//===- MemoryDependenceAnalysis.cpp - Mem Deps Implementation -------------===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// // // This file implements an analysis that determines, for a given memory // operation, what preceding memory operations it depends on. It builds on // alias analysis information, and tries to provide a lazy, caching interface to // a common kind of alias information query. // //===----------------------------------------------------------------------===// #include "llvm/Analysis/MemoryDependenceAnalysis.h" #include "llvm/ADT/DenseMap.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallVector.h" #include "llvm/ADT/Statistic.h" #include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/AssumptionCache.h" #include "llvm/Analysis/MemoryBuiltins.h" #include "llvm/Analysis/MemoryLocation.h" #include "llvm/Analysis/PHITransAddr.h" #include "llvm/Analysis/TargetLibraryInfo.h" #include "llvm/Analysis/ValueTracking.h" #include "llvm/IR/BasicBlock.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/Function.h" #include "llvm/IR/InstrTypes.h" #include "llvm/IR/Instruction.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/LLVMContext.h" #include "llvm/IR/Metadata.h" #include "llvm/IR/Module.h" #include "llvm/IR/PredIteratorCache.h" #include "llvm/IR/Type.h" #include "llvm/IR/Use.h" #include "llvm/IR/Value.h" #include "llvm/InitializePasses.h" #include "llvm/Pass.h" #include "llvm/Support/AtomicOrdering.h" #include "llvm/Support/Casting.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Compiler.h" #include "llvm/Support/Debug.h" #include #include #include #include using namespace llvm; #define DEBUG_TYPE "memdep" STATISTIC(NumCacheNonLocal, "Number of fully cached non-local responses"); STATISTIC(NumCacheDirtyNonLocal, "Number of dirty cached non-local responses"); STATISTIC(NumUncacheNonLocal, "Number of uncached non-local responses"); STATISTIC(NumCacheNonLocalPtr, "Number of fully cached non-local ptr responses"); STATISTIC(NumCacheDirtyNonLocalPtr, "Number of cached, but dirty, non-local ptr responses"); STATISTIC(NumUncacheNonLocalPtr, "Number of uncached non-local ptr responses"); STATISTIC(NumCacheCompleteNonLocalPtr, "Number of block queries that were completely cached"); // Limit for the number of instructions to scan in a block. static cl::opt BlockScanLimit( "memdep-block-scan-limit", cl::Hidden, cl::init(100), cl::desc("The number of instructions to scan in a block in memory " "dependency analysis (default = 100)")); static cl::opt BlockNumberLimit("memdep-block-number-limit", cl::Hidden, cl::init(200), cl::desc("The number of blocks to scan during memory " "dependency analysis (default = 200)")); // Limit on the number of memdep results to process. static const unsigned int NumResultsLimit = 100; /// This is a helper function that removes Val from 'Inst's set in ReverseMap. /// /// If the set becomes empty, remove Inst's entry. template static void RemoveFromReverseMap(DenseMap> &ReverseMap, Instruction *Inst, KeyTy Val) { typename DenseMap>::iterator InstIt = ReverseMap.find(Inst); assert(InstIt != ReverseMap.end() && "Reverse map out of sync?"); bool Found = InstIt->second.erase(Val); assert(Found && "Invalid reverse map!"); (void)Found; if (InstIt->second.empty()) ReverseMap.erase(InstIt); } /// If the given instruction references a specific memory location, fill in Loc /// with the details, otherwise set Loc.Ptr to null. /// /// Returns a ModRefInfo value describing the general behavior of the /// instruction. static ModRefInfo GetLocation(const Instruction *Inst, MemoryLocation &Loc, const TargetLibraryInfo &TLI) { if (const LoadInst *LI = dyn_cast(Inst)) { if (LI->isUnordered()) { Loc = MemoryLocation::get(LI); return ModRefInfo::Ref; } if (LI->getOrdering() == AtomicOrdering::Monotonic) { Loc = MemoryLocation::get(LI); return ModRefInfo::ModRef; } Loc = MemoryLocation(); return ModRefInfo::ModRef; } if (const StoreInst *SI = dyn_cast(Inst)) { if (SI->isUnordered()) { Loc = MemoryLocation::get(SI); return ModRefInfo::Mod; } if (SI->getOrdering() == AtomicOrdering::Monotonic) { Loc = MemoryLocation::get(SI); return ModRefInfo::ModRef; } Loc = MemoryLocation(); return ModRefInfo::ModRef; } if (const VAArgInst *V = dyn_cast(Inst)) { Loc = MemoryLocation::get(V); return ModRefInfo::ModRef; } if (const CallBase *CB = dyn_cast(Inst)) { if (Value *FreedOp = getFreedOperand(CB, &TLI)) { // calls to free() deallocate the entire structure Loc = MemoryLocation::getAfter(FreedOp); return ModRefInfo::Mod; } } if (const IntrinsicInst *II = dyn_cast(Inst)) { switch (II->getIntrinsicID()) { case Intrinsic::lifetime_start: case Intrinsic::lifetime_end: case Intrinsic::invariant_start: Loc = MemoryLocation::getForArgument(II, 1, TLI); // These intrinsics don't really modify the memory, but returning Mod // will allow them to be handled conservatively. return ModRefInfo::Mod; case Intrinsic::invariant_end: Loc = MemoryLocation::getForArgument(II, 2, TLI); // These intrinsics don't really modify the memory, but returning Mod // will allow them to be handled conservatively. return ModRefInfo::Mod; case Intrinsic::masked_load: Loc = MemoryLocation::getForArgument(II, 0, TLI); return ModRefInfo::Ref; case Intrinsic::masked_store: Loc = MemoryLocation::getForArgument(II, 1, TLI); return ModRefInfo::Mod; default: break; } } // Otherwise, just do the coarse-grained thing that always works. if (Inst->mayWriteToMemory()) return ModRefInfo::ModRef; if (Inst->mayReadFromMemory()) return ModRefInfo::Ref; return ModRefInfo::NoModRef; } /// Private helper for finding the local dependencies of a call site. MemDepResult MemoryDependenceResults::getCallDependencyFrom( CallBase *Call, bool isReadOnlyCall, BasicBlock::iterator ScanIt, BasicBlock *BB) { unsigned Limit = getDefaultBlockScanLimit(); // Walk backwards through the block, looking for dependencies. while (ScanIt != BB->begin()) { Instruction *Inst = &*--ScanIt; // Debug intrinsics don't cause dependences and should not affect Limit if (isa(Inst)) continue; // Limit the amount of scanning we do so we don't end up with quadratic // running time on extreme testcases. --Limit; if (!Limit) return MemDepResult::getUnknown(); // If this inst is a memory op, get the pointer it accessed MemoryLocation Loc; ModRefInfo MR = GetLocation(Inst, Loc, TLI); if (Loc.Ptr) { // A simple instruction. if (isModOrRefSet(AA.getModRefInfo(Call, Loc))) return MemDepResult::getClobber(Inst); continue; } if (auto *CallB = dyn_cast(Inst)) { // If these two calls do not interfere, look past it. if (isNoModRef(AA.getModRefInfo(Call, CallB))) { // If the two calls are the same, return Inst as a Def, so that // Call can be found redundant and eliminated. if (isReadOnlyCall && !isModSet(MR) && Call->isIdenticalToWhenDefined(CallB)) return MemDepResult::getDef(Inst); // Otherwise if the two calls don't interact (e.g. CallB is readnone) // keep scanning. continue; } else return MemDepResult::getClobber(Inst); } // If we could not obtain a pointer for the instruction and the instruction // touches memory then assume that this is a dependency. if (isModOrRefSet(MR)) return MemDepResult::getClobber(Inst); } // No dependence found. If this is the entry block of the function, it is // unknown, otherwise it is non-local. if (BB != &BB->getParent()->getEntryBlock()) return MemDepResult::getNonLocal(); return MemDepResult::getNonFuncLocal(); } MemDepResult MemoryDependenceResults::getPointerDependencyFrom( const MemoryLocation &MemLoc, bool isLoad, BasicBlock::iterator ScanIt, BasicBlock *BB, Instruction *QueryInst, unsigned *Limit, BatchAAResults &BatchAA) { MemDepResult InvariantGroupDependency = MemDepResult::getUnknown(); if (QueryInst != nullptr) { if (auto *LI = dyn_cast(QueryInst)) { InvariantGroupDependency = getInvariantGroupPointerDependency(LI, BB); if (InvariantGroupDependency.isDef()) return InvariantGroupDependency; } } MemDepResult SimpleDep = getSimplePointerDependencyFrom( MemLoc, isLoad, ScanIt, BB, QueryInst, Limit, BatchAA); if (SimpleDep.isDef()) return SimpleDep; // Non-local invariant group dependency indicates there is non local Def // (it only returns nonLocal if it finds nonLocal def), which is better than // local clobber and everything else. if (InvariantGroupDependency.isNonLocal()) return InvariantGroupDependency; assert(InvariantGroupDependency.isUnknown() && "InvariantGroupDependency should be only unknown at this point"); return SimpleDep; } MemDepResult MemoryDependenceResults::getPointerDependencyFrom( const MemoryLocation &MemLoc, bool isLoad, BasicBlock::iterator ScanIt, BasicBlock *BB, Instruction *QueryInst, unsigned *Limit) { BatchAAResults BatchAA(AA, &EII); return getPointerDependencyFrom(MemLoc, isLoad, ScanIt, BB, QueryInst, Limit, BatchAA); } MemDepResult MemoryDependenceResults::getInvariantGroupPointerDependency(LoadInst *LI, BasicBlock *BB) { if (!LI->hasMetadata(LLVMContext::MD_invariant_group)) return MemDepResult::getUnknown(); // Take the ptr operand after all casts and geps 0. This way we can search // cast graph down only. Value *LoadOperand = LI->getPointerOperand()->stripPointerCasts(); // It's is not safe to walk the use list of global value, because function // passes aren't allowed to look outside their functions. // FIXME: this could be fixed by filtering instructions from outside // of current function. if (isa(LoadOperand)) return MemDepResult::getUnknown(); // Queue to process all pointers that are equivalent to load operand. SmallVector LoadOperandsQueue; LoadOperandsQueue.push_back(LoadOperand); Instruction *ClosestDependency = nullptr; // Order of instructions in uses list is unpredictible. In order to always // get the same result, we will look for the closest dominance. auto GetClosestDependency = [this](Instruction *Best, Instruction *Other) { assert(Other && "Must call it with not null instruction"); if (Best == nullptr || DT.dominates(Best, Other)) return Other; return Best; }; // FIXME: This loop is O(N^2) because dominates can be O(n) and in worst case // we will see all the instructions. This should be fixed in MSSA. while (!LoadOperandsQueue.empty()) { const Value *Ptr = LoadOperandsQueue.pop_back_val(); assert(Ptr && !isa(Ptr) && "Null or GlobalValue should not be inserted"); for (const Use &Us : Ptr->uses()) { auto *U = dyn_cast(Us.getUser()); if (!U || U == LI || !DT.dominates(U, LI)) continue; // Bitcast or gep with zeros are using Ptr. Add to queue to check it's // users. U = bitcast Ptr if (isa(U)) { LoadOperandsQueue.push_back(U); continue; } // Gep with zeros is equivalent to bitcast. // FIXME: we are not sure if some bitcast should be canonicalized to gep 0 // or gep 0 to bitcast because of SROA, so there are 2 forms. When // typeless pointers will be ready then both cases will be gone // (and this BFS also won't be needed). if (auto *GEP = dyn_cast(U)) if (GEP->hasAllZeroIndices()) { LoadOperandsQueue.push_back(U); continue; } // If we hit load/store with the same invariant.group metadata (and the // same pointer operand) we can assume that value pointed by pointer // operand didn't change. if ((isa(U) || (isa(U) && cast(U)->getPointerOperand() == Ptr)) && U->hasMetadata(LLVMContext::MD_invariant_group)) ClosestDependency = GetClosestDependency(ClosestDependency, U); } } if (!ClosestDependency) return MemDepResult::getUnknown(); if (ClosestDependency->getParent() == BB) return MemDepResult::getDef(ClosestDependency); // Def(U) can't be returned here because it is non-local. If local // dependency won't be found then return nonLocal counting that the // user will call getNonLocalPointerDependency, which will return cached // result. NonLocalDefsCache.try_emplace( LI, NonLocalDepResult(ClosestDependency->getParent(), MemDepResult::getDef(ClosestDependency), nullptr)); ReverseNonLocalDefsCache[ClosestDependency].insert(LI); return MemDepResult::getNonLocal(); } // Check if SI that may alias with MemLoc can be safely skipped. This is // possible in case if SI can only must alias or no alias with MemLoc (no // partial overlapping possible) and it writes the same value that MemLoc // contains now (it was loaded before this store and was not modified in // between). static bool canSkipClobberingStore(const StoreInst *SI, const MemoryLocation &MemLoc, Align MemLocAlign, BatchAAResults &BatchAA, unsigned ScanLimit) { if (!MemLoc.Size.hasValue()) return false; if (MemoryLocation::get(SI).Size != MemLoc.Size) return false; if (MemLoc.Size.isScalable()) return false; if (std::min(MemLocAlign, SI->getAlign()).value() < MemLoc.Size.getValue().getKnownMinValue()) return false; auto *LI = dyn_cast(SI->getValueOperand()); if (!LI || LI->getParent() != SI->getParent()) return false; if (BatchAA.alias(MemoryLocation::get(LI), MemLoc) != AliasResult::MustAlias) return false; unsigned NumVisitedInsts = 0; for (const Instruction *I = LI; I != SI; I = I->getNextNonDebugInstruction()) if (++NumVisitedInsts > ScanLimit || isModSet(BatchAA.getModRefInfo(I, MemLoc))) return false; return true; } MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom( const MemoryLocation &MemLoc, bool isLoad, BasicBlock::iterator ScanIt, BasicBlock *BB, Instruction *QueryInst, unsigned *Limit, BatchAAResults &BatchAA) { bool isInvariantLoad = false; Align MemLocAlign = MemLoc.Ptr->getPointerAlignment(BB->getModule()->getDataLayout()); unsigned DefaultLimit = getDefaultBlockScanLimit(); if (!Limit) Limit = &DefaultLimit; // We must be careful with atomic accesses, as they may allow another thread // to touch this location, clobbering it. We are conservative: if the // QueryInst is not a simple (non-atomic) memory access, we automatically // return getClobber. // If it is simple, we know based on the results of // "Compiler testing via a theory of sound optimisations in the C11/C++11 // memory model" in PLDI 2013, that a non-atomic location can only be // clobbered between a pair of a release and an acquire action, with no // access to the location in between. // Here is an example for giving the general intuition behind this rule. // In the following code: // store x 0; // release action; [1] // acquire action; [4] // %val = load x; // It is unsafe to replace %val by 0 because another thread may be running: // acquire action; [2] // store x 42; // release action; [3] // with synchronization from 1 to 2 and from 3 to 4, resulting in %val // being 42. A key property of this program however is that if either // 1 or 4 were missing, there would be a race between the store of 42 // either the store of 0 or the load (making the whole program racy). // The paper mentioned above shows that the same property is respected // by every program that can detect any optimization of that kind: either // it is racy (undefined) or there is a release followed by an acquire // between the pair of accesses under consideration. // If the load is invariant, we "know" that it doesn't alias *any* write. We // do want to respect mustalias results since defs are useful for value // forwarding, but any mayalias write can be assumed to be noalias. // Arguably, this logic should be pushed inside AliasAnalysis itself. if (isLoad && QueryInst) if (LoadInst *LI = dyn_cast(QueryInst)) { if (LI->hasMetadata(LLVMContext::MD_invariant_load)) isInvariantLoad = true; MemLocAlign = LI->getAlign(); } // True for volatile instruction. // For Load/Store return true if atomic ordering is stronger than AO, // for other instruction just true if it can read or write to memory. auto isComplexForReordering = [](Instruction * I, AtomicOrdering AO)->bool { if (I->isVolatile()) return true; if (auto *LI = dyn_cast(I)) return isStrongerThan(LI->getOrdering(), AO); if (auto *SI = dyn_cast(I)) return isStrongerThan(SI->getOrdering(), AO); return I->mayReadOrWriteMemory(); }; // Walk backwards through the basic block, looking for dependencies. while (ScanIt != BB->begin()) { Instruction *Inst = &*--ScanIt; if (IntrinsicInst *II = dyn_cast(Inst)) // Debug intrinsics don't (and can't) cause dependencies. if (isa(II)) continue; // Limit the amount of scanning we do so we don't end up with quadratic // running time on extreme testcases. --*Limit; if (!