccess *Definition) { + assert(!isa<PHINode>(I) && "Cannot create a defined access for a PHI"); + MemoryUseOrDef *NewAccess = createNewAccess(I); + assert( + NewAccess != nullptr && + "Tried to create a memory access for a non-memory touching instruction"); + NewAccess->setDefiningAccess(Definition); + return NewAccess; +} + +MemoryAccess *MemorySSA::createMemoryAccessInBB(Instruction *I, + MemoryAccess *Definition, + const BasicBlock *BB, + InsertionPlace Point) { + MemoryUseOrDef *NewAccess = createDefinedAccess(I, Definition); + auto *Accesses = getOrCreateAccessList(BB); + if (Point == Beginning) { + // It goes after any phi nodes + auto AI = find_if( + *Accesses, [](const MemoryAccess &MA) { return !isa<MemoryPhi>(MA); }); + + Accesses->insert(AI, NewAccess); + } else { + Accesses->push_back(NewAccess); + } + BlockNumberingValid.erase(BB); + return NewAccess; +} + +MemoryUseOrDef *MemorySSA::createMemoryAccessBefore(Instruction *I, + MemoryAccess *Definition, + MemoryUseOrDef *InsertPt) { + assert(I->getParent() == InsertPt->getBlock() && + "New and old access must be in the same block"); + MemoryUseOrDef *NewAccess = createDefinedAccess(I, Definition); + auto *Accesses = getOrCreateAccessList(InsertPt->getBlock()); + Accesses->insert(AccessList::iterator(InsertPt), NewAccess); + BlockNumberingValid.erase(InsertPt->getBlock()); + return NewAccess; +} + +MemoryUseOrDef *MemorySSA::createMemoryAccessAfter(Instruction *I, + MemoryAccess *Definition, + MemoryAccess *InsertPt) { + assert(I->getParent() == InsertPt->getBlock() && + "New and old access must be in the same block"); + MemoryUseOrDef *NewAccess = createDefinedAccess(I, Definition); + auto *Accesses = getOrCreateAccessList(InsertPt->getBlock()); + Accesses->insertAfter(AccessList::iterator(InsertPt), NewAccess); + BlockNumberingValid.erase(InsertPt->getBlock()); + return NewAccess; +} + +void MemorySSA::spliceMemoryAccessAbove(MemoryDef *Where, + MemoryUseOrDef *What) { + assert(What != getLiveOnEntryDef() && + Where != getLiveOnEntryDef() && "Can't splice (above) LOE."); + assert(dominates(Where, What) && "Only upwards splices are permitted."); + + if (Where == What) + return; + if (isa<MemoryDef>(What)) { + // TODO: possibly use removeMemoryAccess' more efficient RAUW + What->replaceAllUsesWith(What->getDefiningAccess()); + What->setDefiningAccess(Where->getDefiningAccess()); + Where->setDefiningAccess(What); + } + AccessList *Src = getWritableBlockAccesses(What->getBlock()); + AccessList *Dest = getWritableBlockAccesses(Where->getBlock()); + Dest->splice(AccessList::iterator(Where), *Src, What); + + BlockNumberingValid.erase(What->getBlock()); + if (What->getBlock() != Where->getBlock()) + BlockNumberingValid.erase(Where->getBlock()); +} + +/// \brief Helper function to create new memory accesses +MemoryUseOrDef *MemorySSA::createNewAccess(Instruction *I) { + // The assume intrinsic has a control dependency which we model by claiming + // that it writes arbitrarily. Ignore that fake memory dependency here. + // FIXME: Replace this special casing with a more accurate modelling of + // assume's control dependency. + if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) + if (II->getIntrinsicID() == Intrinsic::assume) + return nullptr; + + // Find out what affect this instruction has on memory. + ModRefInfo ModRef = AA->getModRefInfo(I); + bool Def = bool(ModRef & MRI_Mod); + bool Use = bool(ModRef & MRI_Ref); + + // It's possible for an instruction to not modify memory at all. During + // construction, we ignore them. + if (!Def && !Use) + return nullptr; + + assert((Def || Use) && + "Trying to create a memory access with a non-memory instruction"); + + MemoryUseOrDef *MUD; + if (Def) + MUD = new MemoryDef(I->getContext(), nullptr, I, I->getParent(), NextID++); + else + MUD = new MemoryUse(I->getContext(), nullptr, I, I->getParent()); + ValueToMemoryAccess[I] = MUD; + return MUD; +} + +MemoryAccess *MemorySSA::findDominatingDef(BasicBlock *UseBlock, + enum InsertionPlace Where) { + // Handle the initial case + if (Where == Beginning) + // The only thing that could define us at the beginning is a phi node + if (MemoryPhi *Phi = getMemoryAccess(UseBlock)) + return Phi; + + DomTreeNode *CurrNode = DT->getNode(UseBlock); + // Need to be defined by our dominator + if (Where == Beginning) + CurrNode = CurrNode->getIDom(); + Where = End; + while (CurrNode) { + auto It = PerBlockAccesses.find(CurrNode->getBlock()); + if (It != PerBlockAccesses.end()) { + auto &Accesses = It->second; + for (MemoryAccess &RA : reverse(*Accesses)) { + if (isa<MemoryDef>(RA) || isa<MemoryPhi>(RA)) + return &RA; + } + } + CurrNode = CurrNode->getIDom(); + } + return LiveOnEntryDef.get(); +} + +/// \brief Returns true if \p Replacer dominates \p Replacee . +bool MemorySSA::dominatesUse(const MemoryAccess *Replacer, + const MemoryAccess *Replacee) const { + if (isa<MemoryUseOrDef>(Replacee)) + return DT->dominates(Replacer->getBlock(), Replacee->getBlock()); + const auto *MP = cast<MemoryPhi>(Replacee); + // For a phi node, the use occurs in the predecessor block of the phi node. + // Since we may occur multiple times in the phi node, we have to check each + // operand to ensure Replacer dominates each operand where Replacee occurs. + for (const Use &Arg : MP->operands()) { + if (Arg.get() != Replacee && + !DT->dominates(Replacer->getBlock(), MP->getIncomingBlock(Arg))) + return false; + } + return true; +} + +/// \brief If all arguments of a MemoryPHI are defined by the same incoming +/// argument, return that argument. +static MemoryAccess *onlySingleValue(MemoryPhi *MP) { + MemoryAccess *MA = nullptr; + + for (auto &Arg : MP->operands()) { + if (!MA) + MA = cast<MemoryAccess>(Arg); + else if (MA != Arg) + return nullptr; + } + return MA; +} + +/// \brief Properly remove \p MA from all of MemorySSA's lookup tables. +/// +/// Because of the way the intrusive list and use lists work, it is important to +/// do removal in the right order. +void MemorySSA::removeFromLookups(MemoryAccess *MA) { + assert(MA->use_empty() && + "Trying to remove memory access that still has uses"); + BlockNumbering.erase(MA); + if (MemoryUseOrDef *MUD = dyn_cast<MemoryUseOrDef>(MA)) + MUD->setDefiningAccess(nullptr); + // Invalidate our walker's cache if necessary + if (!isa<MemoryUse>(MA)) + Walker->invalidateInfo(MA); + // The call below to erase will destroy MA, so we can't change the order we + // are doing things here + Value *MemoryInst; + if (MemoryUseOrDef *MUD = dyn_cast<MemoryUseOrDef>(MA)) { + MemoryInst = MUD->getMemoryInst(); + } else { + MemoryInst = MA->getBlock(); + } + auto VMA = ValueToMemoryAccess.find(MemoryInst); + if (VMA->second == MA) + ValueToMemoryAccess.erase(VMA); + + auto AccessIt = PerBlockAccesses.find(MA->getBlock()); + std::unique_ptr<AccessList> &Accesses = AccessIt->second; + Accesses->erase(MA); + if (Accesses->empty()) + PerBlockAccesses.erase(AccessIt); +} + +void MemorySSA::removeMemoryAccess(MemoryAccess *MA) { + assert(!isLiveOnEntryDef(MA) && "Trying to remove the live on entry def"); + // We can only delete phi nodes if they have no uses, or we can replace all + // uses with a single definition. + MemoryAccess *NewDefTarget = nullptr; + if (MemoryPhi *MP = dyn_cast<MemoryPhi>(MA)) { + // Note that it is sufficient to know that all edges of the phi node have + // the same argument. If they do, by the definition of dominance frontiers + // (which we used to place this phi), that argument must dominate this phi, + // and thus, must dominate the phi's uses, and so we will not hit the assert + // below. + NewDefTarget = onlySingleValue(MP); + assert((NewDefTarget || MP->use_empty()) && + "We can't delete this memory phi"); + } else { + NewDefTarget = cast<MemoryUseOrDef>(MA)->getDefiningAccess(); + } + + // Re-point the uses at our defining access + if (!MA->use_empty()) { + // Reset optimized on users of this store, and reset the uses. + // A few notes: + // 1. This is a slightly modified version of RAUW to avoid walking the + // uses twice here. + // 2. If we wanted to be complete, we would have to reset the optimized + // flags on users of phi nodes if doing the below makes a phi node have all + // the same arguments. Instead, we prefer users to removeMemoryAccess those + // phi nodes, because doing it here would be N^3. + if (MA->hasValueHandle()) + ValueHandleBase::ValueIsRAUWd(MA, NewDefTarget); + // Note: We assume MemorySSA is not used in metadata since it's not really + // part of the IR. + + while (!MA->use_empty()) { + Use &U = *MA->use_begin(); + if (MemoryUse *MU = dyn_cast<MemoryUse>(U.getUser())) + MU->resetOptimized(); + U.set(NewDefTarget); + } + } + + // The call below to erase will destroy MA, so we can't change the order we + // are doing things here + removeFromLookups(MA); +} + +void MemorySSA::print(raw_ostream &OS) const { + MemorySSAAnnotatedWriter Writer(this); + F.print(OS, &Writer); +} + +void MemorySSA::dump() const { + MemorySSAAnnotatedWriter Writer(this); + F.print(dbgs(), &Writer); +} + +void MemorySSA::verifyMemorySSA() const { + verifyDefUses(F); + verifyDomination(F); + verifyOrdering(F); + Walker->verify(this); +} + +/// \brief Verify that the order and existence of MemoryAccesses matches the +/// order and existence of memory affecting instructions. +void MemorySSA::verifyOrdering(Function &F) const { + // Walk all the blocks, comparing what the lookups think and what the access + // lists think, as well as the order in the blocks vs the order in the access + // lists. + SmallVector<MemoryAccess *, 32> ActualAccesses; + for (BasicBlock &B : F) { + const AccessList *AL = getBlockAccesses(&B); + MemoryAccess *Phi = getMemoryAccess(&B); + if (Phi) + ActualAccesses.push_back(Phi); + for (Instruction &I : B) { + MemoryAccess *MA = getMemoryAccess(&I); + assert((!MA || AL) && "We have memory affecting instructions " + "in this block but they are not in the " + "access list"); + if (MA) + ActualAccesses.push_back(MA); + } + // Either we hit the assert, really have no accesses, or we have both + // accesses and an access list + if (!AL) + continue; + assert(AL->size() == ActualAccesses.size() && + "We don't have the same number of accesses in the block as on the " + "access list"); + auto ALI = AL->begin(); + auto AAI = ActualAccesses.begin(); + while (ALI != AL->end() && AAI != ActualAccesses.end()) { + assert(&*ALI == *AAI && "Not the same accesses in the same order"); + ++ALI; + ++AAI; + } + ActualAccesses.clear(); + } +} + +/// \brief Verify the domination properties of MemorySSA by checking that each +/// definition dominates all of its uses. +void MemorySSA::verifyDomination(Function &F) const { +#ifndef NDEBUG + for (BasicBlock &B : F) { + // Phi nodes are attached to basic blocks + if (MemoryPhi *MP = getMemoryAccess(&B)) + for (const Use &U : MP->uses()) + assert(dominates(MP, U) && "Memory PHI does not dominate it's uses"); + + for (Instruction &I : B) { + MemoryAccess *MD = dyn_cast_or_null<MemoryDef>(getMemoryAccess(&I)); + if (!MD) + continue; + + for (const Use &U : MD->uses()) + assert(dominates(MD, U) && "Memory Def does not dominate it's uses"); + } + } +#endif +} + +/// \brief Verify the def-use lists in MemorySSA, by verifying that \p Use +/// appears in the use list of \p Def. + +void MemorySSA::verifyUseInDefs(MemoryAccess *Def, MemoryAccess *Use) const { +#ifndef NDEBUG + // The live on entry use may cause us to get a NULL def here + if (!Def) + assert(isLiveOnEntryDef(Use) && + "Null def but use not point to live on entry def"); + else + assert(is_contained(Def->users(), Use) && + "Did not find use in def's use list"); +#endif +} + +/// \brief Verify the immediate use information, by walking all the memory +/// accesses and verifying that, for each use, it appears in the +/// appropriate def's use list +void MemorySSA::verifyDefUses(Function &F) const { + for (BasicBlock &B : F) { + // Phi nodes are attached to basic blocks + if (MemoryPhi *Phi = getMemoryAccess(&B)) { + assert(Phi->getNumOperands() == static_cast<unsigned>(std::distance( + pred_begin(&B), pred_end(&B))) && + "Incomplete MemoryPhi Node"); + for (unsigned I = 0, E = Phi->getNumIncomingValues(); I != E; ++I) + verifyUseInDefs(Phi->getIncomingValue(I), Phi); + } + + for (Instruction &I : B) { + if (MemoryUseOrDef *MA = getMemoryAccess(&I)) { + verifyUseInDefs(MA->getDefiningAccess(), MA); + } + } + } +} + +MemoryUseOrDef *MemorySSA::getMemoryAccess(const Instruction *I) const { + return cast_or_null<MemoryUseOrDef>(ValueToMemoryAccess.lookup(I)); +} + +MemoryPhi *MemorySSA::getMemoryAccess(const BasicBlock *BB) const { + return cast_or_null<MemoryPhi>(ValueToMemoryAccess.lookup(cast<Value>(BB))); +} + +/// Perform a local numbering on blocks so that instruction ordering can be +/// determined in constant time. +/// TODO: We currently just number in order. If we numbered by N, we could +/// allow at least N-1 sequences of insertBefore or insertAfter (and at least +/// log2(N) sequences of mixed before and after) without needing to invalidate +/// the numbering. +void MemorySSA::renumberBlock(const BasicBlock *B) const { + // The pre-increment ensures the numbers really start at 1. + unsigned long CurrentNumber = 0; + const AccessList *AL = getBlockAccesses(B); + assert(AL != nullptr && "Asking to renumber an empty block"); + for (const auto &I : *AL) + BlockNumbering[&I] = ++CurrentNumber; + BlockNumberingValid.insert(B); +} + +/// \brief Determine, for two memory accesses in the same block, +/// whether \p Dominator dominates \p Dominatee. +/// \returns True if \p Dominator dominates \p Dominatee. +bool MemorySSA::locallyDominates(const MemoryAccess *Dominator, + const MemoryAccess *Dominatee) const { + + const BasicBlock *DominatorBlock = Dominator->getBlock(); + + assert((DominatorBlock == Dominatee->getBlock()) && + "Asking for local domination when accesses are in different blocks!"); + // A node dominates itself. + if (Dominatee == Dominator) + return true; + + // When Dominatee is defined on function entry, it is not dominated by another + // memory access. + if (isLiveOnEntryDef(Dominatee)) + return false; + + // When Dominator is defined on function entry, it dominates the other memory + // access. + if (isLiveOnEntryDef(Dominator)) + return true; + + if (!BlockNumberingValid.count(DominatorBlock)) + renumberBlock(DominatorBlock); + + unsigned