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//===- llvm/Analysis/AliasAnalysis.h - Alias Analysis Interface -*- C++ -*-===//
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// The LLVM Compiler Infrastructure
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//===----------------------------------------------------------------------===//
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// This file defines the generic AliasAnalysis interface, which is used as the
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// common interface used by all clients of alias analysis information, and
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// implemented by all alias analysis implementations. Mod/Ref information is
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// also captured by this interface.
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// Implementations of this interface must implement the various virtual methods,
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// which automatically provides functionality for the entire suite of client
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// This API represents memory as a (Pointer, Size) pair. The Pointer component
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// specifies the base memory address of the region, the Size specifies how large
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// of an area is being queried. If Size is 0, two pointers only alias if they
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// are exactly equal. If size is greater than zero, but small, the two pointers
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// alias if the areas pointed to overlap. If the size is very large (ie, ~0U),
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// then the two pointers alias if they may be pointing to components of the same
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// memory object. Pointers that point to two completely different objects in
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// memory never alias, regardless of the value of the Size component.
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_ALIAS_ANALYSIS_H
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#define LLVM_ANALYSIS_ALIAS_ANALYSIS_H
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#include "llvm/Support/CallSite.h"
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#include "llvm/System/IncludeFile.h"
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AliasAnalysis *AA; // Previous Alias Analysis to chain to.
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/// InitializeAliasAnalysis - Subclasses must call this method to initialize
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/// the AliasAnalysis interface before any other methods are called. This is
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/// typically called by the run* methods of these subclasses. This may be
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/// called multiple times.
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void InitializeAliasAnalysis(Pass *P);
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/// getAnalysisUsage - All alias analysis implementations should invoke this
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/// directly (using AliasAnalysis::getAnalysisUsage(AU)).
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virtual void getAnalysisUsage(AnalysisUsage &AU) const;
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static char ID; // Class identification, replacement for typeinfo
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AliasAnalysis() : TD(0), AA(0) {}
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virtual ~AliasAnalysis(); // We want to be subclassed
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/// getTargetData - Return a pointer to the current TargetData object, or
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/// null if no TargetData object is available.
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const TargetData *getTargetData() const { return TD; }
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/// getTypeStoreSize - Return the TargetData store size for the given type,
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/// if known, or a conservative value otherwise.
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unsigned getTypeStoreSize(const Type *Ty);
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//===--------------------------------------------------------------------===//
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/// Alias analysis result - Either we know for sure that it does not alias, we
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/// know for sure it must alias, or we don't know anything: The two pointers
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/// _might_ alias. This enum is designed so you can do things like:
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/// if (AA.alias(P1, P2)) { ... }
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/// to check to see if two pointers might alias.
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enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 };
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/// alias - The main low level interface to the alias analysis implementation.
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/// Returns a Result indicating whether the two pointers are aliased to each
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/// other. This is the interface that must be implemented by specific alias
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/// analysis implementations.
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virtual AliasResult alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size);
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/// isNoAlias - A trivial helper function to check to see if the specified
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/// pointers are no-alias.
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bool isNoAlias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size) {
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return alias(V1, V1Size, V2, V2Size) == NoAlias;
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/// pointsToConstantMemory - If the specified pointer is known to point into
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/// constant global memory, return true. This allows disambiguation of store
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/// instructions from constant pointers.
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virtual bool pointsToConstantMemory(const Value *P);
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//===--------------------------------------------------------------------===//
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/// Simple mod/ref information...
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/// ModRefResult - Represent the result of a mod/ref query. Mod and Ref are
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/// bits which may be or'd together.
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enum ModRefResult { NoModRef = 0, Ref = 1, Mod = 2, ModRef = 3 };
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/// ModRefBehavior - Summary of how a function affects memory in the program.
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/// Loads from constant globals are not considered memory accesses for this
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/// interface. Also, functions may freely modify stack space local to their
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/// invocation without having to report it through these interfaces.
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enum ModRefBehavior {
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// DoesNotAccessMemory - This function does not perform any non-local loads
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// or stores to memory.
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// This property corresponds to the GCC 'const' attribute.
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// AccessesArguments - This function accesses function arguments in well
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// known (possibly volatile) ways, but does not access any other memory.
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// Clients may use the Info parameter of getModRefBehavior to get specific
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// information about how pointer arguments are used.
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// AccessesArgumentsAndGlobals - This function has accesses function
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// arguments and global variables well known (possibly volatile) ways, but
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// does not access any other memory.
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// Clients may use the Info parameter of getModRefBehavior to get specific
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// information about how pointer arguments are used.
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AccessesArgumentsAndGlobals,
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// OnlyReadsMemory - This function does not perform any non-local stores or
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// volatile loads, but may read from any memory location.
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// This property corresponds to the GCC 'pure' attribute.
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// UnknownModRefBehavior - This indicates that the function could not be
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// classified into one of the behaviors above.
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UnknownModRefBehavior
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/// PointerAccessInfo - This struct is used to return results for pointers,
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/// globals, and the return value of a function.
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struct PointerAccessInfo {
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/// V - The value this record corresponds to. This may be an Argument for
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/// the function, a GlobalVariable, or null, corresponding to the return
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/// value for the function.
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/// ModRefInfo - Whether the pointer is loaded or stored to/from.
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ModRefResult ModRefInfo;
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/// AccessType - Specific fine-grained access information for the argument.
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/// If none of these classifications is general enough, the
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/// getModRefBehavior method should not return AccessesArguments*. If a
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/// record is not returned for a particular argument, the argument is never
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/// dead and never dereferenced.
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/// ScalarAccess - The pointer is dereferenced.
