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//===- MemoryLocation.h - Memory location descriptions ----------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
/// \file
/// This file provides utility analysis objects describing memory locations.
/// These are used both by the Alias Analysis infrastructure and more
/// specialized memory analysis layers.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_ANALYSIS_MEMORYLOCATION_H
#define LLVM_ANALYSIS_MEMORYLOCATION_H
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/IR/Metadata.h"
#include "llvm/Support/TypeSize.h"
#include <optional>
namespace llvm {
class CallBase;
class Instruction;
class LoadInst;
class StoreInst;
class MemTransferInst;
class MemIntrinsic;
class AtomicCmpXchgInst;
class AtomicMemTransferInst;
class AtomicMemIntrinsic;
class AtomicRMWInst;
class AnyMemTransferInst;
class AnyMemIntrinsic;
class TargetLibraryInfo;
class VAArgInst;
class Value;
// Represents the size of a MemoryLocation. Logically, it's an
// std::optional<uint63_t> that also carries a bit to represent whether the
// integer it contains, N, is 'precise'. Precise, in this context, means that we
// know that the area of storage referenced by the given MemoryLocation must be
// precisely N bytes. An imprecise value is formed as the union of two or more
// precise values, and can conservatively represent all of the values unioned
// into it. Importantly, imprecise values are an *upper-bound* on the size of a
// MemoryLocation.
//
// Concretely, a precise MemoryLocation is (%p, 4) in
// store i32 0, i32* %p
//
// Since we know that %p must be at least 4 bytes large at this point.
// Otherwise, we have UB. An example of an imprecise MemoryLocation is (%p, 4)
// at the memcpy in
//
// %n = select i1 %foo, i64 1, i64 4
// call void @llvm.memcpy.p0i8.p0i8.i64(i8* %p, i8* %baz, i64 %n, i32 1,
// i1 false)
//
// ...Since we'll copy *up to* 4 bytes into %p, but we can't guarantee that
// we'll ever actually do so.
//
// If asked to represent a pathologically large value, this will degrade to
// std::nullopt.
// Store Scalable information in bit 62 of Value. Scalable information is
// required to do Alias Analysis on Scalable quantities
class LocationSize {
enum : uint64_t {
BeforeOrAfterPointer = ~uint64_t(0),
ScalableBit = uint64_t(1) << 62,
AfterPointer = (BeforeOrAfterPointer - 1) & ~ScalableBit,
MapEmpty = BeforeOrAfterPointer - 2,
MapTombstone = BeforeOrAfterPointer - 3,
ImpreciseBit = uint64_t(1) << 63,
// The maximum value we can represent without falling back to 'unknown'.
MaxValue = (MapTombstone - 1) & ~(ImpreciseBit | ScalableBit),
};
uint64_t Value;
// Hack to support implicit construction. This should disappear when the
// public LocationSize ctor goes away.
enum DirectConstruction { Direct };
constexpr LocationSize(uint64_t Raw, DirectConstruction) : Value(Raw) {}
constexpr LocationSize(uint64_t Raw, bool Scalable)
: Value(Raw > MaxValue ? AfterPointer
: Raw | (Scalable ? ScalableBit : uint64_t(0))) {}
static_assert(AfterPointer & ImpreciseBit,
"AfterPointer is imprecise by definition.");
static_assert(BeforeOrAfterPointer & ImpreciseBit,
"BeforeOrAfterPointer is imprecise by definition.");
static_assert(~(MaxValue & ScalableBit), "Max value don't have bit 62 set");
public:
// FIXME: Migrate all users to construct via either `precise` or `upperBound`,
// to make it more obvious at the callsite the kind of size that they're
// providing.
//
// Since the overwhelming majority of users of this provide precise values,
// this assumes the provided value is precise.
constexpr LocationSize(uint64_t Raw)
: Value(Raw > MaxValue ? AfterPointer : Raw) {}
// Create non-scalable LocationSize
static LocationSize precise(uint64_t Value) {
return LocationSize(Value, false /*Scalable*/);
}
static LocationSize precise(TypeSize Value) {
return LocationSize(Value.getKnownMinValue(), Value.isScalable());
}
static LocationSize upperBound(uint64_t Value) {
// You can't go lower than 0, so give a precise result.
