| //===- MemoryDependenceAnalysis.cpp - Mem Deps Implementation --*- C++ -*-===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // 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. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "memdep" |
| #include "llvm/Analysis/MemoryDependenceAnalysis.h" |
| #include "llvm/Constants.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/Function.h" |
| #include "llvm/Analysis/AliasAnalysis.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/Support/CFG.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Target/TargetData.h" |
| using namespace llvm; |
| |
| 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"); |
| char MemoryDependenceAnalysis::ID = 0; |
| |
| // Register this pass... |
| static RegisterPass<MemoryDependenceAnalysis> X("memdep", |
| "Memory Dependence Analysis", false, true); |
| |
| /// getAnalysisUsage - Does not modify anything. It uses Alias Analysis. |
| /// |
| void MemoryDependenceAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.setPreservesAll(); |
| AU.addRequiredTransitive<AliasAnalysis>(); |
| AU.addRequiredTransitive<TargetData>(); |
| } |
| |
| bool MemoryDependenceAnalysis::runOnFunction(Function &) { |
| AA = &getAnalysis<AliasAnalysis>(); |
| TD = &getAnalysis<TargetData>(); |
| return false; |
| } |
| |
| |
| /// getCallSiteDependencyFrom - Private helper for finding the local |
| /// dependencies of a call site. |
| MemDepResult MemoryDependenceAnalysis:: |
| getCallSiteDependencyFrom(CallSite CS, BasicBlock::iterator ScanIt, |
| BasicBlock *BB) { |
| // Walk backwards through the block, looking for dependencies |
| while (ScanIt != BB->begin()) { |
| Instruction *Inst = --ScanIt; |
| |
| // If this inst is a memory op, get the pointer it accessed |
| Value *Pointer = 0; |
| uint64_t PointerSize = 0; |
| if (StoreInst *S = dyn_cast<StoreInst>(Inst)) { |
| Pointer = S->getPointerOperand(); |
| PointerSize = TD->getTypeStoreSize(S->getOperand(0)->getType()); |
| } else if (VAArgInst *V = dyn_cast<VAArgInst>(Inst)) { |
| Pointer = V->getOperand(0); |
| PointerSize = TD->getTypeStoreSize(V->getType()); |
| } else if (FreeInst *F = dyn_cast<FreeInst>(Inst)) { |
| Pointer = F->getPointerOperand(); |
| |
| // FreeInsts erase the entire structure |
| PointerSize = ~0UL; |
| } else if (isa<CallInst>(Inst) || isa<InvokeInst>(Inst)) { |
| CallSite InstCS = CallSite::get(Inst); |
| // If these two calls do not interfere, look past it. |
| if (AA->getModRefInfo(CS, InstCS) == AliasAnalysis::NoModRef) |
| continue; |
| |
| // FIXME: If this is a ref/ref result, we should ignore it! |
| // X = strlen(P); |
| // Y = strlen(Q); |
| // Z = strlen(P); // Z = X |
| |
| // If they interfere, we generally return clobber. However, if they are |
| // calls to the same read-only functions we return Def. |
| if (!AA->onlyReadsMemory(CS) || CS.getCalledFunction() == 0 || |
| CS.getCalledFunction() != InstCS.getCalledFunction()) |
| return MemDepResult::getClobber(Inst); |
| return MemDepResult::getDef(Inst); |
| } else { |
| // Non-memory instruction. |
| continue; |
| } |
| |
| if (AA->getModRefInfo(CS, Pointer, PointerSize) != AliasAnalysis::NoModRef) |
| return MemDepResult::getClobber(Inst); |
| } |
| |
| // No dependence found. |
| return MemDepResult::getNonLocal(); |
| } |
| |
| /// getDependencyFrom - Return the instruction on which a memory operation |
| /// depends. |
| MemDepResult MemoryDependenceAnalysis:: |
| getDependencyFrom(Instruction *QueryInst, BasicBlock::iterator ScanIt, |
| BasicBlock *BB) { |
| // The first instruction in a block is always non-local. |
| if (ScanIt == BB->begin()) |
| return MemDepResult::getNonLocal(); |
| |
| // Get the pointer value for which dependence will be determined |
| Value *MemPtr = 0; |
| uint64_t MemSize = 0; |
| |
| if (StoreInst* S = dyn_cast<StoreInst>(QueryInst)) { |
| // If this is a volatile store, don't mess around with it. Just return the |
| // previous instruction as a clobber. |
| if (S->isVolatile()) |
| return MemDepResult::getClobber(--ScanIt); |
| |
| MemPtr = S->getPointerOperand(); |
