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//===- llvm/Analysis/AliasAnalysis.h - Alias Analysis Interface -*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the generic AliasAnalysis interface, which is used as the
// common interface used by all clients of alias analysis information, and
// implemented by all alias analysis implementations. Mod/Ref information is
// also captured by this interface.
//
// Implementations of this interface must implement the various virtual methods,
// which automatically provides functionality for the entire suite of client
// APIs.
//
// This API identifies memory regions with the Location class. The pointer
// component specifies the base memory address of the region. The Size specifies
// the maximum size (in address units) of the memory region, or UnknownSize if
// the size is not known. The TBAA tag identifies the "type" of the memory
// reference; see the TypeBasedAliasAnalysis class for details.
//
// Some non-obvious details include:
// - Pointers that point to two completely different objects in memory never
// alias, regardless of the value of the Size component.
// - NoAlias doesn't imply inequal pointers. The most obvious example of this
// is two pointers to constant memory. Even if they are equal, constant
// memory is never stored to, so there will never be any dependencies.
// In this and other situations, the pointers may be both NoAlias and
// MustAlias at the same time. The current API can only return one result,
// though this is rarely a problem in practice.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ANALYSIS_ALIAS_ANALYSIS_H
#define LLVM_ANALYSIS_ALIAS_ANALYSIS_H
#include "llvm/Support/CallSite.h"
#include "llvm/ADT/DenseMap.h"
namespace llvm {
class LoadInst;
class StoreInst;
class VAArgInst;
class TargetData;
class Pass;
class AnalysisUsage;
class MemTransferInst;
class MemIntrinsic;
class AliasAnalysis {
protected:
const TargetData *TD;
private:
AliasAnalysis *AA; // Previous Alias Analysis to chain to.
protected:
/// InitializeAliasAnalysis - Subclasses must call this method to initialize
/// the AliasAnalysis interface before any other methods are called. This is
/// typically called by the run* methods of these subclasses. This may be
/// called multiple times.
///
void InitializeAliasAnalysis(Pass *P);
/// getAnalysisUsage - All alias analysis implementations should invoke this
/// directly (using AliasAnalysis::getAnalysisUsage(AU)).
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
public:
static char ID; // Class identification, replacement for typeinfo
AliasAnalysis() : TD(0), AA(0) {}
virtual ~AliasAnalysis(); // We want to be subclassed
/// 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.
static uint64_t const UnknownSize = ~UINT64_C(0);
/// getTargetData - Return a pointer to the current TargetData object, or
/// null if no TargetData object is available.
///
const TargetData *getTargetData() const { return TD; }
/// getTypeStoreSize - Return the TargetData store size for the given type,
/// if known, or a conservative value otherwise.
///
uint64_t getTypeStoreSize(Type *Ty);
//===--------------------------------------------------------------------===//
/// Alias Queries...
///
/// Location - A description of a memory location.
struct Location {
/// Ptr - The address of the start of the location.
const Value *Ptr;
/// Size - 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
uint64_t Size;
/// TBAATag - The metadata node which describes the TBAA type of
/// the location, or null if there is no known unique tag.
const MDNode *TBAATag;
explicit Location(const Value *P = 0, uint64_t S = UnknownSize,
const MDNode *N = 0)
: Ptr(P), Size(S), TBAATag(N) {}
Location getWithNewPtr(const Value *NewPtr) const {
Location Copy(*this);
Copy.Ptr = NewPtr;
return Copy;
}
Location getWithNewSize(uint64_t NewSize) const {
Location Copy(*this);
Copy.Size = NewSize;
return Copy;
}
Location getWithoutTBAATag() const {
Location Copy(*this);
Copy.TBAATag = 0;
return Copy;
}
};
/// getLocation - Fill in Loc with information about the memory reference by
/// the given instruction.
Location getLocation(const LoadInst *LI);
Location getLocation(const StoreInst *SI);
Location getLocation(const VAArgInst *VI);
Location getLocation(const AtomicCmpXchgInst *CXI);
Location getLocation(const AtomicRMWInst *RMWI);
static Location getLocationForSource(const MemTransferInst *MTI);
static Location getLocationForDest(const MemIntrinsic *MI);
/// Alias analysis result - Either we know for sure that it does not alias, we
/// know for sure it must alias, or we don't know anything: The two pointers
/// _might_ alias. This enum is designed so you can do things like:
/// if (AA.alias(P1, P2)) { ... }
/// to check to see if two pointers might alias.