*Limit) return MemDepResult::getUnknown(); if (IntrinsicInst *II = dyn_cast(Inst)) { // If we reach a lifetime begin or end marker, then the query ends here // because the value is undefined. Intrinsic::ID ID = II->getIntrinsicID(); switch (ID) { case Intrinsic::lifetime_start: { // FIXME: This only considers queries directly on the invariant-tagged // pointer, not on query pointers that are indexed off of them. It'd // be nice to handle that at some point (the right approach is to use // GetPointerBaseWithConstantOffset). MemoryLocation ArgLoc = MemoryLocation::getAfter(II->getArgOperand(1)); if (BatchAA.isMustAlias(ArgLoc, MemLoc)) return MemDepResult::getDef(II); continue; } case Intrinsic::masked_load: case Intrinsic::masked_store: { MemoryLocation Loc; /*ModRefInfo MR =*/ GetLocation(II, Loc, TLI); AliasResult R = BatchAA.alias(Loc, MemLoc); if (R == AliasResult::NoAlias) continue; if (R == AliasResult::MustAlias) return MemDepResult::getDef(II); if (ID == Intrinsic::masked_load) continue; return MemDepResult::getClobber(II); } } } // Values depend on loads if the pointers are must aliased. This means // that a load depends on another must aliased load from the same value. // One exception is atomic loads: a value can depend on an atomic load that // it does not alias with when this atomic load indicates that another // thread may be accessing the location. if (LoadInst *LI = dyn_cast(Inst)) { // While volatile access cannot be eliminated, they do not have to clobber // non-aliasing locations, as normal accesses, for example, can be safely // reordered with volatile accesses. if (LI->isVolatile()) { if (!QueryInst) // Original QueryInst *may* be volatile return MemDepResult::getClobber(LI); if (QueryInst->isVolatile()) // Ordering required if QueryInst is itself volatile return MemDepResult::getClobber(LI); // Otherwise, volatile doesn't imply any special ordering } // Atomic loads have complications involved. // A Monotonic (or higher) load is OK if the query inst is itself not // atomic. // FIXME: This is overly conservative. if (LI->isAtomic() && isStrongerThanUnordered(LI->getOrdering())) { if (!QueryInst || isComplexForReordering(QueryInst, AtomicOrdering::NotAtomic)) return MemDepResult::getClobber(LI); if (LI->getOrdering() != AtomicOrdering::Monotonic) return MemDepResult::getClobber(LI); } MemoryLocation LoadLoc = MemoryLocation::get(LI); // If we found a pointer, check if it could be the same as our pointer. AliasResult R = BatchAA.alias(LoadLoc, MemLoc); if (R == AliasResult::NoAlias) continue; if (isLoad) { // Must aliased loads are defs of each other. if (R == AliasResult::MustAlias) return MemDepResult::getDef(Inst); // If we have a partial alias, then return this as a clobber for the // client to handle. if (R == AliasResult::PartialAlias && R.hasOffset()) { ClobberOffsets[LI] = R.getOffset(); return MemDepResult::getClobber(Inst); } // Random may-alias loads don't depend on each other without a // dependence. continue; } // Stores don't alias loads from read-only memory. if (!isModSet(BatchAA.getModRefInfoMask(LoadLoc))) continue; // Stores depend on may/must aliased loads. return MemDepResult::getDef(Inst); } if (StoreInst *SI = dyn_cast(Inst)) { // Atomic stores have complications involved. // A Monotonic store is OK if the query inst is itself not atomic. // FIXME: This is overly conservative. if (!SI->isUnordered() && SI->isAtomic()) { if (!QueryInst || isComplexForReordering(QueryInst, AtomicOrdering::Unordered)) return MemDepResult::getClobber(SI); // Ok, if we are here the guard above guarantee us that // QueryInst is a non-atomic or unordered load/store. // SI is atomic with monotonic or release semantic (seq_cst for store // is actually a release semantic plus total order over other seq_cst // instructions, as soon as QueryInst is not seq_cst we can consider it // as simple release semantic). // Monotonic and Release semantic allows re-ordering before store // so we are safe to go further and check the aliasing. It will prohibit // re-ordering in case locations are may or must alias. } // While volatile access cannot be eliminated, they do not have to clobber // non-aliasing locations, as normal accesses can for example be reordered // with volatile accesses. if (SI->isVolatile()) if (!QueryInst || QueryInst->isVolatile()) return MemDepResult::getClobber(SI); // If alias analysis can tell that this store is guaranteed to not modify // the query pointer, ignore it. Use getModRefInfo to handle cases where // the query pointer points to constant memory etc. if (!isModOrRefSet(BatchAA.getModRefInfo(SI, MemLoc))) continue; // Ok, this store might clobber the query pointer. Check to see if it is // a must alias: in this case, we want to return this as a def. // FIXME: Use ModRefInfo::Must bit from getModRefInfo call above. MemoryLocation StoreLoc = MemoryLocation::get(SI); // If we found a pointer, check if it could be the same as our pointer. AliasResult R = BatchAA.alias(StoreLoc, MemLoc); if (R == AliasResult::NoAlias) continue; if (R == AliasResult::MustAlias) return MemDepResult::getDef(Inst); if (isInvariantLoad) continue; if (canSkipClobberingStore(SI, MemLoc, MemLocAlign, BatchAA, *Limit)) continue; return MemDepResult::getClobber(Inst); } // If this is an allocation, and if we know that the accessed pointer is to // the allocation, return Def. This means that there is no dependence and // the access can be optimized based on that. For example, a load could // turn into undef. Note that we can bypass the allocation itself when // looking for a clobber in many cases; that's an alias property and is // handled by BasicAA. if (isa(Inst) || isNoAliasCall(Inst)) { const Value *AccessPtr = getUnderlyingObject(MemLoc.Ptr); if (AccessPtr == Inst || BatchAA.isMustAlias(Inst, AccessPtr)) return MemDepResult::getDef(Inst); } // If we found a select instruction for MemLoc pointer, return it as Def // dependency. if (isa(Inst) && MemLoc.Ptr == Inst) return MemDepResult::getDef(Inst); if (isInvariantLoad) continue; // A release fence requires that all stores complete before it, but does // not prevent the reordering of following loads or stores 'before' the // fence. As a result, we look past it when finding a dependency for // loads. DSE uses this to find preceding stores to delete and thus we // can't bypass the fence if the query instruction is a store. if (FenceInst *FI = dyn_cast(Inst)) if (isLoad && FI->getOrdering() == AtomicOrdering::Release) continue; // See if this instruction (e.g. a call or vaarg) mod/ref's the pointer. switch (BatchAA.getModRefInfo(Inst, MemLoc)) { case ModRefInfo::NoModRef: // If the call has no effect on the queried pointer, just ignore it. continue; case ModRefInfo::Mod: return MemDepResult::getClobber(Inst); case ModRefInfo::Ref: // If the call is known to never store to the pointer, and if this is a // load query, we can safely ignore it (scan past it). if (isLoad) continue; [[fallthrough]]; default: // Otherwise, there is a potential dependence. Return a clobber. return MemDepResult::getClobber(Inst); } } // No dependence found. If this is the entry block of the function, it is // unknown, otherwise it is non-local. if (BB != &BB->getParent()->getEntryBlock()) return MemDepResult::getNonLocal(); return MemDepResult::getNonFuncLocal(); } MemDepResult MemoryDependenceResults::getDependency(Instruction *QueryInst) { ClobberOffsets.clear(); Instruction *ScanPos = QueryInst; // Check for a cached result MemDepResult &LocalCache = LocalDeps[QueryInst]; // If the cached entry is non-dirty, just return it. Note that this depends // on MemDepResult's default constructing to 'dirty'. if (!LocalCache.isDirty()) return