| MemSize = TD->getTypeStoreSize(S->getOperand(0)->getType()); |
| } else if (LoadInst* LI = dyn_cast<LoadInst>(QueryInst)) { |
| // If this is a volatile load, don't mess around with it. Just return the |
| // previous instruction as a clobber. |
| if (S->isVolatile()) |
| return MemDepResult::getClobber(--ScanIt); |
| |
| MemPtr = LI->getPointerOperand(); |
| MemSize = TD->getTypeStoreSize(LI->getType()); |
| } else if (FreeInst* F = dyn_cast<FreeInst>(QueryInst)) { |
| MemPtr = F->getPointerOperand(); |
| // FreeInsts erase the entire structure, not just a field. |
| MemSize = ~0UL; |
| } else if (isa<CallInst>(QueryInst) || isa<InvokeInst>(QueryInst)) { |
| return getCallSiteDependencyFrom(CallSite::get(QueryInst), ScanIt, BB); |
| } else { |
| // Otherwise, this is a vaarg or non-memory instruction, just return a |
| // clobber dependency on the previous inst. |
| return MemDepResult::getClobber(--ScanIt); |
| } |
| |
| // Walk backwards through the basic block, looking for dependencies |
| while (ScanIt != BB->begin()) { |
| Instruction *Inst = --ScanIt; |
| |
| // 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. |
| if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) { |
| Value *Pointer = LI->getPointerOperand(); |
| uint64_t PointerSize = TD->getTypeStoreSize(LI->getType()); |
| |
| // If we found a pointer, check if it could be the same as our pointer. |
| AliasAnalysis::AliasResult R = |
| AA->alias(Pointer, PointerSize, MemPtr, MemSize); |
| if (R == AliasAnalysis::NoAlias) |
| continue; |
| |
| // May-alias loads don't depend on each other without a dependence. |
| if (isa<LoadInst>(QueryInst) && R == AliasAnalysis::MayAlias) |
| continue; |
| return MemDepResult::getDef(Inst); |
| } |
| |
| if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { |
| Value *Pointer = SI->getPointerOperand(); |
| uint64_t PointerSize = TD->getTypeStoreSize(SI->getOperand(0)->getType()); |
| |
| // If we found a pointer, check if it could be the same as our pointer. |
| AliasAnalysis::AliasResult R = |
| AA->alias(Pointer, PointerSize, MemPtr, MemSize); |
| |
| if (R == AliasAnalysis::NoAlias) |
| continue; |
| if (R == AliasAnalysis::MayAlias) |
| return MemDepResult::getClobber(Inst); |
| return MemDepResult::getDef(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. |
| if (AllocationInst *AI = dyn_cast<AllocationInst>(Inst)) { |
| Value *AccessPtr = MemPtr->getUnderlyingObject(); |
| |
| if (AccessPtr == AI || |
| AA->alias(AI, 1, AccessPtr, 1) == AliasAnalysis::MustAlias) |
| return MemDepResult::getDef(AI); |
| continue; |
| } |
| |
| // See if this instruction (e.g. a call or vaarg) mod/ref's the pointer. |
| if (AA->getModRefInfo(Inst, MemPtr, MemSize) == AliasAnalysis::NoModRef) |
| continue; |
| |
| // Otherwise, there is a dependence. |
| return MemDepResult::getClobber(Inst); |
| } |
| |
| // If we found nothing, return the non-local flag. |
| return MemDepResult::getNonLocal(); |
| } |
| |
| /// getDependency - Return the instruction on which a memory operation |
| /// depends. |
| MemDepResult MemoryDependenceAnalysis::getDependency(Instruction *QueryInst) { |
| 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; |
| |
| SmallPtrSet<Instruction*, 4> &InstMap = ReverseLocalDeps[Inst]; |
| InstMap.erase(QueryInst); |
| if (InstMap.empty()) |
| ReverseLocalDeps.erase(Inst); |
| } |
| |
| // Do the scan. |
| LocalCache = getDependencyFrom(QueryInst, ScanPos, QueryInst->getParent()); |
| |
| // Remember the result! |
| if (Instruction *I = LocalCache.getInst()) |
| ReverseLocalDeps[I].insert(QueryInst); |
| |
| return LocalCache; |
| } |
| |
| /// getNonLocalDependency - Perform a full dependency query for the |
| /// specified instruction, returning the set of blocks that the value is |
| /// potentially live across. The returned set of results will include a |
| /// "NonLocal" result for all blocks where the value is live across. |
| /// |
| /// This method assumes the instruction returns a "nonlocal" dependency |
| /// within its own block. |
| /// |
| const MemoryDependenceAnalysis::NonLocalDepInfo & |