///
/// See docs/AliasAnalysis.html for more information on the specific meanings
/// of these values.
///
enum AliasResult {
NoAlias = 0, ///< No dependencies.
MayAlias, ///< Anything goes.
PartialAlias, ///< Pointers differ, but pointees overlap.
MustAlias ///< Pointers are equal.
};
/// alias - The main low level interface to the alias analysis implementation.
/// Returns an AliasResult indicating whether the two pointers are aliased to
/// each other. This is the interface that must be implemented by specific
/// alias analysis implementations.
virtual AliasResult alias(const Location &LocA, const Location &LocB);
/// alias - A convenience wrapper.
AliasResult alias(const Value *V1, uint64_t V1Size,
const Value *V2, uint64_t V2Size) {
return alias(Location(V1, V1Size), Location(V2, V2Size));
}
/// alias - A convenience wrapper.
AliasResult alias(const Value *V1, const Value *V2) {
return alias(V1, UnknownSize, V2, UnknownSize);
}
/// isNoAlias - A trivial helper function to check to see if the specified
/// pointers are no-alias.
bool isNoAlias(const Location &LocA, const Location &LocB) {
return alias(LocA, LocB) == NoAlias;
}
/// isNoAlias - A convenience wrapper.
bool isNoAlias(const Value *V1, uint64_t V1Size,
const Value *V2, uint64_t V2Size) {
return isNoAlias(Location(V1, V1Size), Location(V2, V2Size));
}
/// isMustAlias - A convenience wrapper.
bool isMustAlias(const Location &LocA, const Location &LocB) {
return alias(LocA, LocB) == MustAlias;
}
/// isMustAlias - A convenience wrapper.
bool isMustAlias(const Value *V1, const Value *V2) {
return alias(V1, 1, V2, 1) == MustAlias;
}
/// pointsToConstantMemory - If the specified memory location is
/// known to be constant, return true. If OrLocal is true and the
/// specified memory location is known to be "local" (derived from
/// an alloca), return true. Otherwise return false.
virtual bool pointsToConstantMemory(const Location &Loc,
bool OrLocal = false);
/// pointsToConstantMemory - A convenient wrapper.
bool pointsToConstantMemory(const Value *P, bool OrLocal = false) {
return pointsToConstantMemory(Location(P), OrLocal);
}
//===--------------------------------------------------------------------===//
/// Simple mod/ref information...
///
/// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are
/// bits which may be or'd together.
///
enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
/// These values define additional bits used to define the
/// ModRefBehavior values.
enum { Nowhere = 0, ArgumentPointees = 4, Anywhere = 8 | ArgumentPointees };
/// ModRefBehavior - Summary of how a function affects memory in the program.
/// Loads from constant globals are not considered memory accesses for this
/// interface. Also, functions may freely modify stack space local to their
/// invocation without having to report it through these interfaces.
enum ModRefBehavior {
/// DoesNotAccessMemory - This function does not perform any non-local loads
/// or stores to memory.
///
/// This property corresponds to the GCC 'const' attribute.
/// This property corresponds to the LLVM IR 'readnone' attribute.
/// This property corresponds to the IntrNoMem LLVM intrinsic flag.
DoesNotAccessMemory = Nowhere | NoModRef,
/// OnlyReadsArgumentPointees - The only memory references in this function
/// (if it has any) are non-volatile loads from objects pointed to by its
/// pointer-typed arguments, with arbitrary offsets.
///
/// This property corresponds to the IntrReadArgMem LLVM intrinsic flag.
OnlyReadsArgumentPointees = ArgumentPointees | Ref,
/// OnlyAccessesArgumentPointees - The only memory references in this
/// function (if it has any) are non-volatile loads and stores from objects
/// pointed to by its pointer-typed arguments, with arbitrary offsets.
///
/// This property corresponds to the IntrReadWriteArgMem LLVM intrinsic flag.
OnlyAccessesArgumentPointees = ArgumentPointees | ModRef,
/// OnlyReadsMemory - This function does not perform any non-local stores or
/// volatile loads, but may read from any memory location.
