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//===- llvm/Analysis/MemoryDependenceAnalysis.h - Memory Deps ---*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file defines the MemoryDependenceAnalysis analysis pass.
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/PointerEmbeddedInt.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/PointerSumType.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/PredIteratorCache.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Pass.h"
#include "llvm/Support/ErrorHandling.h"
#include <cassert>
#include <cstdint>
#include <utility>
#include <vector>
namespace llvm {
class AssumptionCache;
class DominatorTree;
class Function;
class Instruction;
class LoadInst;
class PHITransAddr;
class TargetLibraryInfo;
class PhiValues;
class Value;
/// A memory dependence query can return one of three different answers.
class MemDepResult {
enum DepType {
/// Clients of MemDep never see this.
/// Entries with this marker occur in a LocalDeps map or NonLocalDeps map
/// when the instruction they previously referenced was removed from
/// MemDep. In either case, the entry may include an instruction pointer.
/// If so, the pointer is an instruction in the block where scanning can
/// start from, saving some work.
/// In a default-constructed MemDepResult object, the type will be Invalid
/// and the instruction pointer will be null.
Invalid = 0,
/// This is a dependence on the specified instruction which clobbers the
/// desired value. The pointer member of the MemDepResult pair holds the
/// instruction that clobbers the memory. For example, this occurs when we
/// see a may-aliased store to the memory location we care about.
/// There are several cases that may be interesting here:
/// 1. Loads are clobbered by may-alias stores.
/// 2. Loads are considered clobbered by partially-aliased loads. The
/// client may choose to analyze deeper into these cases.
/// This is a dependence on the specified instruction which defines or
/// produces the desired memory location. The pointer member of the
/// MemDepResult pair holds the instruction that defines the memory.
/// Cases of interest:
/// 1. This could be a load or store for dependence queries on
/// load/store. The value loaded or stored is the produced value.
/// Note that the pointer operand may be different than that of the
/// queried pointer due to must aliases and phi translation. Note
/// that the def may not be the same type as the query, the pointers
/// may just be must aliases.
/// 2. For loads and stores, this could be an allocation instruction. In
/// this case, the load is loading an undef value or a store is the
/// first store to (that part of) the allocation.
/// 3. Dependence queries on calls return Def only when they are readonly
/// calls or memory use intrinsics with identical callees and no
/// intervening clobbers. No validation is done that the operands to
/// the calls are the same.
/// This marker indicates that the query has no known dependency in the
/// specified block.
/// More detailed state info is encoded in the upper part of the pair (i.e.
/// the Instruction*)
/// If DepType is "Other", the upper part of the sum type is an encoding of
/// the following more detailed type information.
enum OtherType {
/// This marker indicates that the query has no dependency in the specified
/// block.
/// To find out more, the client should query other predecessor blocks.
NonLocal = 1,
/// This marker indicates that the query has no dependency in the specified
/// function.
/// This marker indicates that the query dependency is unknown.
using ValueTy = PointerSumType<
DepType, PointerSumTypeMember<Invalid, Instruction *>,
PointerSumTypeMember<Clobber, Instruction *>,
PointerSumTypeMember<Def, Instruction *>,
PointerSumTypeMember<Other, PointerEmbeddedInt<OtherType, 3>>>;
ValueTy Value;
explicit MemDepResult(ValueTy V) : Value(V) {}
MemDepResult() = default;
/// get methods: These are static ctor methods for creating various
/// MemDepResult kinds.
static MemDepResult getDef(Instruction *Inst) {
assert(Inst && "Def requires inst");
return MemDepResult(ValueTy::create<Def>(Inst));
static MemDepResult getClobber(Instruction *Inst) {
assert(Inst && "Clobber requires inst");
return MemDepResult(ValueTy::create<Clobber>(Inst));
static MemDepResult getNonLocal() {
return MemDepResult(ValueTy::create<Other>(NonLocal));
static MemDepResult getNonFuncLocal() {
return MemDepResult(ValueTy::create<Other>(NonFuncLocal));
static MemDepResult getUnknown() {
return MemDepResult(ValueTy::create<Other>(Unknown));
/// Tests if this MemDepResult represents a query that is an instruction
/// clobber dependency.
bool isClobber() const { return<Clobber>(); }
/// Tests if this MemDepResult represents a query that is an instruction
/// definition dependency.
