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Diffstat (limited to 'contrib/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp')
| -rw-r--r-- | contrib/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp | 1724 |
1 files changed, 1724 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp b/contrib/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp new file mode 100644 index 000000000000..e7415e623196 --- /dev/null +++ b/contrib/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp @@ -0,0 +1,1724 @@ +//===- 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/SmallSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/AssumptionCache.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/CallSite.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/Instruction.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/IR/PredIteratorCache.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 "llvm/Support/MathExtras.h" +#include <algorithm> +#include <cassert> +#include <iterator> + +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<unsigned> 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<unsigned> + 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; + +/// This is a helper function that removes Val from 'Inst's set in ReverseMap. +/// +/// If the set becomes empty, remove Inst's entry. +template <typename KeyTy> +static void +RemoveFromReverseMap(DenseMap<Instruction *, SmallPtrSet<KeyTy, 4>> &ReverseMap, + Instruction *Inst, KeyTy Val) { + typename DenseMap<Instruction *, SmallPtrSet<KeyTy, 4>>::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<LoadInst>(Inst)) { + if (LI->isUnordered()) { + Loc = MemoryLocation::get(LI); + return MRI_Ref; + } + if (LI->getOrdering() == AtomicOrdering::Monotonic) { + Loc = MemoryLocation::get(LI); + return MRI_ModRef; + } + Loc = MemoryLocation(); + return MRI_ModRef; + } + + if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) { + if (SI->isUnordered()) { + Loc = MemoryLocation::get(SI); + return MRI_Mod; + } + if (SI->getOrdering() == AtomicOrdering::Monotonic) { + Loc = MemoryLocation::get(SI); + return MRI_ModRef; + } + Loc = MemoryLocation(); + return MRI_ModRef; + } + + if (const VAArgInst *V = dyn_cast<VAArgInst>(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<IntrinsicInst>(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<ConstantInt>(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<ConstantInt>(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; +} + +/// Private helper for finding the local dependencies of a call site. +MemDepResult MemoryDependenceResults::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<DbgInfoIntrinsic>(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(); +} + +unsigned MemoryDependenceResults::getLoadLoadClobberFullWidthSize( + const Value *MemLocBase, int64_t MemLocOffs, unsigned MemLocSize, + const LoadInst *LI) { + // We can only extend simple integer loads. + if (!isa<IntegerType>(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 (true) { + // 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<LoadInst>(Inst)) + return LI->isVolatile(); + else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) + return SI->isVolatile(); + else if (AtomicCmpXchgInst *AI = dyn_cast<AtomicCmpXchgInst>(Inst)) + return AI->isVolatile(); + return false; +} + +MemDepResult MemoryDependenceResults::getPointerDependencyFrom( + const MemoryLocation &MemLoc, bool isLoad, BasicBlock::iterator ScanIt, + BasicBlock *BB, Instruction *QueryInst, unsigned *Limit) { + + if (QueryInst != nullptr) { + if (auto *LI = dyn_cast<LoadInst>(QueryInst)) { + MemDepResult invariantGroupDependency = + getInvariantGroupPointerDependency(LI, BB); + + if (invariantGroupDependency.isDef()) + return invariantGroupDependency; + } + } + return getSimplePointerDependencyFrom(MemLoc, isLoad, ScanIt, BB, QueryInst, + Limit); +} + +MemDepResult +MemoryDependenceResults::getInvariantGroupPointerDependency(LoadInst *LI, + BasicBlock *BB) { + + auto *InvariantGroupMD = LI->getMetadata(LLVMContext::MD_invariant_group); + if (!InvariantGroupMD) + 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<GlobalValue>(LoadOperand)) + return MemDepResult::getUnknown(); + + // Queue to process all pointers that are equivalent to load operand. + SmallVector<const Value *, 8> LoadOperandsQueue; + LoadOperandsQueue.push_back(LoadOperand); + while (!LoadOperandsQueue.empty()) { + const Value *Ptr = LoadOperandsQueue.pop_back_val(); + assert(Ptr && !isa<GlobalValue>(Ptr) && + "Null or GlobalValue should not be inserted"); + + for (const Use &Us : Ptr->uses()) { + auto *U = dyn_cast<Instruction>(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<BitCastInst>(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<GetElementPtrInst>(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<LoadInst>(U) || isa<StoreInst>(U)) && U->getParent() == BB && + U->getMetadata(LLVMContext::MD_invariant_group) == InvariantGroupMD) + return MemDepResult::getDef(U); + } + } + return MemDepResult::getUnknown(); +} + +MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom( + const MemoryLocation &MemLoc, bool isLoad, BasicBlock::iterator ScanIt, + BasicBlock *BB, Instruction *QueryInst, unsigned *Limit) { + bool isInvariantLoad = false; + + if (!Limit) { + unsigned DefaultLimit = BlockScanLimit; + return getSimplePointerDependencyFrom(MemLoc, isLoad, ScanIt, BB, QueryInst, + &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) { + LoadInst *LI = dyn_cast<LoadInst>(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); + + // Return "true" if and only if the instruction I is either a non-simple + // load or a non-simple store. + auto isNonSimpleLoadOrStore = [](Instruction *I) -> bool { + if (auto *LI = dyn_cast<LoadInst>(I)) + return !LI->isSimple(); + if (auto *SI = dyn_cast<StoreInst>(I)) + return !SI->isSimple(); + return false; + }; + + // Return "true" if I is not a load and not a store, but it does access + // memory. + auto isOtherMemAccess = [](Instruction *I) -> bool { + return !isa<LoadInst>(I) && !isa<StoreInst>(I) && I->mayReadOrWriteMemory(); + }; + + // Walk backwards through the basic block, looking for dependencies. + while (ScanIt != BB->begin()) { + Instruction *Inst = &*--ScanIt; + + if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) + // Debug intrinsics don't (and can't) cause dependencies. + if (isa<DbgInfoIntrinsic>(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<IntrinsicInst>(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<LoadInst>(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() && isStrongerThanUnordered(LI->getOrdering())) { + if (!QueryInst || isNonSimpleLoadOrStore(QueryInst) || + isOtherMemAccess(QueryInst)) + 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 = AA.alias(LoadLoc, MemLoc); + + if (isLoad) { + if (R == NoAlias) + 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<StoreInst>(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 || isNonSimpleLoadOrStore(QueryInst) || + isOtherMemAccess(QueryInst)) + return MemDepResult::getClobber(SI); + if (SI->getOrdering() != AtomicOrdering::Monotonic) + 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()) + if (!QueryInst || isNonSimpleLoadOrStore(QueryInst) || + isOtherMemAccess(QueryInst)) + 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 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<AllocaInst>(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; + + // 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 preceeding stores to delete and thus we + // can't bypass the fence if the query instruction is a store. + if (FenceInst *FI = dyn_cast<FenceInst>(Inst)) + if (isLoad && FI->getOrdering() == AtomicOrdering::Release) + 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(); +} + +MemDepResult MemoryDependenceResults::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 (auto *II = dyn_cast<IntrinsicInst>(QueryInst)) + isLoad |= II->getIntrinsicID() == Intrinsic::lifetime_start; + + LocalCache = getPointerDependencyFrom( + MemLoc, isLoad, ScanPos->getIterator(), QueryParent, QueryInst); + } else if (isa<CallInst>(QueryInst) || isa<InvokeInst>(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 +/// 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(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; + + // 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 (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. + 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<BasicBlock *, 32> 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; +} + +void MemoryDependenceResults::getNonLocalPointerDependency( + Instruction *QueryInst, SmallVectorImpl<NonLocalDepResult> &Result) { + const MemoryLocation Loc = MemoryLocation::get(QueryInst); + bool isLoad = isa<LoadInst>(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<LoadInst>(Inst)) { + return !LI->isUnordered(); + } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { + return !SI->isUnordered(); + } + return false; + }; + if (isVolatile(QueryInst) || isOrdered(QueryInst)) { + Result.push_back(NonLocalDepResult(FromBB, MemDepResult::getUnknown(), + const_cast<Value *>(Loc.Ptr))); + return; + } + const DataLayout &DL = FromBB->getModule()->getDataLayout(); + PHITransAddr Address(const_cast<Value *>(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<BasicBlock *, Value *> Visited; + if (getNonLocalPointerDepFromBB(QueryInst, Address, Loc, isLoad, FromBB, + Result, Visited, true)) + return; + Result.clear(); + Result.push_back(NonLocalDepResult(FromBB, MemDepResult::getUnknown(), + const_cast<Value *>(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) { + + // 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; +} + +/// 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); + LLVM_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 = + 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; + } +} + +/// 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<NonLocalDepResult> &Result, + DenseMap<BasicBlock *, Value *> &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<CachedNonLocalPointerInfo::iterator, bool> 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 (auto &Entry : CacheInfo->NonLocalDeps) + if (Instruction *Inst = Entry.