if (LLVM_UNLIKELY(Value == 0))
return precise(0);
if (LLVM_UNLIKELY(Value > MaxValue))
return afterPointer();
return LocationSize(Value | ImpreciseBit, Direct);
}
static LocationSize upperBound(TypeSize Value) {
if (Value.isScalable())
return afterPointer();
return upperBound(Value.getFixedValue());
}
/// Any location after the base pointer (but still within the underlying
/// object).
constexpr static LocationSize afterPointer() {
return LocationSize(AfterPointer, Direct);
}
/// Any location before or after the base pointer (but still within the
/// underlying object).
constexpr static LocationSize beforeOrAfterPointer() {
return LocationSize(BeforeOrAfterPointer, Direct);
}
// Sentinel values, generally used for maps.
constexpr static LocationSize mapTombstone() {
return LocationSize(MapTombstone, Direct);
}
constexpr static LocationSize mapEmpty() {
return LocationSize(MapEmpty, Direct);
}
// Returns a LocationSize that can correctly represent either `*this` or
// `Other`.
LocationSize unionWith(LocationSize Other) const {
if (Other == *this)
return *this;
if (Value == BeforeOrAfterPointer || Other.Value == BeforeOrAfterPointer)
return beforeOrAfterPointer();
if (Value == AfterPointer || Other.Value == AfterPointer)
return afterPointer();
if (isScalable() || Other.isScalable())
return afterPointer();
return upperBound(std::max(getValue(), Other.getValue()));
}
bool hasValue() const {
return Value != AfterPointer && Value != BeforeOrAfterPointer;
}
bool isScalable() const { return (Value & ScalableBit); }
TypeSize getValue() const {
assert(hasValue() && "Getting value from an unknown LocationSize!");
assert((Value & ~(ImpreciseBit | ScalableBit)) < MaxValue &&
"Scalable bit of value should be masked");
return {Value & ~(ImpreciseBit | ScalableBit), isScalable()};
}
// Returns whether or not this value is precise. Note that if a value is
// precise, it's guaranteed to not be unknown.
bool isPrecise() const { return (Value & ImpreciseBit) == 0; }
// Convenience method to check if this LocationSize's value is 0.
bool isZero() const {
return hasValue() && getValue().getKnownMinValue() == 0;
}
/// Whether accesses before the base pointer are possible.
bool mayBeBeforePointer() const { return Value == BeforeOrAfterPointer; }
bool operator==(const LocationSize &Other) const {
return Value == Other.Value;
}
bool operator==(const TypeSize &Other) const {
return hasValue() && getValue() == Other;
}
bool operator!=(const LocationSize &Other) const { return !(*this == Other); }
bool operator!=(const TypeSize &Other) const { return !(*this == Other); }
// Ordering operators are not provided, since it's unclear if there's only one
// reasonable way to compare:
// - values that don't exist against values that do, and
// - precise values to imprecise values
void print(raw_ostream &OS) const;
// Returns an opaque value that represents this LocationSize. Cannot be
// reliably converted back into a LocationSize.
uint64_t toRaw() const { return Value; }
};
inline raw_ostream &operator<<(raw_ostream &OS, LocationSize Size) {
Size.print(OS);
return OS;
}
/// Representation for a specific memory location.
///
/// This abstraction can be used to represent a specific location in memory.
/// The goal of the location is to represent enough information to describe
/// abstract aliasing, modification, and reference behaviors of whatever
/// value(s) are stored in memory at the particular location.
///
/// The primary user of this interface is LLVM's Alias Analysis, but other
/// memory analyses such as MemoryDependence can use it as well.
class MemoryLocation {
public:
/// UnknownSize - This is a special value which can be used with the
/// size arguments in alias queries to indicate that the caller does not
/// know the sizes of the potential memory references.
enum : uint64_t { UnknownSize = ~UINT64_C(0) };
/// The address of the start of the location.
const Value *Ptr;
/// The maximum size of the location, in address-units, or
/// UnknownSize if the size is not known.
///
/// Note that an unknown size does not mean the pointer aliases the entire
/// virtual address space, because there are restrictions on stepping out of
/// one object and into another. See
/// http://llvm.org/docs/LangRef.html#pointeraliasing
LocationSize Size;
/// The metadata nodes which describes the aliasing of the location (each
/// member is null if that kind of information is unavailable).