///
/// This property corresponds to the GCC 'pure' attribute.
/// This property corresponds to the LLVM IR 'readonly' attribute.
/// This property corresponds to the IntrReadMem LLVM intrinsic flag.
OnlyReadsMemory = Anywhere | Ref,
/// UnknownModRefBehavior - This indicates that the function could not be
/// classified into one of the behaviors above.
UnknownModRefBehavior = Anywhere | ModRef
};
/// getModRefBehavior - Return the behavior when calling the given call site.
virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
/// getModRefBehavior - Return the behavior when calling the given function.
/// For use when the call site is not known.
virtual ModRefBehavior getModRefBehavior(const Function *F);
/// doesNotAccessMemory - If the specified call is known to never read or
/// write memory, return true. If the call only reads from known-constant
/// memory, it is also legal to return true. Calls that unwind the stack
/// are legal for this predicate.
///
/// Many optimizations (such as CSE and LICM) can be performed on such calls
/// without worrying about aliasing properties, and many calls have this
/// property (e.g. calls to 'sin' and 'cos').
///
/// This property corresponds to the GCC 'const' attribute.
///
bool doesNotAccessMemory(ImmutableCallSite CS) {
return getModRefBehavior(CS) == DoesNotAccessMemory;
}
/// doesNotAccessMemory - If the specified function is known to never read or
/// write memory, return true. For use when the call site is not known.
///
bool doesNotAccessMemory(const Function *F) {
return getModRefBehavior(F) == DoesNotAccessMemory;
}
/// onlyReadsMemory - If the specified call is known to only read from
/// non-volatile memory (or not access memory at all), return true. Calls
/// that unwind the stack are legal for this predicate.
///
/// This property allows many common optimizations to be performed in the
/// absence of interfering store instructions, such as CSE of strlen calls.
///
/// This property corresponds to the GCC 'pure' attribute.
///
bool onlyReadsMemory(ImmutableCallSite CS) {
return onlyReadsMemory(getModRefBehavior(CS));
}
/// onlyReadsMemory - If the specified function is known to only read from
/// non-volatile memory (or not access memory at all), return true. For use
/// when the call site is not known.
///
bool onlyReadsMemory(const Function *F) {
return onlyReadsMemory(getModRefBehavior(F));
}
/// onlyReadsMemory - Return true if functions with the specified behavior are
/// known to only read from non-volatile memory (or not access memory at all).
///
static bool onlyReadsMemory(ModRefBehavior MRB) {
return !(MRB & Mod);
}
/// onlyAccessesArgPointees - Return true if functions with the specified
/// behavior are known to read and write at most from objects pointed to by
/// their pointer-typed arguments (with arbitrary offsets).
///
static bool onlyAccessesArgPointees(ModRefBehavior MRB) {
return !(MRB & Anywhere & ~ArgumentPointees);
}
/// doesAccessArgPointees - Return true if functions with the specified
/// behavior are known to potentially read or write from objects pointed
/// to be their pointer-typed arguments (with arbitrary offsets).
///
static bool doesAccessArgPointees(ModRefBehavior MRB) {
return (MRB & ModRef) && (MRB & ArgumentPointees);
}
/// getModRefInfo - Return information about whether or not an instruction may
/// read or write the specified memory location. An instruction
/// that doesn't read or write memory may be trivially LICM'd for example.
ModRefResult getModRefInfo(const Instruction *I,
const Location &Loc) {
switch (I->getOpcode()) {
case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, Loc);
case Instruction::Load: return getModRefInfo((const LoadInst*)I, Loc);
case Instruction::Store: return getModRefInfo((const StoreInst*)I, Loc);
case Instruction::Fence: return getModRefInfo((const FenceInst*)I, Loc);
case Instruction::AtomicCmpXchg:
return getModRefInfo((const AtomicCmpXchgInst*)I, Loc);
case Instruction::AtomicRMW:
return getModRefInfo((const AtomicRMWInst*)I, Loc);
case Instruction::Call: return getModRefInfo((const CallInst*)I, Loc);
case Instruction::Invoke: return getModRefInfo((const InvokeInst*)I,Loc);
default: return NoModRef;
}
}
/// getModRefInfo - A convenience wrapper.