LocalCache; // Otherwise, if we have a dirty entry, we know we can start the scan at that // instruction, which may save us some work. if (Instruction *Inst = LocalCache.getInst()) { ScanPos = Inst; RemoveFromReverseMap(ReverseLocalDeps, Inst, QueryInst); } BasicBlock *QueryParent = QueryInst->getParent(); // Do the scan. if (BasicBlock::iterator(QueryInst) == QueryParent->begin()) { // No dependence found. If this is the entry block of the function, it is // unknown, otherwise it is non-local. if (QueryParent != &QueryParent->getParent()->getEntryBlock()) LocalCache = MemDepResult::getNonLocal(); else LocalCache = MemDepResult::getNonFuncLocal(); } else { MemoryLocation MemLoc; ModRefInfo MR = GetLocation(QueryInst, MemLoc, TLI); if (MemLoc.Ptr) { // If we can do a pointer scan, make it happen. bool isLoad = !isModSet(MR); if (auto *II = dyn_cast(QueryInst)) isLoad |= II->getIntrinsicID() == Intrinsic::lifetime_start; LocalCache = getPointerDependencyFrom(MemLoc, isLoad, ScanPos->getIterator(), QueryParent, QueryInst, nullptr); } else if (auto *QueryCall = dyn_cast(QueryInst)) { bool isReadOnly = AA.onlyReadsMemory(QueryCall); LocalCache = getCallDependencyFrom(QueryCall, isReadOnly, ScanPos->getIterator(), QueryParent); } else // Non-memory instruction. LocalCache = MemDepResult::getUnknown(); } // Remember the result! if (Instruction *I = LocalCache.getInst()) ReverseLocalDeps[I].insert(QueryInst); return LocalCache; } #ifndef NDEBUG /// This method is used when -debug is specified to verify that cache arrays /// are properly kept sorted. static void AssertSorted(MemoryDependenceResults::NonLocalDepInfo &Cache, int Count = -1) { if (Count == -1) Count = Cache.size(); assert(std::is_sorted(Cache.begin(), Cache.begin() + Count) && "Cache isn't sorted!"); } #endif const MemoryDependenceResults::NonLocalDepInfo & MemoryDependenceResults::getNonLocalCallDependency(CallBase *QueryCall) { assert(getDependency(QueryCall).isNonLocal() && "getNonLocalCallDependency should only be used on calls with " "non-local deps!"); PerInstNLInfo &CacheP = NonLocalDepsMap[QueryCall]; NonLocalDepInfo &Cache = CacheP.first; // This is the set of blocks that need to be recomputed. In the cached case, // this can happen due to instructions being deleted etc. In the uncached // case, this starts out as the set of predecessors we care about. SmallVector DirtyBlocks; if (!Cache.empty()) { // Okay, we have a cache entry. If we know it is not dirty, just return it // with no computation. if (!CacheP.second) { ++NumCacheNonLocal; return Cache; } // If we already have a partially computed set of results, scan them to // determine what is dirty, seeding our initial DirtyBlocks worklist. for (auto &Entry : Cache) if (Entry.getResult().isDirty()) DirtyBlocks.push_back(Entry.getBB()); // Sort the cache so that we can do fast binary search lookups below. llvm::sort(Cache); ++NumCacheDirtyNonLocal; } else { // Seed DirtyBlocks with each of the preds of QueryInst's block. BasicBlock *QueryBB = QueryCall->getParent(); append_range(DirtyBlocks, PredCache.get(QueryBB)); ++NumUncacheNonLocal; } // isReadonlyCall - If this is a read-only call, we can be more aggressive. bool isReadonlyCall = AA.onlyReadsMemory(QueryCall); SmallPtrSet Visited; unsigned NumSortedEntries = Cache.size(); LLVM_DEBUG(AssertSorted(Cache)); // Iterate while we still have blocks to update. while (!DirtyBlocks.empty()) { BasicBlock *DirtyBB = DirtyBlocks.pop_back_val(); // Already processed this block? if (!Visited.insert(DirtyBB).second) continue; // Do a binary search to see if we already have an entry for this block in // the cache set. If so, find it. LLVM_DEBUG(AssertSorted(Cache, NumSortedEntries)); NonLocalDepInfo::iterator Entry = std::upper_bound(Cache.begin(), Cache.begin() + NumSortedEntries, NonLocalDepEntry(DirtyBB)); if (Entry != Cache.begin() && std::prev(Entry)->getBB() == DirtyBB) --Entry; NonLocalDepEntry *ExistingResult = nullptr; if (Entry != Cache.begin() + NumSortedEntries && Entry->getBB() == DirtyBB) { // If we already have an entry, and if it isn't already dirty, the block // is done. if (!Entry->getResult().isDirty()) continue; // Otherwise, remember this slot so we can update the value. ExistingResult = &*Entry; } // If the dirty entry has a pointer, start scanning from it so we don't have // to rescan the entire block. BasicBlock::iterator ScanPos = DirtyBB->end(); if (ExistingResult) { if (Instruction *Inst = ExistingResult->getResult().getInst()) { ScanPos = Inst->getIterator(); // We're removing QueryInst's use of Inst. RemoveFromReverseMap(ReverseNonLocalDeps, Inst, QueryCall); } } // Find out if this block has a local dependency for QueryInst. MemDepResult Dep; if (ScanPos != DirtyBB->begin()) { Dep = getCallDependencyFrom(QueryCall, isReadonlyCall, ScanPos, DirtyBB); } else if (DirtyBB != &DirtyBB->getParent()->getEntryBlock()) { // No dependence found. If this is the entry block of the function, it is // a clobber, otherwise it is unknown. Dep = MemDepResult::getNonLocal(); } else { Dep = MemDepResult::getNonFuncLocal(); } // If we had a dirty entry for the block, update it. Otherwise, just add // a new entry. if (ExistingResult) ExistingResult->setResult(Dep); else Cache.push_back(NonLocalDepEntry(DirtyBB, Dep)); // If the block has a dependency (i.e. it isn't completely transparent to // the value), remember the association! if (!Dep.isNonLocal()) { // Keep the ReverseNonLocalDeps map up to date so we can efficiently // update this when we remove instructions. if (Instruction *Inst = Dep.getInst()) ReverseNonLocalDeps[Inst].insert(QueryCall); } else { // If the block *is* completely transparent to the load, we need to check // the predecessors of this block. Add them to our worklist. append_range(DirtyBlocks, PredCache.get(DirtyBB)); } } return Cache; } void MemoryDependenceResults::getNonLocalPointerDependency( Instruction *QueryInst, SmallVectorImpl &Result) { const MemoryLocation Loc = MemoryLocation::get(QueryInst); bool isLoad = isa(QueryInst); BasicBlock *FromBB = QueryInst->getParent(); assert(FromBB); assert(Loc.Ptr->getType()->isPointerTy() && "Can't get pointer deps of a non-pointer!"); Result.clear(); { // Check if there is cached Def with invariant.group. auto NonLocalDefIt = NonLocalDefsCache.find(QueryInst); if (NonLocalDefIt != NonLocalDefsCache.end()) { Result.push_back(NonLocalDefIt->second); ReverseNonLocalDefsCache[NonLocalDefIt->second.getResult().getInst()] .erase(QueryInst); NonLocalDefsCache.erase(NonLocalDefIt); return; } } // This routine does not expect to deal with volatile instructions. // Doing so would require piping through the QueryInst all the way through. // TODO: volatiles can't be elided, but they can be reordered with other // non-volatile accesses. // We currently give up on any instruction which is ordered, but we do handle // atomic instructions which are unordered. // TODO: Handle ordered instructions auto isOrdered = [](Instruction *Inst) { if (LoadInst *LI = dyn_cast(Inst)) { return !LI->isUnordered(); } else if (StoreInst *SI = dyn_cast(Inst)) { return !SI->isUnordered(); } return false; }; if (QueryInst->isVolatile() || isOrdered(QueryInst)) { Result.push_back(NonLocalDepResult(FromBB, MemDepResult::getUnknown(), const_cast(Loc.Ptr))); return; } const DataLayout &DL = FromBB->getModule()->getDataLayout(); PHITransAddr Address(const_cast(Loc.Ptr), DL, &AC); // This is the set of blocks we've inspected, and the pointer we consider in // each block. Because of critical edges, we currently bail out if querying // a block with multiple different pointers. This can happen during PHI // translation. DenseMap Visited; if (getNonLocalPointerDepFromBB(QueryInst, Address, Loc, isLoad, FromBB, Result, Visited, true)) return; Result.clear(); Result.push_back(NonLocalDepResult(FromBB, MemDepResult::getUnknown(), const_cast(Loc.Ptr))); } /// Compute the memdep value for BB with Pointer/PointeeSize using either /// cached information