//===- MemoryDependenceAnalysis.cpp - Mem Deps Implementation -------------===// // // 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. // //===----------------------------------------------------------------------===// #include "llvm/Analysis/MemoryDependenceAnalysis.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/Statistic.h" #include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/AssumptionCache.h" #include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/MemoryBuiltins.h" #include "llvm/Analysis/PHITransAddr.h" #include "llvm/Analysis/OrderedBasicBlock.h" #include "llvm/Analysis/ValueTracking.h" #include "llvm/Analysis/TargetLibraryInfo.h" #include "llvm/IR/DataLayout.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/Function.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/LLVMContext.h" #include "llvm/IR/PredIteratorCache.h" #include "llvm/Support/Debug.h" 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(1000), cl::desc("The number of blocks to scan during memory " "dependency analysis (default = 1000)")); // Limit on the number of memdep results to process. static const unsigned int NumResultsLimit = 100; char MemoryDependenceAnalysis::ID = 0; // Register this pass... INITIALIZE_PASS_BEGIN(MemoryDependenceAnalysis, "memdep", "Memory Dependence Analysis", false, true) INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass) INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) INITIALIZE_PASS_END(MemoryDependenceAnalysis, "memdep", "Memory Dependence Analysis", false, true) MemoryDependenceAnalysis::MemoryDependenceAnalysis() : FunctionPass(ID) { initializeMemoryDependenceAnalysisPass(*PassRegistry::getPassRegistry()); } MemoryDependenceAnalysis::~MemoryDependenceAnalysis() { } /// Clean up memory in between runs void MemoryDependenceAnalysis::releaseMemory() { LocalDeps.clear(); NonLocalDeps.clear(); NonLocalPointerDeps.clear(); ReverseLocalDeps.clear(); ReverseNonLocalDeps.clear(); ReverseNonLocalPtrDeps.clear(); PredCache.clear(); } /// getAnalysisUsage - Does not modify anything. It uses Alias Analysis. /// void MemoryDependenceAnalysis::getAnalysisUsage(AnalysisUsage &AU) const { AU.setPreservesAll(); AU.addRequired(); AU.addRequiredTransitive(); AU.addRequiredTransitive(); } bool MemoryDependenceAnalysis::runOnFunction(Function &F) { AA = &getAnalysis().getAAResults(); AC = &getAnalysis().getAssumptionCache(F); DominatorTreeWrapperPass *DTWP = getAnalysisIfAvailable(); DT = DTWP ? &DTWP->getDomTree() : nullptr; TLI = &getAnalysis().getTLI(); return false; } /// RemoveFromReverseMap - 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); } /// GetLocation - If the given instruction references a specific memory /// location, fill in Loc with the details, otherwise set Loc.Ptr to null. /// Return 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 MRI_Ref; } if (LI->getOrdering() == Monotonic) { Loc = MemoryLocation::get(LI); return MRI_ModRef; } Loc = MemoryLocation(); return MRI_ModRef; } if (const StoreInst *SI = dyn_cast(Inst)) { if (SI->isUnordered()) { Loc = MemoryLocation::get(SI); return MRI_Mod; } if (SI->getOrdering() == Monotonic) { Loc = MemoryLocation::get(SI); return MRI_ModRef; } Loc = MemoryLocation(); return MRI_ModRef; } if (const VAArgInst *V = dyn_cast(Inst)) { Loc = MemoryLocation::get(V); return MRI_ModRef; } if (const CallInst *CI = isFreeCall(Inst, &TLI)) { // calls to free() deallocate the entire structure Loc = MemoryLocation(CI->getArgOperand(0)); return MRI_Mod; } if (const IntrinsicInst *II = dyn_cast(Inst)) { AAMDNodes AAInfo; switch (II->getIntrinsicID()) { case Intrinsic::lifetime_start: case Intrinsic::lifetime_end: case Intrinsic::invariant_start: II->getAAMetadata(AAInfo); Loc = MemoryLocation( II->getArgOperand(1), cast(II->getArgOperand(0))->getZExtValue(), AAInfo); // These intrinsics don't really modify the memory, but returning Mod // will allow them to be handled conservatively. return MRI_Mod; case Intrinsic::invariant_end: II->getAAMetadata(AAInfo); Loc = MemoryLocation( II->getArgOperand(2), cast(II->getArgOperand(1))->getZExtValue(), AAInfo); // These intrinsics don't really modify the memory, but returning Mod // will allow them to be handled conservatively. return MRI_Mod; default: break; } } // Otherwise, just do the coarse-grained thing that always works. if (Inst->mayWriteToMemory()) return MRI_ModRef; if (Inst->mayReadFromMemory()) return MRI_Ref; return