ModRefResult getModRefInfo(const Instruction *I,
const Value *P, uint64_t Size) {
return getModRefInfo(I, Location(P, Size));
}
/// getModRefInfo (for call sites) - Return whether information about whether
/// a particular call site modifies or reads the specified memory location.
virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
const Location &Loc);
/// getModRefInfo (for call sites) - A convenience wrapper.
ModRefResult getModRefInfo(ImmutableCallSite CS,
const Value *P, uint64_t Size) {
return getModRefInfo(CS, Location(P, Size));
}
/// getModRefInfo (for calls) - Return whether information about whether
/// a particular call modifies or reads the specified memory location.
ModRefResult getModRefInfo(const CallInst *C, const Location &Loc) {
return getModRefInfo(ImmutableCallSite(C), Loc);
}
/// getModRefInfo (for calls) - A convenience wrapper.
ModRefResult getModRefInfo(const CallInst *C, const Value *P, uint64_t Size) {
return getModRefInfo(C, Location(P, Size));
}
/// getModRefInfo (for invokes) - Return whether information about whether
/// a particular invoke modifies or reads the specified memory location.
ModRefResult getModRefInfo(const InvokeInst *I,
const Location &Loc) {
return getModRefInfo(ImmutableCallSite(I), Loc);
}
/// getModRefInfo (for invokes) - A convenience wrapper.
ModRefResult getModRefInfo(const InvokeInst *I,
const Value *P, uint64_t Size) {
return getModRefInfo(I, Location(P, Size));
}
/// getModRefInfo (for loads) - Return whether information about whether
/// a particular load modifies or reads the specified memory location.
ModRefResult getModRefInfo(const LoadInst *L, const Location &Loc);
/// getModRefInfo (for loads) - A convenience wrapper.
ModRefResult getModRefInfo(const LoadInst *L, const Value *P, uint64_t Size) {
return getModRefInfo(L, Location(P, Size));
}
/// getModRefInfo (for stores) - Return whether information about whether
/// a particular store modifies or reads the specified memory location.
ModRefResult getModRefInfo(const StoreInst *S, const Location &Loc);
/// getModRefInfo (for stores) - A convenience wrapper.
ModRefResult getModRefInfo(const StoreInst *S, const Value *P, uint64_t Size){
return getModRefInfo(S, Location(P, Size));
}
/// getModRefInfo (for fences) - Return whether information about whether
/// a particular store modifies or reads the specified memory location.
ModRefResult getModRefInfo(const FenceInst *S, const Location &Loc) {
// Conservatively correct. (We could possibly be a bit smarter if
// Loc is a alloca that doesn't escape.)
return ModRef;
}
/// getModRefInfo (for fences) - A convenience wrapper.
ModRefResult getModRefInfo(const FenceInst *S, const Value *P, uint64_t Size){
return getModRefInfo(S, Location(P, Size));
}
/// getModRefInfo (for cmpxchges) - Return whether information about whether
/// a particular cmpxchg modifies or reads the specified memory location.
ModRefResult getModRefInfo(const AtomicCmpXchgInst *CX, const Location &Loc);
/// getModRefInfo (for cmpxchges) - A convenience wrapper.
ModRefResult getModRefInfo(const AtomicCmpXchgInst *CX,
const Value *P, unsigned Size) {
return getModRefInfo(CX, Location(P, Size));
}
/// getModRefInfo (for atomicrmws) - Return whether information about whether
/// a particular atomicrmw modifies or reads the specified memory location.
ModRefResult getModRefInfo(const AtomicRMWInst *RMW, const Location &Loc);
/// getModRefInfo (for atomicrmws) - A convenience wrapper.
ModRefResult getModRefInfo(const AtomicRMWInst *RMW,
const Value *P, unsigned Size) {
return getModRefInfo(RMW, Location(P, Size));
}
/// getModRefInfo (for va_args) - Return whether information about whether
/// a particular va_arg modifies or reads the specified memory location.
ModRefResult getModRefInfo(const VAArgInst* I, const Location &Loc);
/// getModRefInfo (for va_args) - A convenience wrapper.
ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, uint64_t Size){
return getModRefInfo(I, Location(P, Size));
}
/// getModRefInfo - Return information about whether two call sites may refer
/// to the same set of memory locations. See
/// http://llvm.org/docs/AliasAnalysis.html#ModRefInfo
/// for details.
virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
ImmutableCallSite CS2);
//===--------------------------------------------------------------------===//
/// Higher level methods for querying mod/ref information.
///
/// canBasicBlockModify - Return true if it is possible for execution of the
/// specified basic block to modify the value pointed to by Ptr.
bool canBasicBlockModify(const BasicBlock &BB, const Location &Loc);
/// canBasicBlockModify - A convenience wrapper.
bool canBasicBlockModify(const BasicBlock &BB, const Value *P, uint64_t Size){
return canBasicBlockModify(BB, Location(P, Size));
}
/// canInstructionRangeModify - Return true if it is possible for the
/// execution of the specified instructions to modify the value pointed to by
/// Ptr. The instructions to consider are all of the instructions in the
/// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block.
bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
const Location &Loc);
/// canInstructionRangeModify - A convenience wrapper.
bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
const Value *Ptr, uint64_t Size) {
return canInstructionRangeModify(I1, I2, Location(Ptr, Size));
}
//===--------------------------------------------------------------------===//
/// Methods that clients should call when they transform the program to allow
/// alias analyses to update their internal data structures. Note that these
/// methods may be called on any instruction, regardless of whether or not
/// they have pointer-analysis implications.
///
/// deleteValue - This method should be called whenever an LLVM Value is
/// deleted from the program, for example when an instruction is found to be
/// redundant and is eliminated.
///
virtual void deleteValue(Value *V);
/// copyValue - This method should be used whenever a preexisting value in the
/// program is copied or cloned, introducing a new value. Note that analysis
/// implementations should tolerate clients that use this method to introduce
/// the same value multiple times: if the analysis already knows about a
/// value, it should ignore the request.
///
virtual void copyValue(Value *From, Value *To);
/// addEscapingUse - This method should be used whenever an escaping use is
/// added to a pointer value. Analysis implementations may either return
/// conservative responses for that value in the future, or may recompute
/// some or all internal state to continue providing precise responses.
///
/// Escaping uses are considered by anything _except_ the following:
/// - GEPs or bitcasts of the pointer
/// - Loads through the pointer
/// - Stores through (but not of) the pointer
virtual void addEscapingUse(Use &U);
/// replaceWithNewValue - This method is the obvious combination of the two
/// above, and it provided as a helper to simplify client code.
///
void replaceWithNewValue(Value *Old, Value *New) {
copyValue(Old, New);
deleteValue(Old);
}
};
// Specialize DenseMapInfo for Location.
template<>
struct DenseMapInfo<AliasAnalysis::Location> {
static inline AliasAnalysis::Location getEmptyKey() {
return
AliasAnalysis::Location(DenseMapInfo<const Value *>::getEmptyKey(),
0, 0);
}
static inline AliasAnalysis::Location getTombstoneKey() {
return
AliasAnalysis::Location(DenseMapInfo<const Value *>::getTombstoneKey(),
0, 0);
}
static unsigned getHashValue(const AliasAnalysis::Location &Val) {
return DenseMapInfo<const Value *>::getHashValue(Val.Ptr) ^
DenseMapInfo<uint64_t>::getHashValue(Val.Size) ^
DenseMapInfo<const MDNode *>::getHashValue(Val.TBAATag);
}
static bool isEqual(const AliasAnalysis::Location &LHS,
const AliasAnalysis::Location &RHS) {
return LHS.Ptr == RHS.Ptr &&
LHS.Size == RHS.Size &&
LHS.TBAATag == RHS.TBAATag;
}
};
/// isNoAliasCall - Return true if this pointer is returned by a noalias
/// function.
bool isNoAliasCall(const Value *V);
/// isIdentifiedObject - Return true if this pointer refers to a distinct and
/// identifiable object. This returns true for:
/// Global Variables and Functions (but not Global Aliases)
/// Allocas and Mallocs
/// ByVal and NoAlias Arguments
/// NoAlias returns
///
bool isIdentifiedObject(const Value *V);
/// isKnownNonNull - Return true if this pointer couldn't possibly be null by
/// its definition. This returns true for allocas, non-extern-weak globals and
/// byval arguments.
bool isKnownNonNull(const Value *V);
} // End llvm namespace
#endif