in Cache or by doing a lookup (which may use dirty cache /// info if available). /// /// If we do a lookup, add the result to the cache. MemDepResult MemoryDependenceResults::getNonLocalInfoForBlock( Instruction *QueryInst, const MemoryLocation &Loc, bool isLoad, BasicBlock *BB, NonLocalDepInfo *Cache, unsigned NumSortedEntries, BatchAAResults &BatchAA) { bool isInvariantLoad = false; if (LoadInst *LI = dyn_cast_or_null(QueryInst)) isInvariantLoad = LI->getMetadata(LLVMContext::MD_invariant_load); // Do a binary search to see if we already have an entry for this block in // the cache set. If so, find it. NonLocalDepInfo::iterator Entry = std::upper_bound( Cache->begin(), Cache->begin() + NumSortedEntries, NonLocalDepEntry(BB)); if (Entry != Cache->begin() && (Entry - 1)->getBB() == BB) --Entry; NonLocalDepEntry *ExistingResult = nullptr; if (Entry != Cache->begin() + NumSortedEntries && Entry->getBB() == BB) ExistingResult = &*Entry; // Use cached result for invariant load only if there is no dependency for non // invariant load. In this case invariant load can not have any dependency as // well. if (ExistingResult && isInvariantLoad && !ExistingResult->getResult().isNonFuncLocal()) ExistingResult = nullptr; // If we have a cached entry, and it is non-dirty, use it as the value for // this dependency. if (ExistingResult && !ExistingResult->getResult().isDirty()) { ++NumCacheNonLocalPtr; return ExistingResult->getResult(); } // Otherwise, we have to scan for the value. If we have a dirty cache // entry, start scanning from its position, otherwise we scan from the end // of the block. BasicBlock::iterator ScanPos = BB->end(); if (ExistingResult && ExistingResult->getResult().getInst()) { assert(ExistingResult->getResult().getInst()->getParent() == BB && "Instruction invalidated?"); ++NumCacheDirtyNonLocalPtr; ScanPos = ExistingResult->getResult().getInst()->getIterator(); // Eliminating the dirty entry from 'Cache', so update the reverse info. ValueIsLoadPair CacheKey(Loc.Ptr, isLoad); RemoveFromReverseMap(ReverseNonLocalPtrDeps, &*ScanPos, CacheKey); } else { ++NumUncacheNonLocalPtr; } // Scan the block for the dependency. MemDepResult Dep = getPointerDependencyFrom(Loc, isLoad, ScanPos, BB, QueryInst, nullptr, BatchAA); // Don't cache results for invariant load. if (isInvariantLoad) return Dep; // If we had a dirty entry for the block, update it. Otherwise, just add // a new entry. if (ExistingResult) ExistingResult->setResult(Dep); else Cache->push_back(NonLocalDepEntry(BB, Dep)); // If the block has a dependency (i.e. it isn't completely transparent to // the value), remember the reverse association because we just added it // to Cache! if (!Dep.isLocal()) return Dep; // Keep the ReverseNonLocalPtrDeps map up to date so we can efficiently // update MemDep when we remove instructions. Instruction *Inst = Dep.getInst(); assert(Inst && "Didn't depend on anything?"); ValueIsLoadPair CacheKey(Loc.Ptr, isLoad); ReverseNonLocalPtrDeps[Inst].insert(CacheKey); return Dep; } /// Sort the NonLocalDepInfo cache, given a certain number of elements in the /// array that are already properly ordered. /// /// This is optimized for the case when only a few entries are added. static void SortNonLocalDepInfoCache(MemoryDependenceResults::NonLocalDepInfo &Cache, unsigned NumSortedEntries) { switch (Cache.size() - NumSortedEntries) { case 0: // done, no new entries. break; case 2: { // Two new entries, insert the last one into place. NonLocalDepEntry Val = Cache.back(); Cache.pop_back(); MemoryDependenceResults::NonLocalDepInfo::iterator Entry = std::upper_bound(Cache.begin(), Cache.end() - 1, Val); Cache.insert(Entry, Val); [[fallthrough]]; } case 1: // One new entry, Just insert the new value at the appropriate position. if (Cache.size() != 1) { NonLocalDepEntry Val = Cache.back(); Cache.pop_back(); MemoryDependenceResults::NonLocalDepInfo::iterator Entry = llvm::upper_bound(Cache, Val); Cache.insert(Entry, Val); } break; default: // Added many values, do a full scale sort. llvm::sort(Cache); break; } } /// Perform a dependency query based on pointer/pointeesize starting at the end /// of StartBB. /// /// Add any clobber/def results to the results vector and keep track of which /// blocks are visited in 'Visited'. /// /// This has special behavior for the first block queries (when SkipFirstBlock /// is true). In this special case, it ignores the contents of the specified /// block and starts returning dependence info for its predecessors. /// /// This function returns true on success, or false to indicate that it could /// not compute dependence information for some reason. This should be treated /// as a clobber dependence on the first instruction in the predecessor block. bool MemoryDependenceResults::getNonLocalPointerDepFromBB( Instruction *QueryInst, const PHITransAddr &Pointer, const MemoryLocation &Loc, bool isLoad, BasicBlock *StartBB, SmallVectorImpl &Result, DenseMap &Visited, bool SkipFirstBlock, bool IsIncomplete) { // Look up the cached info for Pointer. ValueIsLoadPair CacheKey(Pointer.getAddr(), isLoad); // Set up a temporary NLPI value. If the map doesn't yet have an entry for // CacheKey, this value will be inserted as the associated value. Otherwise, // it'll be ignored, and we'll have to check to see if the cached size and // aa tags are consistent with the current query. NonLocalPointerInfo InitialNLPI; InitialNLPI.Size = Loc.Size; InitialNLPI.AATags = Loc.AATags; bool isInvariantLoad = false; if (LoadInst *LI = dyn_cast_or_null(QueryInst)) isInvariantLoad = LI->getMetadata(LLVMContext::MD_invariant_load); // Get the NLPI for CacheKey, inserting one into the map if it doesn't // already have one. std::pair Pair = NonLocalPointerDeps.insert(std::make_pair(CacheKey, InitialNLPI)); NonLocalPointerInfo *CacheInfo = &Pair.first->second; // If we already have a cache entry for this CacheKey, we may need to do some // work to reconcile the cache entry and the current query. // Invariant loads don't participate in caching. Thus no need to reconcile. if (!isInvariantLoad && !Pair.second) { if (CacheInfo->Size != Loc.Size) { bool ThrowOutEverything; if (CacheInfo->Size.hasValue() && Loc.Size.hasValue()) { // FIXME: We may be able to do better in the face of results with mixed // precision. We don't appear to get them in practice, though, so just // be conservative. ThrowOutEverything = CacheInfo->Size.isPrecise() != Loc.Size.isPrecise() || !TypeSize::isKnownGE(CacheInfo->Size.getValue(), Loc.Size.getValue()); } else { // For our purposes, unknown size > all others. ThrowOutEverything = !Loc.Size.hasValue(); } if (ThrowOutEverything) { // The query's Size is greater than the cached one. Throw out the // cached data and proceed with the query at the greater size. CacheInfo->Pair = BBSkipFirstBlockPair(); CacheInfo->Size = Loc.Size; for (auto &Entry : CacheInfo->NonLocalDeps) if (Instruction *Inst = Entry.getResult().getInst()) RemoveFromReverseMap(ReverseNonLocalPtrDeps, Inst, CacheKey); CacheInfo->NonLocalDeps.clear(); // The cache is cleared (in the above line) so we will have lost // information about blocks we have already visited. We therefore must // assume that the cache information is incomplete. IsIncomplete = true; } else { // This query's Size is less than the cached one. Conservatively restart // the query using the greater size. return getNonLocalPointerDepFromBB( QueryInst, Pointer, Loc.getWithNewSize(CacheInfo->Size), isLoad, StartBB, Result, Visited, SkipFirstBlock, IsIncomplete); } } // If the query's AATags are inconsistent with the cached one, // conservatively throw out the cached data and restart the query with // no tag if needed. if (CacheInfo->AATags != Loc.AATags) { if (CacheInfo->AATags) { CacheInfo->Pair = BBSkipFirstBlockPair(); CacheInfo->AATags = AAMDNodes(); for (auto &Entry : CacheInfo->NonLocalDeps) if (Instruction *Inst = Entry.getResult().getInst()) RemoveFromReverseMap(ReverseNonLocalPtrDeps, Inst, CacheKey); CacheInfo->NonLocalDeps.clear(); // The