MRI_NoModRef; } /// getCallSiteDependencyFrom - Private helper for finding the local /// dependencies of a call site. MemDepResult MemoryDependenceAnalysis:: getCallSiteDependencyFrom(CallSite CS, bool isReadOnlyCall, BasicBlock::iterator ScanIt, BasicBlock *BB) { unsigned Limit = BlockScanLimit; // Walk backwards through the block, looking for dependencies while (ScanIt != BB->begin()) { // 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(); Instruction *Inst = &*--ScanIt; // 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 (AA->getModRefInfo(CS, Loc) != MRI_NoModRef) return MemDepResult::getClobber(Inst); continue; } if (auto InstCS = CallSite(Inst)) { // Debug intrinsics don't cause dependences. if (isa(Inst)) continue; // If these two calls do not interfere, look past it. switch (AA->getModRefInfo(CS, InstCS)) { case MRI_NoModRef: // If the two calls are the same, return InstCS as a Def, so that // CS can be found redundant and eliminated. if (isReadOnlyCall && !(MR & MRI_Mod) && CS.getInstruction()->isIdenticalToWhenDefined(Inst)) return MemDepResult::getDef(Inst); // Otherwise if the two calls don't interact (e.g. InstCS is readnone) // keep scanning. continue; default: 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 (MR != MRI_NoModRef) 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(); } /// isLoadLoadClobberIfExtendedToFullWidth - Return true if LI is a load that /// would fully overlap MemLoc if done as a wider legal integer load. /// /// MemLocBase, MemLocOffset are lazily computed here the first time the /// base/offs of memloc is needed. static bool isLoadLoadClobberIfExtendedToFullWidth(const MemoryLocation &MemLoc, const Value *&MemLocBase, int64_t &MemLocOffs, const LoadInst *LI) { const DataLayout &DL = LI->getModule()->getDataLayout(); // If we haven't already computed the base/offset of MemLoc, do so now. if (!MemLocBase) MemLocBase = GetPointerBaseWithConstantOffset(MemLoc.Ptr, MemLocOffs, DL); unsigned Size = MemoryDependenceAnalysis::getLoadLoadClobberFullWidthSize( MemLocBase, MemLocOffs, MemLoc.Size, LI); return Size != 0; } /// getLoadLoadClobberFullWidthSize - This is a little bit of analysis that /// looks at a memory location for a load (specified by MemLocBase, Offs, /// and Size) and compares it against a load. If the specified load could /// be safely widened to a larger integer load that is 1) still efficient, /// 2) safe for the target, and 3) would provide the specified memory /// location value, then this function returns the size in bytes of the /// load width to use. If not, this returns zero. unsigned MemoryDependenceAnalysis::getLoadLoadClobberFullWidthSize( const Value *MemLocBase, int64_t MemLocOffs, unsigned MemLocSize, const LoadInst *LI) { // We can only extend simple integer loads. if (!isa(LI->getType()) || !LI->isSimple()) return 0; // Load widening is hostile to ThreadSanitizer: it may cause false positives // or make the reports more cryptic (access sizes are wrong). if (LI->getParent()->getParent()->hasFnAttribute(Attribute::SanitizeThread)) return 0; const DataLayout &DL = LI->getModule()->getDataLayout(); // Get the base of this load. int64_t LIOffs = 0; const Value *LIBase = GetPointerBaseWithConstantOffset(LI->getPointerOperand(), LIOffs, DL); // If the two pointers are not based on the same pointer, we can't tell that // they are related. if (LIBase != MemLocBase) return 0; // Okay, the two values are based on the same pointer, but returned as // no-alias. This happens when we have things like two byte loads at "P+1" // and "P+3". Check to see if increasing the size of the "LI" load up to its // alignment (or the largest native integer type) will allow us to load all // the bits required by MemLoc. // If MemLoc is before LI, then no widening of LI will help us out. if (MemLocOffs < LIOffs) return 0; // Get the alignment of the load in bytes. We assume that it is safe to load // any legal integer up to this size without a problem. For example, if we're // looking at an i8 load on x86-32 that is known 1024 byte aligned, we can // widen it up to an i32 load. If it is known 2-byte aligned, we can widen it // to i16. unsigned LoadAlign = LI->getAlignment(); int64_t MemLocEnd = MemLocOffs+MemLocSize; // If no amount of rounding up will let MemLoc fit into LI, then bail out. if (LIOffs+LoadAlign < MemLocEnd) return 0; // This is the size of the load to try. Start with the next larger power of // two. unsigned NewLoadByteSize = LI->getType()->getPrimitiveSizeInBits()/8U; NewLoadByteSize = NextPowerOf2(NewLoadByteSize); while (1) { // If this load size is bigger than our known alignment or would not fit // into a native integer register, then we fail. if (NewLoadByteSize > LoadAlign || !DL.fitsInLegalInteger(NewLoadByteSize*8)) return 0; if (LIOffs + NewLoadByteSize > MemLocEnd && LI->getParent()->getParent()->hasFnAttribute( Attribute::SanitizeAddress)) // We will be reading past the location accessed by the original program. // While this is safe in a regular build, Address Safety analysis tools // may start reporting false warnings. So, don't do widening. return 0; // If a load of this width would include all of MemLoc, then we succeed. if (LIOffs+NewLoadByteSize >= MemLocEnd) return NewLoadByteSize; NewLoadByteSize <<= 1; } } static bool isVolatile(Instruction *Inst) { if (LoadInst *LI = dyn_cast(Inst)) return LI->isVolatile(); else if (StoreInst *SI = dyn_cast(Inst)) return SI->isVolatile(); else if (AtomicCmpXchgInst *AI = dyn_cast(Inst)) return AI->isVolatile(); return false; } /// getPointerDependencyFrom - Return the instruction on which a memory /// location depends. If isLoad is true, this routine ignores may-aliases with /// read-only operations. If isLoad is false, this routine ignores may-aliases /// with reads from read-only locations. If possible, pass the query /// instruction as well; this function may take advantage of the metadata /// annotated to the query instruction to refine the result. MemDepResult MemoryDependenceAnalysis::getPointerDependencyFrom( const MemoryLocation &MemLoc, bool isLoad, BasicBlock::iterator ScanIt, BasicBlock *BB, Instruction *QueryInst) { if (QueryInst != nullptr) { if (auto *LI = dyn_cast(QueryInst)) { MemDepResult invariantGroupDependency = getInvariantGroupPointerDependency(LI, BB); if (invariantGroupDependency.isDef()) return invariantGroupDependency; } } return getSimplePointerDependencyFrom(MemLoc, isLoad, ScanIt, BB, QueryInst); } MemDepResult MemoryDependenceAnalysis::getInvariantGroupPointerDependency(LoadInst *LI, BasicBlock *BB) { Value *LoadOperand = LI->getPointerOperand(); // It's is not safe to walk the use list of global value, because function // passes aren't allowed to look outside their functions. if (isa(LoadOperand)) return MemDepResult::getUnknown(); auto *InvariantGroupMD = LI->getMetadata(LLVMContext::MD_invariant_group); if (!InvariantGroupMD) return MemDepResult::getUnknown(); MemDepResult Result = MemDepResult::getUnknown(); llvm::SmallSet Seen; // Queue to process all pointers that are equivalent to load operand. llvm::SmallVector LoadOperandsQueue; LoadOperandsQueue.push_back(LoadOperand); while (!LoadOperandsQueue.empty()) { Value *Ptr = LoadOperandsQueue.pop_back_val(); if (isa(Ptr)) continue; if (auto *BCI = dyn_cast(Ptr)) { if (!Seen.count(BCI->getOperand(0))) { LoadOperandsQueue.push_back(BCI->getOperand(0)); Seen.insert(BCI->getOperand(0)); } } for (Use &Us : Ptr->uses()) { auto *U = dyn_cast(Us.getUser()); if (!U || U == LI || !DT->dominates(U, LI)) continue; if (auto *BCI = dyn_cast(U)) { if (!Seen.count(BCI)) { LoadOperandsQueue.push_back(BCI); Seen.insert(BCI); } 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)) && U->getParent() == BB && U->getMetadata(LLVMContext::MD_invariant_group) == InvariantGroupMD) return MemDepResult::getDef(U); } } return Result; } MemDepResult MemoryDependenceAnalysis::getSimplePointerDependencyFrom( const MemoryLocation &MemLoc, bool isLoad, BasicBlock::iterator ScanIt, BasicBlock *BB, Instruction *QueryInst) { const Value *MemLocBase = nullptr; int64_t MemLocOffset = 0; unsigned Limit = BlockScanLimit; bool isInvariantLoad = false; // We must be careful with atomic accesses, as they may allow another thread // to touch this location, cloberring 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 progam racy). // The paper mentioned above shows that the same property is respected // by every program that can detect any optimisation 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) { LoadInst *LI = dyn_cast(QueryInst); if (LI && LI->getMetadata(LLVMContext::MD_invariant_load) != nullptr) isInvariantLoad = true; } const DataLayout &DL = BB->getModule()->getDataLayout(); // Create a numbered basic block to lazily compute and cache instruction // positions inside a BB. This is used to provide fast queries for relative // position