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 (auto &Entry : CacheInfo->NonLocalDeps) + if (Instruction *Inst = Entry.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 (auto &Entry : *Cache) { + DenseMap<BasicBlock *, Value *>::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, the result will be valid cache info, + // otherwise it isn't. + if (Cache->empty()) + CacheInfo->Pair = BBSkipFirstBlockPair(StartBB, SkipFirstBlock); + else + CacheInfo->Pair = BBSkipFirstBlockPair(); + + SmallVector<BasicBlock *, 32> Worklist; + Worklist.push_back(StartBB); + + // PredList used inside loop. + SmallVector<std::pair<BasicBlock *, PHITransAddr>, 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 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. + 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.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<BasicBlock *, 16> NewBlocks; + for (BasicBlock *Pred : PredCache.get(BB)) { + // Verify that we haven't looked at this block yet. + std::pair<DenseMap<BasicBlock *, Value *>::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<DenseMap<BasicBlock *, Value *>::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; + + 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; (void)GotWorklistLimit; + 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 true; +} + +/// If P exists in CachedNonLocalPointerInfo, remove it. +void MemoryDependenceResults::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); +} + +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) { + // 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 (auto &Entry : BlockMap) + if (Instruction *Inst = Entry.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<std::pair<Instruction *, Instruction *>, 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<TerminatorInst>(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 (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<std::pair<Instruction *, ValueIsLoadPair>, 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. + 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)); +} + +/// 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 : NonLocalDeps) { + 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; + +MemoryDependenceResults +MemoryDependenceAnalysis::run(Function &F, FunctionAnalysisManager &AM) { + auto &AA = AM.getResult<AAManager>(F); + auto &AC = AM.getResult<AssumptionAnalysis>(F); + auto &TLI = AM.getResult<TargetLibraryAnalysis>(F); + auto &DT = AM.getResult<DominatorTreeAnalysis>(F); + return MemoryDependenceResults(AA, AC, TLI, DT); +} + +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() {} + +void MemoryDependenceWrapperPass::releaseMemory() { + MemDep.reset(); +} + +void MemoryDependenceWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const { + AU.setPreservesAll(); + AU.addRequired<AssumptionCacheTracker>(); + AU.addRequired<DominatorTreeWrapperPass>(); + AU.addRequiredTransitive<AAResultsWrapperPass>(); + AU.addRequiredTransitive<TargetLibraryInfoWrapperPass>(); +} + +bool MemoryDependenceResults::invalidate(Function &F, const PreservedAnalyses &PA, + FunctionAnalysisManager::Invalidator &Inv) { + // Check whether our analysis is preserved. + auto PAC = PA.getChecker<MemoryDependenceAnalysis>(); + if (!PAC.preserved() && !PAC.preservedSet<AllAnalysesOn<Function>>()) + // If not, give up now. + return true; + + // Check whether the analyses we depend on became invalid for any reason. + if (Inv.invalidate<AAManager>(F, PA) || + Inv.invalidate<AssumptionAnalysis>(F, PA) || + Inv.invalidate<DominatorTreeAnalysis>(F, PA)) + return true; + + // Otherwise this analysis result remains valid. + return false; +} + +unsigned MemoryDependenceResults::getDefaultBlockScanLimit() const { + return BlockScanLimit; +} + +bool MemoryDependenceWrapperPass::runOnFunction(Function &F) { + auto &AA = getAnalysis<AAResultsWrapperPass>().getAAResults(); + auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); + auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(); + auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); + MemDep.emplace(AA, AC, TLI, DT); + return false; +} |