bool isDef() const { return<Def>(); }
/// Tests if this MemDepResult represents a query that is transparent to the
/// start of the block, but where a non-local hasn't been done.
bool isNonLocal() const {
return<Other>() && Value.cast<Other>() == NonLocal;
/// Tests if this MemDepResult represents a query that is transparent to the
/// start of the function.
bool isNonFuncLocal() const {
return<Other>() && Value.cast<Other>() == NonFuncLocal;
/// Tests if this MemDepResult represents a query which cannot and/or will
/// not be computed.
bool isUnknown() const {
return<Other>() && Value.cast<Other>() == Unknown;
/// If this is a normal dependency, returns the instruction that is depended
/// on. Otherwise, returns null.
Instruction *getInst() const {
switch (Value.getTag()) {
case Invalid:
return Value.cast<Invalid>();
case Clobber:
return Value.cast<Clobber>();
case Def:
return Value.cast<Def>();
case Other:
return nullptr;
llvm_unreachable("Unknown discriminant!");
bool operator==(const MemDepResult &M) const { return Value == M.Value; }
bool operator!=(const MemDepResult &M) const { return Value != M.Value; }
bool operator<(const MemDepResult &M) const { return Value < M.Value; }
bool operator>(const MemDepResult &M) const { return Value > M.Value; }
friend class MemoryDependenceResults;
/// Tests if this is a MemDepResult in its dirty/invalid. state.
bool isDirty() const { return<Invalid>(); }
static MemDepResult getDirty(Instruction *Inst) {
return MemDepResult(ValueTy::create<Invalid>(Inst));
/// This is an entry in the NonLocalDepInfo cache.
/// For each BasicBlock (the BB entry) it keeps a MemDepResult.
class NonLocalDepEntry {
BasicBlock *BB;
MemDepResult Result;
NonLocalDepEntry(BasicBlock *bb, MemDepResult result)
: BB(bb), Result(result) {}
// This is used for searches.
NonLocalDepEntry(BasicBlock *bb) : BB(bb) {}
// BB is the sort key, it can't be changed.
BasicBlock *getBB() const { return BB; }
void setResult(const MemDepResult &R) { Result = R; }
const MemDepResult &getResult() const { return Result; }
bool operator<(const NonLocalDepEntry &RHS) const { return BB < RHS.BB; }
/// This is a result from a NonLocal dependence query.
/// For each BasicBlock (the BB entry) it keeps a MemDepResult and the
/// (potentially phi translated) address that was live in the block.
class NonLocalDepResult {
NonLocalDepEntry Entry;
Value *Address;
NonLocalDepResult(BasicBlock *bb, MemDepResult result, Value *address)
: Entry(bb, result), Address(address) {}
// BB is the sort key, it can't be changed.
BasicBlock *getBB() const { return Entry.getBB(); }
void setResult(const MemDepResult &R, Value *Addr) {
Address = Addr;
const MemDepResult &getResult() const { return Entry.getResult(); }
/// Returns the address of this pointer in this block.
/// This can be different than the address queried for the non-local result
/// because of phi translation. This returns null if the address was not
/// available in a block (i.e. because phi translation failed) or if this is
/// a cached result and that address was deleted.
/// The address is always null for a non-local 'call' dependence.
Value *getAddress() const { return Address; }
/// Provides a lazy, caching interface for making common memory aliasing
/// information queries, backed by LLVM's alias analysis passes.
/// The dependency information returned is somewhat unusual, but is pragmatic.
/// If queried about a store or call that might modify memory, the analysis
/// will return the instruction[s] that may either load from that memory or
/// store to it. If queried with a load or call that can never modify memory,
/// the analysis will return calls and stores that might modify the pointer,
/// but generally does not return loads unless a) they are volatile, or
/// b) they load from *must-aliased* pointers. Returning a dependence on
/// must-alias'd pointers instead of all pointers interacts well with the
/// internal caching mechanism.
class MemoryDependenceResults {
// A map from instructions to their dependency.
using LocalDepMapType = DenseMap<Instruction *, MemDepResult>;
LocalDepMapType LocalDeps;
using NonLocalDepInfo = std::vector<NonLocalDepEntry>;
/// A pair<Value*, bool> where the bool is true if the dependence is a read
/// only dependence, false if read/write.
using ValueIsLoadPair = PointerIntPair<const Value *, 1, bool>;
/// This pair is used when caching information for a block.