cache is cleared (in the above line) so we will have lost // information about blocks we have already visited. We therefore must // assume that the cache information is incomplete. IsIncomplete = true; } if (Loc.AATags) return getNonLocalPointerDepFromBB( QueryInst, Pointer, Loc.getWithoutAATags(), isLoad, StartBB, Result, Visited, SkipFirstBlock, IsIncomplete); } } NonLocalDepInfo *Cache = &CacheInfo->NonLocalDeps; // If we have valid cached information for exactly the block we are // investigating, just return it with no recomputation. // Don't use cached information for invariant loads since it is valid for // non-invariant loads only. if (!IsIncomplete && !isInvariantLoad && CacheInfo->Pair == BBSkipFirstBlockPair(StartBB, SkipFirstBlock)) { // We have a fully cached result for this query then we can just return the // cached results and populate the visited set. However, we have to verify // that we don't already have conflicting results for these blocks. Check // to ensure that if a block in the results set is in the visited set that // it was for the same pointer query. if (!Visited.empty()) { for (auto &Entry : *Cache) { DenseMap::iterator VI = Visited.find(Entry.getBB()); if (VI == Visited.end() || VI->second == Pointer.getAddr()) continue; // We have a pointer mismatch in a block. Just return false, saying // that something was clobbered in this result. We could also do a // non-fully cached query, but there is little point in doing this. return false; } } Value *Addr = Pointer.getAddr(); for (auto &Entry : *Cache) { Visited.insert(std::make_pair(Entry.getBB(), Addr)); if (Entry.getResult().isNonLocal()) { continue; } if (DT.isReachableFromEntry(Entry.getBB())) { Result.push_back( NonLocalDepResult(Entry.getBB(), Entry.getResult(), Addr)); } } ++NumCacheCompleteNonLocalPtr; return true; } // Otherwise, either this is a new block, a block with an invalid cache // pointer or one that we're about to invalidate by putting more info into // it than its valid cache info. If empty and not explicitly indicated as // incomplete, the result will be valid cache info, otherwise it isn't. // // Invariant loads don't affect cache in any way thus no need to update // CacheInfo as well. if (!isInvariantLoad) { if (!IsIncomplete && Cache->empty()) CacheInfo->Pair = BBSkipFirstBlockPair(StartBB, SkipFirstBlock); else CacheInfo->Pair = BBSkipFirstBlockPair(); } SmallVector Worklist; Worklist.push_back(StartBB); // PredList used inside loop. SmallVector, 16> PredList; // Keep track of the entries that we know are sorted. Previously cached // entries will all be sorted. The entries we add we only sort on demand (we // don't insert every element into its sorted position). We know that we // won't get any reuse from currently inserted values, because we don't // revisit blocks after we insert info for them. unsigned NumSortedEntries = Cache->size(); unsigned WorklistEntries = BlockNumberLimit; bool GotWorklistLimit = false; LLVM_DEBUG(AssertSorted(*Cache)); BatchAAResults BatchAA(AA, &EII); while (!Worklist.empty()) { BasicBlock *BB = Worklist.pop_back_val(); // If we do process a large number of blocks it becomes very expensive and // likely it isn't worth worrying about if (Result.size() > NumResultsLimit) { // Sort it now (if needed) so that recursive invocations of // getNonLocalPointerDepFromBB and other routines that could reuse the // cache value will only see properly sorted cache arrays. if (Cache && NumSortedEntries != Cache->size()) { SortNonLocalDepInfoCache(*Cache, NumSortedEntries); } // Since we bail out, the "Cache" set won't contain all of the // results for the query. This is ok (we can still use it to accelerate // specific block queries) but we can't do the fastpath "return all // results from the set". Clear out the indicator for this. CacheInfo->Pair = BBSkipFirstBlockPair(); return false; } // Skip the first block if we have it. if (!SkipFirstBlock) { // Analyze the dependency of *Pointer in FromBB. See if we already have // been here. assert(Visited.count(BB) && "Should check 'visited' before adding to WL"); // Get the dependency info for Pointer in BB. If we have cached // information, we will use it, otherwise we compute it. LLVM_DEBUG(AssertSorted(*Cache, NumSortedEntries)); MemDepResult Dep = getNonLocalInfoForBlock( QueryInst, Loc, isLoad, BB, Cache, NumSortedEntries, BatchAA); // If we got a Def or Clobber, add this to the list of results. if (!Dep.isNonLocal()) { if (DT.isReachableFromEntry(BB)) { Result.push_back(NonLocalDepResult(BB, Dep, Pointer.getAddr())); continue; } } } // If 'Pointer' is an instruction defined in this block, then we need to do // phi translation to change it into a value live in the predecessor block. // If not, we just add the predecessors to the worklist and scan them with // the same Pointer. if (!Pointer.needsPHITranslationFromBlock(BB)) { SkipFirstBlock = false; SmallVector NewBlocks; for (BasicBlock *Pred : PredCache.get(BB)) { // Verify that we haven't looked at this block yet. std::pair::iterator, bool> InsertRes = Visited.insert(std::make_pair(Pred, Pointer.getAddr())); if (InsertRes.second) { // First time we've looked at *PI. NewBlocks.push_back(Pred); continue; } // If we have seen this block before, but it was with a different // pointer then we have a phi translation failure and we have to treat // this as a clobber. if (InsertRes.first->second != Pointer.getAddr()) { // Make sure to clean up the Visited map before continuing on to // PredTranslationFailure. for (unsigned i = 0; i < NewBlocks.size(); i++) Visited.erase(NewBlocks[i]); goto PredTranslationFailure; } } if (NewBlocks.size() > WorklistEntries) { // Make sure to clean up the Visited map before continuing on to // PredTranslationFailure. for (unsigned i = 0; i < NewBlocks.size(); i++) Visited.erase(NewBlocks[i]); GotWorklistLimit = true; goto PredTranslationFailure; } WorklistEntries -= NewBlocks.size(); Worklist.append(NewBlocks.begin(), NewBlocks.end()); continue; } // We do need to do phi translation, if we know ahead of time we can't phi // translate this value, don't even try. if (!Pointer.isPotentiallyPHITranslatable()) goto PredTranslationFailure; // We may have added values to the cache list before this PHI translation. // If so, we haven't done anything to ensure that the cache remains sorted. // Sort it now (if needed) so that recursive invocations of // getNonLocalPointerDepFromBB and other routines that could reuse the cache // value will only see properly sorted cache arrays. if (Cache && NumSortedEntries != Cache->size()) { SortNonLocalDepInfoCache(*Cache, NumSortedEntries); NumSortedEntries = Cache->size(); } Cache = nullptr; PredList.clear(); for (BasicBlock *Pred : PredCache.get(BB)) { PredList.push_back(std::make_pair(Pred, Pointer)); // Get the PHI translated pointer in this predecessor. This can fail if // not translatable, in which case the getAddr() returns null. PHITransAddr &PredPointer = PredList.back().second; Value *PredPtrVal = PredPointer.translateValue(BB, Pred, &DT, /*MustDominate=*/false); // Check to see if we have already visited this pred block with another // pointer. If so, we can't do this lookup. This failure can occur // with PHI translation when a critical edge exists and the PHI node in // the successor translates to a pointer value different than the // pointer the block was first analyzed with. std::pair::iterator, bool> InsertRes = Visited.insert(std::make_pair(Pred, PredPtrVal)); if (!InsertRes.second) { // We found the pred; take it off the list of preds to visit. PredList.pop_back(); // If the predecessor was visited with PredPtr, then we already did // the analysis and can ignore it. if (InsertRes.first->second == PredPtrVal) continue; // Otherwise, the block was previously analyzed with a different // pointer. We can't represent the result of this case, so we just // treat this as a phi