between two instructions in a BB and can be used by // AliasAnalysis::callCapturesBefore. OrderedBasicBlock OBB(BB); // 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. if (II->getIntrinsicID() == 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). if (AA->isMustAlias(MemoryLocation(II->getArgOperand(1)), MemLoc)) return MemDepResult::getDef(II); continue; } } // 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 (isVolatile(QueryInst)) // 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() && LI->getOrdering() > Unordered) { if (!QueryInst) return MemDepResult::getClobber(LI); if (LI->getOrdering() != Monotonic) return MemDepResult::getClobber(LI); if (auto *QueryLI = dyn_cast(QueryInst)) { if (!QueryLI->isSimple()) return MemDepResult::getClobber(LI); } else if (auto *QuerySI = dyn_cast(QueryInst)) { if (!QuerySI->isSimple()) return MemDepResult::getClobber(LI); } else if (QueryInst->mayReadOrWriteMemory()) { 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 = AA->alias(LoadLoc, MemLoc); if (isLoad) { if (R == NoAlias) { // If this is an over-aligned integer load (for example, // "load i8* %P, align 4") see if it would obviously overlap with the // queried location if widened to a larger load (e.g. if the queried // location is 1 byte at P+1). If so, return it as a load/load // clobber result, allowing the client to decide to widen the load if // it wants to. if (IntegerType *ITy = dyn_cast(LI->getType())) { if (LI->getAlignment() * 8 > ITy->getPrimitiveSizeInBits() && isLoadLoadClobberIfExtendedToFullWidth(MemLoc, MemLocBase, MemLocOffset, LI)) return MemDepResult::getClobber(Inst); } continue; } // Must aliased loads are defs of each other. if (R == MustAlias) return MemDepResult::getDef(Inst); #if 0 // FIXME: Temporarily disabled. GVN is cleverly rewriting loads // in terms of clobbering loads, but since it does this by looking // at the clobbering load directly, it doesn't know about any // phi translation that may have happened along the way. // If we have a partial alias, then return this as a clobber for the // client to handle. if (R == PartialAlias) return MemDepResult::getClobber(Inst); #endif // Random may-alias loads don't depend on each other without a // dependence. continue; } // Stores don't depend on other no-aliased accesses. if (R == NoAlias) continue; // Stores don't alias loads from read-only memory. if (AA->pointsToConstantMemory(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()) { if (!QueryInst) return MemDepResult::getClobber(SI); if (SI->getOrdering() != Monotonic) return MemDepResult::getClobber(SI); if (auto *QueryLI = dyn_cast(QueryInst)) { if (!QueryLI->isSimple()) return MemDepResult::getClobber(SI); } else if (auto *QuerySI = dyn_cast(QueryInst)) { if (!QuerySI->isSimple()) return MemDepResult::getClobber(SI); } else if (QueryInst->mayReadOrWriteMemory()) { return MemDepResult::getClobber(SI); } } // FIXME: this is overly conservative. // 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()) 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 (AA->getModRefInfo(SI, MemLoc) == MRI_NoModRef) 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. MemoryLocation StoreLoc = MemoryLocation::get(SI); // If we found a pointer, check if it could be the same as our pointer. AliasResult R = AA->alias(StoreLoc, MemLoc); if (R == NoAlias) continue; if (R == MustAlias) return MemDepResult::getDef(Inst); if (isInvariantLoad) 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: Only determine this to be a malloc if Inst is the malloc call, not // a subsequent bitcast of the malloc call result. There can be stores to // the malloced memory between the malloc call and its bitcast uses, and we // need to continue scanning until the malloc call. if (isa(Inst) || isNoAliasFn(Inst, TLI)) { const Value *AccessPtr = GetUnderlyingObject(MemLoc.Ptr, DL); if (AccessPtr == Inst || AA->isMustAlias(Inst, AccessPtr)) return MemDepResult::getDef(Inst); if (isInvariantLoad) continue; // Be conservative if the accessed pointer may alias the allocation - // fallback to the generic handling below. if ((AA->alias(Inst, AccessPtr) == NoAlias) && // If the allocation is not aliased and does not read memory (like // strdup), it is safe to ignore. (isa(Inst) || isMallocLikeFn(Inst, TLI) || isCallocLikeFn(Inst, TLI))) continue; } if (isInvariantLoad) continue; // See if this instruction (e.g. a call or vaarg) mod/ref's the pointer. ModRefInfo MR = AA->getModRefInfo(Inst, MemLoc); // If necessary, perform additional analysis. if (MR == MRI_ModRef) MR = AA->callCapturesBefore(Inst, MemLoc, DT, &OBB); switch (MR) { case MRI_NoModRef: // If the call has no effect on the queried pointer, just ignore it. continue; case MRI_Mod: return MemDepResult::getClobber(Inst); case MRI_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; 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(); } /// 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; 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 = !