/// If the pointer is null, the cache value is not a full query that starts
/// at the specified block. If non-null, the bool indicates whether or not
/// the contents of the block was skipped.
using BBSkipFirstBlockPair = PointerIntPair<BasicBlock *, 1, bool>;
/// This record is the information kept for each (value, is load) pair.
struct NonLocalPointerInfo {
/// The pair of the block and the skip-first-block flag.
BBSkipFirstBlockPair Pair;
/// The results of the query for each relevant block.
NonLocalDepInfo NonLocalDeps;
/// The maximum size of the dereferences of the pointer.
/// May be UnknownSize if the sizes are unknown.
LocationSize Size = LocationSize::unknown();
/// The AA tags associated with dereferences of the pointer.
/// The members may be null if there are no tags or conflicting tags.
AAMDNodes AATags;
NonLocalPointerInfo() = default;
/// Cache storing single nonlocal def for the instruction.
/// It is set when nonlocal def would be found in function returning only
/// local dependencies.
DenseMap<AssertingVH<const Value>, NonLocalDepResult> NonLocalDefsCache;
using ReverseNonLocalDefsCacheTy =
DenseMap<Instruction *, SmallPtrSet<const Value*, 4>>;
ReverseNonLocalDefsCacheTy ReverseNonLocalDefsCache;
/// This map stores the cached results of doing a pointer lookup at the
/// bottom of a block.
/// The key of this map is the pointer+isload bit, the value is a list of
/// <bb->result> mappings.
using CachedNonLocalPointerInfo =
DenseMap<ValueIsLoadPair, NonLocalPointerInfo>;
CachedNonLocalPointerInfo NonLocalPointerDeps;
// A map from instructions to their non-local pointer dependencies.
using ReverseNonLocalPtrDepTy =
DenseMap<Instruction *, SmallPtrSet<ValueIsLoadPair, 4>>;
ReverseNonLocalPtrDepTy ReverseNonLocalPtrDeps;
/// This is the instruction we keep for each cached access that we have for
/// an instruction.
/// The pointer is an owning pointer and the bool indicates whether we have
/// any dirty bits in the set.
using PerInstNLInfo = std::pair<NonLocalDepInfo, bool>;
// A map from instructions to their non-local dependencies.
using NonLocalDepMapType = DenseMap<Instruction *, PerInstNLInfo>;
NonLocalDepMapType NonLocalDeps;
// A reverse mapping from dependencies to the dependees. This is
// used when removing instructions to keep the cache coherent.
using ReverseDepMapType =
DenseMap<Instruction *, SmallPtrSet<Instruction *, 4>>;
ReverseDepMapType ReverseLocalDeps;
// A reverse mapping from dependencies to the non-local dependees.
ReverseDepMapType ReverseNonLocalDeps;
/// Current AA implementation, just a cache.
AliasAnalysis &AA;
AssumptionCache &AC;
const TargetLibraryInfo &TLI;
DominatorTree &DT;
PhiValues &PV;
PredIteratorCache PredCache;
unsigned DefaultBlockScanLimit;
MemoryDependenceResults(AliasAnalysis &AA, AssumptionCache &AC,
const TargetLibraryInfo &TLI, DominatorTree &DT,
PhiValues &PV, unsigned DefaultBlockScanLimit)
DefaultBlockScanLimit(DefaultBlockScanLimit) {}
/// Handle invalidation in the new PM.
bool invalidate(Function &F, const PreservedAnalyses &PA,
FunctionAnalysisManager::Invalidator &Inv);
/// Some methods limit the number of instructions they will examine.
/// The return value of this method is the default limit that will be
/// used if no limit is explicitly passed in.
unsigned getDefaultBlockScanLimit() const;
/// Returns the instruction on which a memory operation depends.
/// See the class comment for more details. It is illegal to call this on
/// non-memory instructions.
MemDepResult getDependency(Instruction *QueryInst,
OrderedBasicBlock *OBB = nullptr);
/// 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 NonLocalDepInfo &getNonLocalCallDependency(CallBase *QueryCall);
/// Perform a full dependency query for an access to the QueryInst's
/// specified memory location, returning the set of instructions that either
/// define or clobber the value.
/// Warning: For a volatile query instruction, the dependencies will be
/// accurate, and thus usable for reordering, but it is never legal to
/// remove the query instruction.