long DominatorNum = BlockNumbering.lookup(Dominator); + // All numbers start with 1 + assert(DominatorNum != 0 && "Block was not numbered properly"); + unsigned long DominateeNum = BlockNumbering.lookup(Dominatee); + assert(DominateeNum != 0 && "Block was not numbered properly"); + return DominatorNum < DominateeNum; +} + +bool MemorySSA::dominates(const MemoryAccess *Dominator, + const MemoryAccess *Dominatee) const { + if (Dominator == Dominatee) + return true; + + if (isLiveOnEntryDef(Dominatee)) + return false; + + if (Dominator->getBlock() != Dominatee->getBlock()) + return DT->dominates(Dominator->getBlock(), Dominatee->getBlock()); + return locallyDominates(Dominator, Dominatee); +} + +bool MemorySSA::dominates(const MemoryAccess *Dominator, + const Use &Dominatee) const { + if (MemoryPhi *MP = dyn_cast<MemoryPhi>(Dominatee.getUser())) { + BasicBlock *UseBB = MP->getIncomingBlock(Dominatee); + // The def must dominate the incoming block of the phi. + if (UseBB != Dominator->getBlock()) + return DT->dominates(Dominator->getBlock(), UseBB); + // If the UseBB and the DefBB are the same, compare locally. + return locallyDominates(Dominator, cast<MemoryAccess>(Dominatee)); + } + // If it's not a PHI node use, the normal dominates can already handle it. + return dominates(Dominator, cast<MemoryAccess>(Dominatee.getUser())); +} + +const static char LiveOnEntryStr[] = "liveOnEntry"; + +void MemoryDef::print(raw_ostream &OS) const { + MemoryAccess *UO = getDefiningAccess(); + + OS << getID() << " = MemoryDef("; + if (UO && UO->getID()) + OS << UO->getID(); + else + OS << LiveOnEntryStr; + OS << ')'; +} + +void MemoryPhi::print(raw_ostream &OS) const { + bool First = true; + OS << getID() << " = MemoryPhi("; + for (const auto &Op : operands()) { + BasicBlock *BB = getIncomingBlock(Op); + MemoryAccess *MA = cast<MemoryAccess>(Op); + if (!First) + OS << ','; + else + First = false; + + OS << '{'; + if (BB->hasName()) + OS << BB->getName(); + else + BB->printAsOperand(OS, false); + OS << ','; + if (unsigned ID = MA->getID()) + OS << ID; + else + OS << LiveOnEntryStr; + OS << '}'; + } + OS << ')'; +} + +MemoryAccess::~MemoryAccess() {} + +void MemoryUse::print(raw_ostream &OS) const { + MemoryAccess *UO = getDefiningAccess(); + OS << "MemoryUse("; + if (UO && UO->getID()) + OS << UO->getID(); + else + OS << LiveOnEntryStr; + OS << ')'; +} + +void MemoryAccess::dump() const { + print(dbgs()); + dbgs() << "\n"; +} + +char MemorySSAPrinterLegacyPass::ID = 0; + +MemorySSAPrinterLegacyPass::MemorySSAPrinterLegacyPass() : FunctionPass(ID) { + initializeMemorySSAPrinterLegacyPassPass(*PassRegistry::getPassRegistry()); +} + +void MemorySSAPrinterLegacyPass::getAnalysisUsage(AnalysisUsage &AU) const { + AU.setPreservesAll(); + AU.addRequired<MemorySSAWrapperPass>(); + AU.addPreserved<MemorySSAWrapperPass>(); +} + +bool MemorySSAPrinterLegacyPass::runOnFunction(Function &F) { + auto &MSSA = getAnalysis<MemorySSAWrapperPass>().getMSSA(); + MSSA.print(dbgs()); + if (VerifyMemorySSA) + MSSA.verifyMemorySSA(); + return false; +} + +AnalysisKey MemorySSAAnalysis::Key; + +MemorySSAAnalysis::Result MemorySSAAnalysis::run(Function &F, + FunctionAnalysisManager &AM) { + auto &DT = AM.getResult<DominatorTreeAnalysis>(F); + auto &AA = AM.getResult<AAManager>(F); + return MemorySSAAnalysis::Result(make_unique<MemorySSA>(F, &AA, &DT)); +} + +PreservedAnalyses MemorySSAPrinterPass::run(Function &F, + FunctionAnalysisManager &AM) { + OS << "MemorySSA for function: " << F.getName() << "\n"; + AM.getResult<MemorySSAAnalysis>(F).getMSSA().print(OS); + + return