(MR & MRI_Mod); if (IntrinsicInst *II = dyn_cast(QueryInst)) isLoad |= II->getIntrinsicID() == Intrinsic::lifetime_start; LocalCache = getPointerDependencyFrom( MemLoc, isLoad, ScanPos->getIterator(), QueryParent, QueryInst); } else if (isa(QueryInst) || isa(QueryInst)) { CallSite QueryCS(QueryInst); bool isReadOnly = AA->onlyReadsMemory(QueryCS); LocalCache = getCallSiteDependencyFrom( QueryCS, 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 /// AssertSorted - This method is used when -debug is specified to verify that /// cache arrays are properly kept sorted. static void AssertSorted(MemoryDependenceAnalysis::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 /// getNonLocalCallDependency - Perform a full dependency query for the /// specified call, 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. /// /// This returns a reference to an internal data structure that may be /// invalidated on the next non-local query or when an instruction is /// removed. Clients must copy this data if they want it around longer than /// that. const MemoryDependenceAnalysis::NonLocalDepInfo & MemoryDependenceAnalysis::getNonLocalCallDependency(CallSite QueryCS) { assert(getDependency(QueryCS.getInstruction()).isNonLocal() && "getNonLocalCallDependency should only be used on calls with non-local deps!"); PerInstNLInfo &CacheP = NonLocalDeps[QueryCS.getInstruction()]; 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 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->getResult().isDirty()) DirtyBlocks.push_back(I->getBB()); // 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 = QueryCS.getInstruction()->getParent(); for (BasicBlock *Pred : PredCache.get(QueryBB)) DirtyBlocks.push_back(Pred); ++NumUncacheNonLocal; } // isReadonlyCall - If this is a read-only call, we can be more aggressive. bool isReadonlyCall = AA->onlyReadsMemory(QueryCS); SmallPtrSet Visited; unsigned NumSortedEntries = Cache.size(); DEBUG(AssertSorted(Cache)); // 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).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. 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, QueryCS.getInstruction()); } } // Find out if this block has a local dependency for QueryInst. MemDepResult Dep; if (ScanPos != DirtyBB->begin()) { Dep = getCallSiteDependencyFrom(QueryCS, 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(QueryCS.getInstruction()); } else { // If the block *is* completely transparent to the load, we need to check // the predecessors of this block. Add them to our worklist. for (BasicBlock *Pred : PredCache.get(DirtyBB)) DirtyBlocks.push_back(Pred); } } return Cache; } /// getNonLocalPointerDependency - Perform a full dependency query for an /// access to the specified (non-volatile) memory location, returning the /// set of instructions that either define or clobber the value. /// /// This method assumes the pointer has a "NonLocal" dependency within its /// own block. /// void MemoryDependenceAnalysis:: 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(); // 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 (isVolatile(QueryInst) || 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))); } /// GetNonLocalInfoForBlock - 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 MemoryDependenceAnalysis::GetNonLocalInfoForBlock( Instruction *QueryInst, const MemoryLocation &Loc, bool isLoad, BasicBlock *BB, NonLocalDepInfo *Cache, unsigned NumSortedEntries) { // 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; // 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); // 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.isDef() && !Dep.isClobber()) 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; } /// SortNonLocalDepInfoCache - 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(MemoryDependenceAnalysis::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(); MemoryDependenceAnalysis::NonLocalDepInfo::iterator