| MemoryDependenceAnalysis::getNonLocalDependency(Instruction *QueryInst) { |
| assert(getDependency(QueryInst).isNonLocal() && |
| "getNonLocalDependency should only be used on insts with non-local deps!"); |
| PerInstNLInfo &CacheP = NonLocalDeps[QueryInst]; |
| |
| NonLocalDepInfo &Cache = CacheP.first; |
| |
| /// DirtyBlocks - 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<BasicBlock*, 32> 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 (NonLocalDepInfo::iterator I = Cache.begin(), E = Cache.end(); |
| I != E; ++I) |
| if (I->second.isDirty()) |
| DirtyBlocks.push_back(I->first); |
| |
| // Sort the cache so that we can do fast binary search lookups below. |
| std::sort(Cache.begin(), Cache.end()); |
| |
| ++NumCacheDirtyNonLocal; |
| //cerr << "CACHED CASE: " << DirtyBlocks.size() << " dirty: " |
| // << Cache.size() << " cached: " << *QueryInst; |
| } else { |
| // Seed DirtyBlocks with each of the preds of QueryInst's block. |
| BasicBlock *QueryBB = QueryInst->getParent(); |
| DirtyBlocks.append(pred_begin(QueryBB), pred_end(QueryBB)); |
| NumUncacheNonLocal++; |
| } |
| |
| // Visited checked first, vector in sorted order. |
| SmallPtrSet<BasicBlock*, 64> Visited; |
| |
| unsigned NumSortedEntries = Cache.size(); |
| |
| // Iterate while we still have blocks to update. |
| while (!DirtyBlocks.empty()) { |
| BasicBlock *DirtyBB = DirtyBlocks.back(); |
| DirtyBlocks.pop_back(); |
| |
| // Already processed this block? |
| if (!Visited.insert(DirtyBB)) |
| continue; |
| |
| // 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, |
| std::make_pair(DirtyBB, MemDepResult())); |
| if (Entry != Cache.begin() && (&*Entry)[-1].first == DirtyBB) |
| --Entry; |
| |
| MemDepResult *ExistingResult = 0; |
| if (Entry != Cache.begin()+NumSortedEntries && |
| Entry->first == DirtyBB) { |
| // If we already have an entry, and if it isn't already dirty, the block |
| // is done. |
| if (!Entry->second.isDirty()) |
| continue; |
| |
| // Otherwise, remember this slot so we can update the value. |
| ExistingResult = &Entry->second; |
| } |
| |
| // 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->getInst()) { |
| ScanPos = Inst; |
| |
| // We're removing QueryInst's use of Inst. |
| SmallPtrSet<Instruction*, 4> &InstMap = ReverseNonLocalDeps[Inst]; |
| InstMap.erase(QueryInst); |
| if (InstMap.empty()) ReverseNonLocalDeps.erase(Inst); |
| } |
| } |
| |
| // Find out if this block has a local dependency for QueryInst. |
| MemDepResult Dep = getDependencyFrom(QueryInst, ScanPos, DirtyBB); |
| |
| // If we had a dirty entry for the block, update it. Otherwise, just add |
| // a new entry. |
| if (ExistingResult) |
| *ExistingResult = Dep; |
| else |
| Cache.push_back(std::make_pair(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(QueryInst); |
| } else { |
| |
| // If the block *is* completely transparent to the load, we need to check |
| // the predecessors of this block. Add them to our worklist. |
| DirtyBlocks.append(pred_begin(DirtyBB), pred_end(DirtyBB)); |
| } |
| } |
| |
| return Cache; |
| } |
| |
| /// removeInstruction - Remove an instruction from the dependence analysis, |
| /// updating the dependence of instructions that previously depended on it. |
| /// This method attempts to keep the cache coherent using the reverse map. |
| void MemoryDependenceAnalysis::removeInstruction(Instruction *RemInst) { |
| // Walk through the Non-local dependencies, removing this one as the value |
| // for any cached queries. |
| NonLocalDepMapType::iterator NLDI = NonLocalDeps.find(RemInst); |
| if (NLDI != NonLocalDeps.end()) { |
| NonLocalDepInfo &BlockMap = NLDI->second.first; |
| for (NonLocalDepInfo::iterator DI = BlockMap.begin(), DE = BlockMap.end(); |
| DI != DE; ++DI) |
| if (Instruction *Inst = DI->second.getInst()) |
| ReverseNonLocalDeps[Inst].erase(RemInst); |
| NonLocalDeps.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()) { |
| SmallPtrSet<Instruction*, 4> &RLD = ReverseLocalDeps[Inst]; |
| RLD.erase(RemInst); |
| if (RLD.empty()) |
| ReverseLocalDeps.erase(Inst); |
| } |
| |
| // Remove this local dependency info. |