AAMDNodes AATags;
void print(raw_ostream &OS) const { OS << *Ptr << " " << Size << "\n"; }
/// Return a location with information about the memory reference by the given
/// instruction.
static MemoryLocation get(const LoadInst *LI);
static MemoryLocation get(const StoreInst *SI);
static MemoryLocation get(const VAArgInst *VI);
static MemoryLocation get(const AtomicCmpXchgInst *CXI);
static MemoryLocation get(const AtomicRMWInst *RMWI);
static MemoryLocation get(const Instruction *Inst) {
return *MemoryLocation::getOrNone(Inst);
}
static std::optional<MemoryLocation> getOrNone(const Instruction *Inst);
/// Return a location representing the source of a memory transfer.
static MemoryLocation getForSource(const MemTransferInst *MTI);
static MemoryLocation getForSource(const AtomicMemTransferInst *MTI);
static MemoryLocation getForSource(const AnyMemTransferInst *MTI);
/// Return a location representing the destination of a memory set or
/// transfer.
static MemoryLocation getForDest(const MemIntrinsic *MI);
static MemoryLocation getForDest(const AtomicMemIntrinsic *MI);
static MemoryLocation getForDest(const AnyMemIntrinsic *MI);
static std::optional<MemoryLocation> getForDest(const CallBase *CI,
const TargetLibraryInfo &TLI);
/// Return a location representing a particular argument of a call.
static MemoryLocation getForArgument(const CallBase *Call, unsigned ArgIdx,
const TargetLibraryInfo *TLI);
static MemoryLocation getForArgument(const CallBase *Call, unsigned ArgIdx,
const TargetLibraryInfo &TLI) {
return getForArgument(Call, ArgIdx, &TLI);
}
/// Return a location that may access any location after Ptr, while remaining
/// within the underlying object.
static MemoryLocation getAfter(const Value *Ptr,
const AAMDNodes &AATags = AAMDNodes()) {
return MemoryLocation(Ptr, LocationSize::afterPointer(), AATags);
}
/// Return a location that may access any location before or after Ptr, while
/// remaining within the underlying object.
static MemoryLocation
getBeforeOrAfter(const Value *Ptr, const AAMDNodes &AATags = AAMDNodes()) {
return MemoryLocation(Ptr, LocationSize::beforeOrAfterPointer(), AATags);
}
MemoryLocation() : Ptr(nullptr), Size(LocationSize::beforeOrAfterPointer()) {}
explicit MemoryLocation(const Value *Ptr, LocationSize Size,
const AAMDNodes &AATags = AAMDNodes())
: Ptr(Ptr), Size(Size), AATags(AATags) {}
MemoryLocation getWithNewPtr(const Value *NewPtr) const {
MemoryLocation Copy(*this);
Copy.Ptr = NewPtr;
return Copy;
}
MemoryLocation getWithNewSize(LocationSize NewSize) const {
MemoryLocation Copy(*this);
Copy.Size = NewSize;
return Copy;
}
MemoryLocation getWithoutAATags() const {
MemoryLocation Copy(*this);
Copy.AATags = AAMDNodes();
return Copy;
}
bool operator==(const MemoryLocation &Other) const {
return Ptr == Other.Ptr && Size == Other.Size && AATags == Other.AATags;
}
};
// Specialize DenseMapInfo.
template <> struct DenseMapInfo<LocationSize> {
static inline LocationSize getEmptyKey() { return LocationSize::mapEmpty(); }
static inline LocationSize getTombstoneKey() {
return LocationSize::mapTombstone();
}
static unsigned getHashValue(const LocationSize &Val) {
return DenseMapInfo<uint64_t>::getHashValue(Val.toRaw());
}
static bool isEqual(const LocationSize &LHS, const LocationSize &RHS) {
return LHS == RHS;
}
};
template <> struct DenseMapInfo<MemoryLocation> {
static inline MemoryLocation getEmptyKey() {
return MemoryLocation(DenseMapInfo<const Value *>::getEmptyKey(),
DenseMapInfo<LocationSize>::getEmptyKey());
}
static inline MemoryLocation getTombstoneKey() {
return MemoryLocation(DenseMapInfo<const Value *>::getTombstoneKey(),
DenseMapInfo<LocationSize>::getTombstoneKey());
}
static unsigned getHashValue(const MemoryLocation &Val) {
return DenseMapInfo<const Value *>::getHashValue(Val.Ptr) ^
DenseMapInfo<LocationSize>::getHashValue(Val.Size) ^
DenseMapInfo<AAMDNodes>::getHashValue(Val.AATags);
}
static bool isEqual(const MemoryLocation &LHS, const MemoryLocation &RHS) {
return LHS == RHS;
}
};
} // namespace llvm
#endif
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