Entry = std::upper_bound(Cache.begin(), Cache.end()-1, Val); Cache.insert(Entry, Val); // FALL THROUGH. } 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(); MemoryDependenceAnalysis::NonLocalDepInfo::iterator Entry = std::upper_bound(Cache.begin(), Cache.end(), Val); Cache.insert(Entry, Val); } break; default: // Added many values, do a full scale sort. std::sort(Cache.begin(), Cache.end()); break; } } /// getNonLocalPointerDepFromBB - 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 false on success, or true 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 MemoryDependenceAnalysis::getNonLocalPointerDepFromBB( Instruction *QueryInst, const PHITransAddr &Pointer, const MemoryLocation &Loc, bool isLoad, BasicBlock *StartBB, SmallVectorImpl &Result, DenseMap &Visited, bool SkipFirstBlock) { // 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; // 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. if (!Pair.second) { if (CacheInfo->Size < Loc.Size) { // 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 (NonLocalDepInfo::iterator DI = CacheInfo->NonLocalDeps.begin(), DE = CacheInfo->NonLocalDeps.end(); DI != DE; ++DI) if (Instruction *Inst = DI->getResult().getInst()) RemoveFromReverseMap(ReverseNonLocalPtrDeps, Inst, CacheKey); CacheInfo->NonLocalDeps.clear(); } else if (CacheInfo->Size > Loc.Size) { // 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); } // 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 (NonLocalDepInfo::iterator DI = CacheInfo->NonLocalDeps.begin(), DE = CacheInfo->NonLocalDeps.end(); DI != DE; ++DI) if (Instruction *Inst = DI->getResult().getInst()) RemoveFromReverseMap(ReverseNonLocalPtrDeps, Inst, CacheKey); CacheInfo->NonLocalDeps.clear(); } if (Loc.AATags) return getNonLocalPointerDepFromBB(QueryInst, Pointer, Loc.getWithoutAATags(), isLoad, StartBB, Result, Visited, SkipFirstBlock); } } NonLocalDepInfo *Cache = &CacheInfo->NonLocalDeps; // If we have valid cached information for exactly the block we are // investigating, just return it with no recomputation. if (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 (NonLocalDepInfo::iterator I = Cache->begin(), E = Cache->end(); I != E; ++I) { DenseMap::iterator VI = Visited.find(I->getBB()); if (VI == Visited.end() || VI->second == Pointer.getAddr()) continue; // We have a pointer mismatch in a block. Just return clobber, 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 true; } } Value *Addr = Pointer.getAddr(); for (NonLocalDepInfo::iterator I = Cache->begin(), E = Cache->end(); I != E; ++I) { Visited.insert(std::make_pair(I->getBB(), Addr)); if (I->getResult().isNonLocal()) { continue; } if (!DT) { Result.push_back(NonLocalDepResult(I->getBB(), MemDepResult::getUnknown(), Addr)); } else if (DT->isReachableFromEntry(I->getBB())) { Result.push_back(NonLocalDepResult(I->getBB(), I->getResult(), Addr)); } } ++NumCacheCompleteNonLocalPtr; return false; } // 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, the result will be valid cache info, // otherwise it isn't. if (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; DEBUG(AssertSorted(*Cache)); 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) { Worklist.clear(); // 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 true; } // 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. DEBUG(AssertSorted(*Cache, NumSortedEntries)); MemDepResult Dep = GetNonLocalInfoForBlock(QueryInst, Loc, isLoad, BB, Cache, NumSortedEntries); // If we got a Def or Clobber, add this to the list of results. if (!Dep.isNonLocal()) { if (!DT) { Result.push_back(NonLocalDepResult(BB, MemDepResult::getUnknown(), Pointer.getAddr())); continue; } else 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; PredPointer.PHITranslateValue(BB, Pred, DT, /*MustDominate=*/false); Value *PredPtrVal = PredPointer.getAddr(); // 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 true; bool foundBlock = false; 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"); foundBlock = true; I.setResult(MemDepResult::getUnknown()); Result.push_back(NonLocalDepResult(I.getBB(), I.getResult(), Pointer.getAddr())); break; } (void)foundBlock; assert((foundBlock || GotWorklistLimit) && "Current block not in cache?"); } // Okay, we're done now. If we added new values to the cache, re-sort it. SortNonLocalDepInfoCache(*Cache, NumSortedEntries); DEBUG(AssertSorted(*Cache)); return false; } /// RemoveCachedNonLocalPointerDependencies - If P exists in /// CachedNonLocalPointerInfo, remove it. void MemoryDependenceAnalysis:: RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P) { 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 (unsigned i = 0, e = PInfo.size(); i != e; ++i) { Instruction *Target = PInfo[i].getResult().getInst(); if (!Target) continue; // Ignore non-local dep results. assert(Target->getParent() == PInfo[i].