PreservedAnalyses::all(); +} + +PreservedAnalyses MemorySSAVerifierPass::run(Function &F, + FunctionAnalysisManager &AM) { + AM.getResult<MemorySSAAnalysis>(F).getMSSA().verifyMemorySSA(); + + return PreservedAnalyses::all(); +} + +char MemorySSAWrapperPass::ID = 0; + +MemorySSAWrapperPass::MemorySSAWrapperPass() : FunctionPass(ID) { + initializeMemorySSAWrapperPassPass(*PassRegistry::getPassRegistry()); +} + +void MemorySSAWrapperPass::releaseMemory() { MSSA.reset(); } + +void MemorySSAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const { + AU.setPreservesAll(); + AU.addRequiredTransitive<DominatorTreeWrapperPass>(); + AU.addRequiredTransitive<AAResultsWrapperPass>(); +} + +bool MemorySSAWrapperPass::runOnFunction(Function &F) { + auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); + auto &AA = getAnalysis<AAResultsWrapperPass>().getAAResults(); + MSSA.reset(new MemorySSA(F, &AA, &DT)); + return false; +} + +void MemorySSAWrapperPass::verifyAnalysis() const { MSSA->verifyMemorySSA(); } + +void MemorySSAWrapperPass::print(raw_ostream &OS, const Module *M) const { + MSSA->print(OS); +} + +MemorySSAWalker::MemorySSAWalker(MemorySSA *M) : MSSA(M) {} + +MemorySSA::CachingWalker::CachingWalker(MemorySSA *M, AliasAnalysis *A, + DominatorTree *D) + : MemorySSAWalker(M), Walker(*M, *A, *D, Cache), AutoResetWalker(true) {} + +MemorySSA::CachingWalker::~CachingWalker() {} + +void MemorySSA::CachingWalker::invalidateInfo(MemoryAccess *MA) { + // TODO: We can do much better cache invalidation with differently stored + // caches. For now, for MemoryUses, we simply remove them + // from the cache, and kill the entire call/non-call cache for everything + // else. The problem is for phis or defs, currently we'd need to follow use + // chains down and invalidate anything below us in the chain that currently + // terminates at this access. + + // See if this is a MemoryUse, if so, just remove the cached info. MemoryUse + // is by definition never a barrier, so nothing in the cache could point to + // this use. In that case, we only need invalidate the info for the use + // itself. + + if (MemoryUse *MU = dyn_cast<MemoryUse>(MA)) { + UpwardsMemoryQuery Q(MU->getMemoryInst(), MU); + Cache.remove(MU, Q.StartingLoc, Q.IsCall); + MU->resetOptimized(); + } else { + // If it is not a use, the best we can do right now is destroy the cache. + Cache.clear(); + } + +#ifdef EXPENSIVE_CHECKS + verifyRemoved(MA); +#endif +} + +/// \brief Walk the use-def chains starting at \p MA and find +/// the MemoryAccess that actually clobbers Loc. +/// +/// \returns our clobbering memory access +MemoryAccess *MemorySSA::CachingWalker::getClobberingMemoryAccess( + MemoryAccess *StartingAccess, UpwardsMemoryQuery &Q) { + MemoryAccess *New = Walker.findClobber(StartingAccess, Q); +#ifdef EXPENSIVE_CHECKS + MemoryAccess *NewNoCache = + Walker.findClobber(StartingAccess, Q, /*UseWalkerCache=*/false); + assert(NewNoCache == New && "Cache made us hand back a different result?"); +#endif + if (AutoResetWalker) + resetClobberWalker(); + return New; +} + +MemoryAccess *MemorySSA::CachingWalker::getClobberingMemoryAccess( + MemoryAccess *StartingAccess, const MemoryLocation &Loc) { + if (isa<MemoryPhi>(StartingAccess)) + return StartingAccess; + + auto *StartingUseOrDef = cast<MemoryUseOrDef>(StartingAccess); + if (MSSA->isLiveOnEntryDef(StartingUseOrDef)) + return StartingUseOrDef; + + Instruction *I = StartingUseOrDef->getMemoryInst(); + + // Conservatively, fences are always clobbers, so don't perform the walk if we + // hit a fence. + if (!ImmutableCallSite(I) && I->isFenceLike()) + return StartingUseOrDef; + + UpwardsMemoryQuery Q; + Q.OriginalAccess = StartingUseOrDef; + Q.StartingLoc = Loc; + Q.Inst = I; + Q.IsCall = false; + + if (auto *CacheResult = Cache.lookup(StartingUseOrDef, Loc, Q.IsCall)) + return CacheResult; + + // Unlike the other function, do not walk to the def of a def, because we are + // handed something we already believe is the clobbering access. + MemoryAccess *DefiningAccess = isa<MemoryUse>(StartingUseOrDef) + ? StartingUseOrDef->getDefiningAccess() + : StartingUseOrDef; + + MemoryAccess *Clobber = getClobberingMemoryAccess(DefiningAccess, Q); + DEBUG(dbgs() << "Starting Memory SSA clobber for " << *I << " is "); + DEBUG(dbgs() << *StartingUseOrDef << "\n"); + DEBUG(dbgs() << "Final Memory SSA clobber for " << *I << " is "); + DEBUG(dbgs() << *Clobber << "\n"); + return Clobber; +} + +MemoryAccess * +MemorySSA::CachingWalker::getClobberingMemoryAccess(MemoryAccess *MA) { + auto *StartingAccess = dyn_cast<MemoryUseOrDef>(MA); + // If this is a MemoryPhi, we can't do anything. + if (!StartingAccess) + return MA; + + // If this is an already optimized use or def, return the optimized result. + // Note: Currently, we do not store the optimized def result because we'd need + // a separate field, since we can't use it as the defining access. + if (MemoryUse *MU = dyn_cast<MemoryUse>(StartingAccess)) + if (MU->isOptimized()) + return MU->getDefiningAccess(); + + const Instruction *I = StartingAccess->getMemoryInst(); + UpwardsMemoryQuery Q(I, StartingAccess); + // We can't sanely do anything with a fences, they conservatively + // clobber all memory, and have no locations to get pointers from to + // try to disambiguate. + if (!Q.IsCall && I->isFenceLike()) + return StartingAccess; + + if (auto *CacheResult = Cache.lookup(StartingAccess, Q.StartingLoc, Q.IsCall)) + return CacheResult; + + if (isUseTriviallyOptimizableToLiveOnEntry(*MSSA->AA, I)) { + MemoryAccess *LiveOnEntry = MSSA->getLiveOnEntryDef(); + Cache.insert(StartingAccess, LiveOnEntry, Q.StartingLoc, Q.IsCall); + if (MemoryUse *MU = dyn_cast<MemoryUse>(StartingAccess)) + MU->setDefiningAccess(LiveOnEntry, true); + return LiveOnEntry; + } + + // Start with the thing we already think clobbers this location + MemoryAccess *DefiningAccess = StartingAccess->getDefiningAccess(); + + // At this point, DefiningAccess may be the live on entry def. + // If it is, we will not get a better result. + if (MSSA->isLiveOnEntryDef(DefiningAccess)) + return DefiningAccess; + + MemoryAccess *Result = getClobberingMemoryAccess(DefiningAccess, Q); + DEBUG(dbgs() << "Starting Memory SSA clobber for " << *I << " is "); + DEBUG(dbgs() << *DefiningAccess << "\n"); + DEBUG(dbgs() << "Final Memory SSA clobber for " << *I << " is "); + DEBUG(dbgs() << *Result << "\n"); + if (MemoryUse *MU = dyn_cast<MemoryUse>(StartingAccess)) + MU->setDefiningAccess(Result, true); + + return Result; +} + +// Verify that MA doesn't exist in any of the caches. +void MemorySSA::CachingWalker::verifyRemoved(MemoryAccess *MA) { + assert(!Cache.contains(MA) && "Found removed MemoryAccess in cache."); +} + +MemoryAccess * +DoNothingMemorySSAWalker::getClobberingMemoryAccess(MemoryAccess *MA) { + if (auto *Use = dyn_cast<MemoryUseOrDef>(MA)) + return Use->getDefiningAccess(); + return MA; +} + +MemoryAccess *DoNothingMemorySSAWalker::getClobberingMemoryAccess( + MemoryAccess *StartingAccess, const MemoryLocation &) { + if (auto *Use = dyn_cast<MemoryUseOrDef>(StartingAccess)) + return Use->getDefiningAccess(); + return StartingAccess; +} +} // namespace llvm |