translation failure. // Make sure to clean up the Visited map before continuing on to // PredTranslationFailure. for (unsigned i = 0, n = PredList.size(); i < n; ++i) Visited.erase(PredList[i].first); goto PredTranslationFailure; } } // Actually process results here; this need to be a separate loop to avoid // calling getNonLocalPointerDepFromBB for blocks we don't want to return // any results for. (getNonLocalPointerDepFromBB will modify our // datastructures in ways the code after the PredTranslationFailure label // doesn't expect.) for (unsigned i = 0, n = PredList.size(); i < n; ++i) { BasicBlock *Pred = PredList[i].first; PHITransAddr &PredPointer = PredList[i].second; Value *PredPtrVal = PredPointer.getAddr(); bool CanTranslate = true; // If PHI translation was unable to find an available pointer in this // predecessor, then we have to assume that the pointer is clobbered in // that predecessor. We can still do PRE of the load, which would insert // a computation of the pointer in this predecessor. if (!PredPtrVal) CanTranslate = false; // FIXME: it is entirely possible that PHI translating will end up with // the same value. Consider PHI translating something like: // X = phi [x, bb1], [y, bb2]. PHI translating for bb1 doesn't *need* // to recurse here, pedantically speaking. // If getNonLocalPointerDepFromBB fails here, that means the cached // result conflicted with the Visited list; we have to conservatively // assume it is unknown, but this also does not block PRE of the load. if (!CanTranslate || !getNonLocalPointerDepFromBB(QueryInst, PredPointer, Loc.getWithNewPtr(PredPtrVal), isLoad, Pred, Result, Visited)) { // Add the entry to the Result list. NonLocalDepResult Entry(Pred, MemDepResult::getUnknown(), PredPtrVal); Result.push_back(Entry); // Since we had a phi translation failure, the cache for CacheKey won't // include all of the entries that we need to immediately satisfy future // queries. Mark this in NonLocalPointerDeps by setting the // BBSkipFirstBlockPair pointer to null. This requires reuse of the // cached value to do more work but not miss the phi trans failure. NonLocalPointerInfo &NLPI = NonLocalPointerDeps[CacheKey]; NLPI.Pair = BBSkipFirstBlockPair(); continue; } } // Refresh the CacheInfo/Cache pointer so that it isn't invalidated. CacheInfo = &NonLocalPointerDeps[CacheKey]; Cache = &CacheInfo->NonLocalDeps; NumSortedEntries = Cache->size(); // Since we did phi translation, the "Cache" set won't contain all of the // results for the query. This is ok (we can still use it to accelerate // specific block queries) but we can't do the fastpath "return all // results from the set" Clear out the indicator for this. CacheInfo->Pair = BBSkipFirstBlockPair(); SkipFirstBlock = false; continue; PredTranslationFailure: // The following code is "failure"; we can't produce a sane translation // for the given block. It assumes that we haven't modified any of // our datastructures while processing the current block. if (!Cache) { // Refresh the CacheInfo/Cache pointer if it got invalidated. CacheInfo = &NonLocalPointerDeps[CacheKey]; Cache = &CacheInfo->NonLocalDeps; NumSortedEntries = Cache->size(); } // Since we failed phi translation, the "Cache" set won't contain all of the // results for the query. This is ok (we can still use it to accelerate // specific block queries) but we can't do the fastpath "return all // results from the set". Clear out the indicator for this. CacheInfo->Pair = BBSkipFirstBlockPair(); // If *nothing* works, mark the pointer as unknown. // // If this is the magic first block, return this as a clobber of the whole // incoming value. Since we can't phi translate to one of the predecessors, // we have to bail out. if (SkipFirstBlock) return false; // Results of invariant loads are not cached thus no need to update cached // information. if (!isInvariantLoad) { for (NonLocalDepEntry &I : llvm::reverse(*Cache)) { if (I.getBB() != BB) continue; assert((GotWorklistLimit || I.getResult().isNonLocal() || !DT.isReachableFromEntry(BB)) && "Should only be here with transparent block"); I.setResult(MemDepResult::getUnknown()); break; } } (void)GotWorklistLimit; // Go ahead and report unknown dependence. Result.push_back( NonLocalDepResult(BB, MemDepResult::getUnknown(), Pointer.getAddr())); } // Okay, we're done now. If we added new values to the cache, re-sort it. SortNonLocalDepInfoCache(*Cache, NumSortedEntries); LLVM_DEBUG(AssertSorted(*Cache)); return true; } /// If P exists in CachedNonLocalPointerInfo or NonLocalDefsCache, remove it. void MemoryDependenceResults::removeCachedNonLocalPointerDependencies( ValueIsLoadPair P) { // Most of the time this cache is empty. if (!NonLocalDefsCache.empty()) { auto it = NonLocalDefsCache.find(P.getPointer()); if (it != NonLocalDefsCache.end()) { RemoveFromReverseMap(ReverseNonLocalDefsCache, it->second.getResult().getInst(), P.getPointer()); NonLocalDefsCache.erase(it); } if (auto *I = dyn_cast(P.getPointer())) { auto toRemoveIt = ReverseNonLocalDefsCache.find(I); if (toRemoveIt != ReverseNonLocalDefsCache.end()) { for (const auto *entry : toRemoveIt->second) NonLocalDefsCache.erase(entry); ReverseNonLocalDefsCache.erase(toRemoveIt); } } } CachedNonLocalPointerInfo::iterator It = NonLocalPointerDeps.find(P); if (It == NonLocalPointerDeps.end()) return; // Remove all of the entries in the BB->val map. This involves removing // instructions from the reverse map. NonLocalDepInfo &PInfo = It->second.NonLocalDeps; for (const NonLocalDepEntry &DE : PInfo) { Instruction *Target = DE.getResult().getInst(); if (!Target) continue; // Ignore non-local dep results. assert(Target->getParent() == DE.getBB()); // Eliminating the dirty entry from 'Cache', so update the reverse info. RemoveFromReverseMap(ReverseNonLocalPtrDeps, Target, P); } // Remove P from NonLocalPointerDeps (which deletes NonLocalDepInfo). NonLocalPointerDeps.erase(It); } void MemoryDependenceResults::invalidateCachedPointerInfo(Value *Ptr) { // If Ptr isn't really a pointer, just ignore it. if (!Ptr->getType()->isPointerTy()) return; // Flush store info for the pointer. removeCachedNonLocalPointerDependencies(ValueIsLoadPair(Ptr, false)); // Flush load info for the pointer. removeCachedNonLocalPointerDependencies(ValueIsLoadPair(Ptr, true)); } void MemoryDependenceResults::invalidateCachedPredecessors() { PredCache.clear(); } void MemoryDependenceResults::removeInstruction(Instruction *RemInst) { EII.removeInstruction(RemInst); // Walk through the Non-local dependencies, removing this one as the value // for any cached queries. NonLocalDepMapType::iterator NLDI = NonLocalDepsMap.find(RemInst); if (NLDI != NonLocalDepsMap.end()) { NonLocalDepInfo &BlockMap = NLDI->second.first; for (auto &Entry : BlockMap) if (Instruction *Inst = Entry.getResult().getInst()) RemoveFromReverseMap(ReverseNonLocalDeps, Inst, RemInst); NonLocalDepsMap.erase(NLDI); } // If we have a cached local dependence query for this instruction, remove it. LocalDepMapType::iterator LocalDepEntry = LocalDeps.find(RemInst); if (LocalDepEntry != LocalDeps.end()) { // Remove us from DepInst's reverse set now that the local dep info is gone. if (Instruction *Inst = LocalDepEntry->second.getInst()) RemoveFromReverseMap(ReverseLocalDeps, Inst, RemInst); // Remove this local dependency info. LocalDeps.erase(LocalDepEntry); } // If we have any cached dependencies on this instruction, remove // them. // If the instruction is a pointer, remove it from both the load info and the // store info. if (RemInst->getType()->isPointerTy()) { removeCachedNonLocalPointerDependencies(ValueIsLoadPair(RemInst, false)); removeCachedNonLocalPointerDependencies(ValueIsLoadPair(RemInst, true)); } else { // Otherwise, if the instructions is in the map directly, it must be a load. // Remove it. auto toRemoveIt = NonLocalDefsCache.find(RemInst); if (toRemoveIt != NonLocalDefsCache.end()) { assert(isa(RemInst) && "only load instructions should be added