/// This method assumes the pointer has a "NonLocal" dependency within
/// QueryInst's parent basic block.
void getNonLocalPointerDependency(Instruction *QueryInst,
SmallVectorImpl<NonLocalDepResult> &Result);
/// Removes an instruction from the dependence analysis, updating the
/// dependence of instructions that previously depended on it.
void removeInstruction(Instruction *InstToRemove);
/// Invalidates 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 invalidateCachedPointerInfo(Value *Ptr);
/// Clears the PredIteratorCache info.
/// This needs to be done when the CFG changes, e.g., due to splitting
/// critical edges.
void invalidateCachedPredecessors();
/// Returns 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. \p Limit
/// can be used to set the maximum number of instructions that will be
/// examined to find the pointer dependency. On return, it will be set to
/// the number of instructions left to examine. If a null pointer is passed
/// in, the limit will default to the value of -memdep-block-scan-limit.
/// Note that this is an uncached query, and thus may be inefficient.
MemDepResult getPointerDependencyFrom(const MemoryLocation &Loc, bool isLoad,
BasicBlock::iterator ScanIt,
BasicBlock *BB,
Instruction *QueryInst = nullptr,
unsigned *Limit = nullptr,
OrderedBasicBlock *OBB = nullptr);
getSimplePointerDependencyFrom(const MemoryLocation &MemLoc, bool isLoad,
BasicBlock::iterator ScanIt, BasicBlock *BB,
Instruction *QueryInst, unsigned *Limit,
OrderedBasicBlock *OBB);
/// This analysis looks for other loads and stores with
/// metadata and the same pointer operand. Returns Unknown if it does not
/// find anything, and Def if it can be assumed that 2 instructions load or
/// store the same value and NonLocal which indicate that non-local Def was
/// found, which can be retrieved by calling getNonLocalPointerDependency
/// with the same queried instruction.
MemDepResult getInvariantGroupPointerDependency(LoadInst *LI, BasicBlock *BB);
/// 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.
static unsigned getLoadLoadClobberFullWidthSize(const Value *MemLocBase,
int64_t MemLocOffs,
unsigned MemLocSize,
const LoadInst *LI);
/// Release memory in caches.
void releaseMemory();
MemDepResult getCallDependencyFrom(CallBase *Call, bool isReadOnlyCall,
BasicBlock::iterator ScanIt,
BasicBlock *BB);
bool getNonLocalPointerDepFromBB(Instruction *QueryInst,
const PHITransAddr &Pointer,
const MemoryLocation &Loc, bool isLoad,
BasicBlock *BB,
SmallVectorImpl<NonLocalDepResult> &Result,
DenseMap<BasicBlock *, Value *> &Visited,
bool SkipFirstBlock = false);
MemDepResult GetNonLocalInfoForBlock(Instruction *QueryInst,
const MemoryLocation &Loc, bool isLoad,
BasicBlock *BB, NonLocalDepInfo *Cache,
unsigned NumSortedEntries);
void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P);
void verifyRemoved(Instruction *Inst) const;
/// An analysis that produces \c MemoryDependenceResults for a function.
/// This is essentially a no-op because the results are computed entirely
/// lazily.
class MemoryDependenceAnalysis
: public AnalysisInfoMixin<MemoryDependenceAnalysis> {
friend AnalysisInfoMixin<MemoryDependenceAnalysis>;
static AnalysisKey Key;
unsigned DefaultBlockScanLimit;
using Result = MemoryDependenceResults;
MemoryDependenceAnalysis(unsigned DefaultBlockScanLimit) : DefaultBlockScanLimit(DefaultBlockScanLimit) { }
MemoryDependenceResults run(Function &F, FunctionAnalysisManager &AM);
/// A wrapper analysis pass for the legacy pass manager that exposes a \c
/// MemoryDepnedenceResults instance.
class MemoryDependenceWrapperPass : public FunctionPass {
Optional<MemoryDependenceResults> MemDep;
static char ID;
~MemoryDependenceWrapperPass() override;
/// Pass Implementation stuff. This doesn't do any analysis eagerly.
bool runOnFunction(Function &) override;
/// Clean up memory in between runs
void releaseMemory() override;
/// Does not modify anything. It uses Value Numbering and Alias Analysis.
void getAnalysisUsage(AnalysisUsage &AU) const override;
MemoryDependenceResults &getMemDep() { return *MemDep; }
} // end namespace llvm