| LocalDeps.erase(LocalDepEntry); |
| } |
| |
| // Loop over all of the things that depend on the instruction we're removing. |
| // |
| SmallVector<std::pair<Instruction*, Instruction*>, 8> ReverseDepsToAdd; |
| |
| ReverseDepMapType::iterator ReverseDepIt = ReverseLocalDeps.find(RemInst); |
| if (ReverseDepIt != ReverseLocalDeps.end()) { |
| SmallPtrSet<Instruction*, 4> &ReverseDeps = ReverseDepIt->second; |
| // RemInst can't be the terminator if it has stuff depending on it. |
| assert(!ReverseDeps.empty() && !isa<TerminatorInst>(RemInst) && |
| "Nothing can locally depend on a terminator"); |
| |
| // Anything that was locally dependent on RemInst is now going to be |
| // dependent on the instruction after RemInst. It will have the dirty flag |
| // set so it will rescan. This saves having to scan the entire block to get |
| // to this point. |
| Instruction *NewDepInst = next(BasicBlock::iterator(RemInst)); |
| |
| for (SmallPtrSet<Instruction*, 4>::iterator I = ReverseDeps.begin(), |
| E = ReverseDeps.end(); I != E; ++I) { |
| Instruction *InstDependingOnRemInst = *I; |
| assert(InstDependingOnRemInst != RemInst && |
| "Already removed our local dep info"); |
| |
| LocalDeps[InstDependingOnRemInst] = MemDepResult::getDirty(NewDepInst); |
| |
| // Make sure to remember that new things depend on NewDepInst. |
| ReverseDepsToAdd.push_back(std::make_pair(NewDepInst, |
| 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()) { |
| SmallPtrSet<Instruction*, 4>& set = ReverseDepIt->second; |
| for (SmallPtrSet<Instruction*, 4>::iterator I = set.begin(), E = set.end(); |
| I != E; ++I) { |
| assert(*I != RemInst && "Already removed NonLocalDep info for RemInst"); |
| |
| PerInstNLInfo &INLD = NonLocalDeps[*I]; |
| // The information is now dirty! |
| INLD.second = true; |
| |
| for (NonLocalDepInfo::iterator DI = INLD.first.begin(), |
| DE = INLD.first.end(); DI != DE; ++DI) { |
| if (DI->second.getInst() != RemInst) continue; |
| |
| // Convert to a dirty entry for the subsequent instruction. |
| Instruction *NextI = 0; |
| if (!RemInst->isTerminator()) { |
| NextI = next(BasicBlock::iterator(RemInst)); |
| ReverseDepsToAdd.push_back(std::make_pair(NextI, *I)); |
| } |
| DI->second = MemDepResult::getDirty(NextI); |
| } |
| } |
| |
| 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(); |
| } |
| } |
| |
| assert(!NonLocalDeps.count(RemInst) && "RemInst got reinserted?"); |
| AA->deleteValue(RemInst); |
| DEBUG(verifyRemoved(RemInst)); |
| } |
| |
| /// verifyRemoved - Verify that the specified instruction does not occur |
| /// in our internal data structures. |
| void MemoryDependenceAnalysis::verifyRemoved(Instruction *D) const { |
| for (LocalDepMapType::const_iterator I = LocalDeps.begin(), |
| E = LocalDeps.end(); I != E; ++I) { |
| assert(I->first != D && "Inst occurs in data structures"); |
| assert(I->second.getInst() != D && |
| "Inst occurs in data structures"); |
| } |
| |
| for (NonLocalDepMapType::const_iterator I = NonLocalDeps.begin(), |
| E = NonLocalDeps.end(); I != E; ++I) { |
| assert(I->first != D && "Inst occurs in data structures"); |
| const PerInstNLInfo &INLD = I->second; |
| for (NonLocalDepInfo::const_iterator II = INLD.first.begin(), |
| EE = INLD.first.end(); II != EE; ++II) |
| assert(II->second.getInst() != D && "Inst occurs in data structures"); |
| } |
| |
| for (ReverseDepMapType::const_iterator I = ReverseLocalDeps.begin(), |
| E = ReverseLocalDeps.end(); I != E; ++I) { |
| assert(I->first != D && "Inst occurs in data structures"); |
| for (SmallPtrSet<Instruction*, 4>::const_iterator II = I->second.begin(), |
| EE = I->second.end(); II != EE; ++II) |
| assert(*II != D && "Inst occurs in data structures"); |
| } |
| |
| for (ReverseDepMapType::const_iterator I = ReverseNonLocalDeps.begin(), |
| E = ReverseNonLocalDeps.end(); |
| I != E; ++I) { |
| assert(I->first != D && "Inst occurs in data structures"); |
| for (SmallPtrSet<Instruction*, 4>::const_iterator II = I->second.begin(), |
| EE = I->second.end(); II != EE; ++II) |
| assert(*II != D && "Inst occurs in data structures"); |
| } |
| } |