directly"); const Instruction *DepV = toRemoveIt->second.getResult().getInst(); ReverseNonLocalDefsCache.find(DepV)->second.erase(RemInst); NonLocalDefsCache.erase(toRemoveIt); } } // Loop over all of the things that depend on the instruction we're removing. SmallVector, 8> ReverseDepsToAdd; // If we find RemInst as a clobber or Def in any of the maps for other values, // we need to replace its entry with a dirty version of the instruction after // it. If RemInst is a terminator, we use a null dirty value. // // Using a dirty version of the instruction after RemInst saves having to scan // the entire block to get to this point. MemDepResult NewDirtyVal; if (!RemInst->isTerminator()) NewDirtyVal = MemDepResult::getDirty(&*++RemInst->getIterator()); ReverseDepMapType::iterator ReverseDepIt = ReverseLocalDeps.find(RemInst); if (ReverseDepIt != ReverseLocalDeps.end()) { // RemInst can't be the terminator if it has local stuff depending on it. assert(!ReverseDepIt->second.empty() && !RemInst->isTerminator() && "Nothing can locally depend on a terminator"); for (Instruction *InstDependingOnRemInst : ReverseDepIt->second) { assert(InstDependingOnRemInst != RemInst && "Already removed our local dep info"); LocalDeps[InstDependingOnRemInst] = NewDirtyVal; // Make sure to remember that new things depend on NewDepInst. assert(NewDirtyVal.getInst() && "There is no way something else can have " "a local dep on this if it is a terminator!"); ReverseDepsToAdd.push_back( std::make_pair(NewDirtyVal.getInst(), InstDependingOnRemInst)); } ReverseLocalDeps.erase(ReverseDepIt); // Add new reverse deps after scanning the set, to avoid invalidating the // 'ReverseDeps' reference. while (!ReverseDepsToAdd.empty()) { ReverseLocalDeps[ReverseDepsToAdd.back().first].insert( ReverseDepsToAdd.back().second); ReverseDepsToAdd.pop_back(); } } ReverseDepIt = ReverseNonLocalDeps.find(RemInst); if (ReverseDepIt != ReverseNonLocalDeps.end()) { for (Instruction *I : ReverseDepIt->second) { assert(I != RemInst && "Already removed NonLocalDep info for RemInst"); PerInstNLInfo &INLD = NonLocalDepsMap[I]; // The information is now dirty! INLD.second = true; for (auto &Entry : INLD.first) { if (Entry.getResult().getInst() != RemInst) continue; // Convert to a dirty entry for the subsequent instruction. Entry.setResult(NewDirtyVal); if (Instruction *NextI = NewDirtyVal.getInst()) ReverseDepsToAdd.push_back(std::make_pair(NextI, I)); } } ReverseNonLocalDeps.erase(ReverseDepIt); // Add new reverse deps after scanning the set, to avoid invalidating 'Set' while (!ReverseDepsToAdd.empty()) { ReverseNonLocalDeps[ReverseDepsToAdd.back().first].insert( ReverseDepsToAdd.back().second); ReverseDepsToAdd.pop_back(); } } // If the instruction is in ReverseNonLocalPtrDeps then it appears as a // value in the NonLocalPointerDeps info. ReverseNonLocalPtrDepTy::iterator ReversePtrDepIt = ReverseNonLocalPtrDeps.find(RemInst); if (ReversePtrDepIt != ReverseNonLocalPtrDeps.end()) { SmallVector, 8> ReversePtrDepsToAdd; for (ValueIsLoadPair P : ReversePtrDepIt->second) { assert(P.getPointer() != RemInst && "Already removed NonLocalPointerDeps info for RemInst"); NonLocalDepInfo &NLPDI = NonLocalPointerDeps[P].NonLocalDeps; // The cache is not valid for any specific block anymore. NonLocalPointerDeps[P].Pair = BBSkipFirstBlockPair(); // Update any entries for RemInst to use the instruction after it. for (auto &Entry : NLPDI) { if (Entry.getResult().getInst() != RemInst) continue; // Convert to a dirty entry for the subsequent instruction. Entry.setResult(NewDirtyVal); if (Instruction *NewDirtyInst = NewDirtyVal.getInst()) ReversePtrDepsToAdd.push_back(std::make_pair(NewDirtyInst, P)); } // Re-sort the NonLocalDepInfo. Changing the dirty entry to its // subsequent value may invalidate the sortedness. llvm::sort(NLPDI); } ReverseNonLocalPtrDeps.erase(ReversePtrDepIt); while (!ReversePtrDepsToAdd.empty()) { ReverseNonLocalPtrDeps[ReversePtrDepsToAdd.back().first].insert( ReversePtrDepsToAdd.back().second); ReversePtrDepsToAdd.pop_back(); } } assert(!NonLocalDepsMap.count(RemInst) && "RemInst got reinserted?"); LLVM_DEBUG(verifyRemoved(RemInst)); } /// Verify that the specified instruction does not occur in our internal data /// structures. /// /// This function verifies by asserting in debug builds. void MemoryDependenceResults::verifyRemoved(Instruction *D) const { #ifndef NDEBUG for (const auto &DepKV : LocalDeps) { assert(DepKV.first != D && "Inst occurs in data structures"); assert(DepKV.second.getInst() != D && "Inst occurs in data structures"); } for (const auto &DepKV : NonLocalPointerDeps) { assert(DepKV.first.getPointer() != D && "Inst occurs in NLPD map key"); for (const auto &Entry : DepKV.second.NonLocalDeps) assert(Entry.getResult().getInst() != D && "Inst occurs as NLPD value"); } for (const auto &DepKV : NonLocalDepsMap) { assert(DepKV.first != D && "Inst occurs in data structures"); const PerInstNLInfo &INLD = DepKV.second; for (const auto &Entry : INLD.first) assert(Entry.getResult().getInst() != D && "Inst occurs in data structures"); } for (const auto &DepKV : ReverseLocalDeps) { assert(DepKV.first != D && "Inst occurs in data structures"); for (Instruction *Inst : DepKV.second) assert(Inst != D && "Inst occurs in data structures"); } for (const auto &DepKV : ReverseNonLocalDeps) { assert(DepKV.first != D && "Inst occurs in data structures"); for (Instruction *Inst : DepKV.second) assert(Inst != D && "Inst occurs in data structures"); } for (const auto &DepKV : ReverseNonLocalPtrDeps) { assert(DepKV.first != D && "Inst occurs in rev NLPD map"); for (ValueIsLoadPair P : DepKV.second) assert(P != ValueIsLoadPair(D, false) && P != ValueIsLoadPair(D, true) && "Inst occurs in ReverseNonLocalPtrDeps map"); } #endif } AnalysisKey MemoryDependenceAnalysis::Key; MemoryDependenceAnalysis::MemoryDependenceAnalysis() : DefaultBlockScanLimit(BlockScanLimit) {} MemoryDependenceResults MemoryDependenceAnalysis::run(Function &F, FunctionAnalysisManager &AM) { auto &AA = AM.getResult(F); auto &AC = AM.getResult(F); auto &TLI = AM.getResult(F); auto &DT = AM.getResult(F); return MemoryDependenceResults(AA, AC, TLI, DT, DefaultBlockScanLimit); } char MemoryDependenceWrapperPass::ID = 0; INITIALIZE_PASS_BEGIN(MemoryDependenceWrapperPass, "memdep", "Memory Dependence Analysis", false, true) INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass) INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) INITIALIZE_PASS_END(MemoryDependenceWrapperPass, "memdep", "Memory Dependence Analysis", false, true) MemoryDependenceWrapperPass::MemoryDependenceWrapperPass() : FunctionPass(ID) { initializeMemoryDependenceWrapperPassPass(*PassRegistry::getPassRegistry()); } MemoryDependenceWrapperPass::~MemoryDependenceWrapperPass() = default; void MemoryDependenceWrapperPass::releaseMemory() { MemDep.reset(); } void MemoryDependenceWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const { AU.setPreservesAll(); AU.addRequired(); AU.addRequired(); AU.addRequiredTransitive(); AU.addRequiredTransitive(); } bool MemoryDependenceResults::invalidate(Function &F, const PreservedAnalyses &PA, FunctionAnalysisManager::Invalidator &Inv) { // Check whether our analysis is preserved. auto PAC = PA.getChecker(); if (!PAC.preserved() && !PAC.preservedSet>()) // If not, give up now. return true; // Check whether the analyses we depend on became invalid for any reason. if (Inv.invalidate(F, PA) || Inv.invalidate(F, PA) || Inv.invalidate(F, PA)) return true; // Otherwise this analysis result remains valid. return false; } unsigned MemoryDependenceResults::getDefaultBlockScanLimit() const { return DefaultBlockScanLimit; } bool MemoryDependenceWrapperPass::runOnFunction(Function &F) { auto &AA = getAnalysis().getAAResults(); auto &AC = getAnalysis().getAssumptionCache(F); auto &TLI = getAnalysis().getTLI(F); auto &DT = getAnalysis().getDomTree(); MemDep.emplace(AA, AC, TLI, DT, BlockScanLimit); return false; }