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); } /// invalidateCachedPointerInfo - This method is used to invalidate cached /// information about the specified pointer, because it may be too /// conservative in memdep. This is an optional call that can be used when /// the client detects an equivalence between the pointer and some other /// value and replaces the other value with ptr. This can make Ptr available /// in more places that cached info does not necessarily keep. void MemoryDependenceAnalysis::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)); } /// invalidateCachedPredecessors - Clear the PredIteratorCache info. /// This needs to be done when the CFG changes, e.g., due to splitting /// critical edges. void MemoryDependenceAnalysis::invalidateCachedPredecessors() { PredCache.clear(); } /// 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->getResult().getInst()) RemoveFromReverseMap(ReverseNonLocalDeps, Inst, 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()) RemoveFromReverseMap(ReverseLocalDeps, Inst, RemInst); // Remove this local dependency info. LocalDeps.erase(LocalDepEntry); } // If we have any cached pointer dependencies on this instruction, remove // them. If the instruction has non-pointer type, then it can't be a pointer // base. // Remove it from both the load info and the store info. The instruction // can't be in either of these maps if it is non-pointer. if (RemInst->getType()->isPointerTy()) { RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair(RemInst, false)); RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair(RemInst, true)); } // 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() && !isa(RemInst) && "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 = 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->getResult().getInst() != RemInst) continue; // Convert to a dirty entry for the subsequent instruction. DI->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 (NonLocalDepInfo::iterator DI = NLPDI.begin(), DE = NLPDI.end(); DI != DE; ++DI) { if (DI->getResult().getInst() != RemInst) continue; // Convert to a dirty entry for the subsequent instruction. DI->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. std::sort(NLPDI.begin(), NLPDI.end()); } ReverseNonLocalPtrDeps.erase(ReversePtrDepIt); while (!ReversePtrDepsToAdd.empty()) { ReverseNonLocalPtrDeps[ReversePtrDepsToAdd.back().first] .insert(ReversePtrDepsToAdd.back().second); ReversePtrDepsToAdd.pop_back(); } } assert(!NonLocalDeps.count(RemInst) && "RemInst got reinserted?"); DEBUG(verifyRemoved(RemInst)); } /// verifyRemoved - Verify that the specified instruction does not occur /// in our internal data structures. This function verifies by asserting in /// debug builds. void MemoryDependenceAnalysis::verifyRemoved(Instruction *D) const { #ifndef NDEBUG 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 (CachedNonLocalPointerInfo::const_iterator I =NonLocalPointerDeps.begin(), E = NonLocalPointerDeps.end(); I != E; ++I) { assert(I->first.getPointer() != D && "Inst occurs in NLPD map key"); const NonLocalDepInfo &Val = I->second.NonLocalDeps; for (NonLocalDepInfo::const_iterator II = Val.begin(), E = Val.end(); II != E; ++II) assert(II->getResult().getInst() != D && "Inst occurs as NLPD value"); } 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->getResult().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 (Instruction *Inst : I->second) assert(Inst != 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 (Instruction *Inst : I->second) assert(Inst != D && "Inst occurs in data structures"); } for (ReverseNonLocalPtrDepTy::const_iterator I = ReverseNonLocalPtrDeps.begin(), E = ReverseNonLocalPtrDeps.end(); I != E; ++I) { assert(I->first != D && "Inst occurs in rev NLPD map"); for (ValueIsLoadPair P : I->second) assert(P != ValueIsLoadPair(D, false) && P != ValueIsLoadPair(D, true) && "Inst occurs in ReverseNonLocalPtrDeps map"); } #endif }