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/// ArrayAccess - The pointer is indexed through as an array of elements.
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/// ElementAccess ?? P->F only?
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/// CallsThrough - Indirect calls are made through the specified function
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/// getModRefBehavior - Return the behavior when calling the given call site.
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virtual ModRefBehavior getModRefBehavior(CallSite CS,
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std::vector<PointerAccessInfo> *Info = 0);
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/// getModRefBehavior - Return the behavior when calling the given function.
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/// For use when the call site is not known.
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virtual ModRefBehavior getModRefBehavior(Function *F,
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std::vector<PointerAccessInfo> *Info = 0);
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/// getModRefBehavior - Return the modref behavior of the intrinsic with the
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static ModRefBehavior getModRefBehavior(unsigned iid);
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/// doesNotAccessMemory - If the specified call is known to never read or
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/// write memory, return true. If the call only reads from known-constant
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/// memory, it is also legal to return true. Calls that unwind the stack
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/// are legal for this predicate.
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/// Many optimizations (such as CSE and LICM) can be performed on such calls
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/// without worrying about aliasing properties, and many calls have this
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/// property (e.g. calls to 'sin' and 'cos').
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/// This property corresponds to the GCC 'const' attribute.
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bool doesNotAccessMemory(CallSite CS) {
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return getModRefBehavior(CS) == DoesNotAccessMemory;
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/// doesNotAccessMemory - If the specified function is known to never read or
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/// write memory, return true. For use when the call site is not known.
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bool doesNotAccessMemory(Function *F) {
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return getModRefBehavior(F) == DoesNotAccessMemory;
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/// onlyReadsMemory - If the specified call is known to only read from
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/// non-volatile memory (or not access memory at all), return true. Calls
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/// that unwind the stack are legal for this predicate.
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/// This property allows many common optimizations to be performed in the
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/// absence of interfering store instructions, such as CSE of strlen calls.
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/// This property corresponds to the GCC 'pure' attribute.
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bool onlyReadsMemory(CallSite CS) {
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ModRefBehavior MRB = getModRefBehavior(CS);
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return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
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/// onlyReadsMemory - If the specified function is known to only read from
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/// non-volatile memory (or not access memory at all), return true. For use
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/// when the call site is not known.
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bool onlyReadsMemory(Function *F) {
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ModRefBehavior MRB = getModRefBehavior(F);
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return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory;
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/// getModRefInfo - Return information about whether or not an instruction may
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/// read or write memory specified by the pointer operand. An instruction
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/// that doesn't read or write memory may be trivially LICM'd for example.
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/// getModRefInfo (for call sites) - Return whether information about whether
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/// a particular call site modifies or reads the memory specified by the
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virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
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/// getModRefInfo - Return information about whether two call sites may refer
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/// to the same set of memory locations. This function returns NoModRef if
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/// the two calls refer to disjoint memory locations, Ref if CS1 reads memory
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/// written by CS2, Mod if CS1 writes to memory read or written by CS2, or
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/// ModRef if CS1 might read or write memory accessed by CS2.
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virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
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/// Convenience functions...
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ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size);
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ModRefResult getModRefInfo(StoreInst *S, Value *P, unsigned Size);
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ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) {
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return getModRefInfo(CallSite(C), P, Size);
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ModRefResult getModRefInfo(InvokeInst *I, Value *P, unsigned Size) {
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return getModRefInfo(CallSite(I), P, Size);
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ModRefResult getModRefInfo(VAArgInst* I, Value* P, unsigned Size) {
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return AliasAnalysis::ModRef;
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ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) {
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switch (I->getOpcode()) {
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case Instruction::VAArg: return getModRefInfo((VAArgInst*)I, P, Size);
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case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size);
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case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size);
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case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size);
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case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size);
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default: return NoModRef;
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//===--------------------------------------------------------------------===//
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/// Higher level methods for querying mod/ref information.
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/// canBasicBlockModify - Return true if it is possible for execution of the
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/// specified basic block to modify the value pointed to by Ptr.
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bool canBasicBlockModify(const BasicBlock &BB, const Value *P, unsigned Size);
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/// canInstructionRangeModify - Return true if it is possible for the
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/// execution of the specified instructions to modify the value pointed to by
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/// Ptr. The instructions to consider are all of the instructions in the
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/// range of [I1,I2] INCLUSIVE. I1 and I2 must be in the same basic block.
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bool canInstructionRangeModify(const Instruction &I1, const Instruction &I2,
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const Value *Ptr, unsigned Size);
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//===--------------------------------------------------------------------===//
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/// Methods that clients should call when they transform the program to allow
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/// alias analyses to update their internal data structures. Note that these
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/// methods may be called on any instruction, regardless of whether or not
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/// they have pointer-analysis implications.
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/// deleteValue - This method should be called whenever an LLVM Value is
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/// deleted from the program, for example when an instruction is found to be
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/// redundant and is eliminated.
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virtual void deleteValue(Value *V);
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/// copyValue - This method should be used whenever a preexisting value in the
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/// program is copied or cloned, introducing a new value. Note that analysis
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/// implementations should tolerate clients that use this method to introduce
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/// the same value multiple times: if the analysis already knows about a
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/// value, it should ignore the request.
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virtual void copyValue(Value *From, Value *To);
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/// replaceWithNewValue - This method is the obvious combination of the two
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/// above, and it provided as a helper to simplify client code.
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void replaceWithNewValue(Value *Old, Value *New) {
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/// isNoAliasCall - Return true if this pointer is returned by a noalias
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bool isNoAliasCall(const Value *V);
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/// isIdentifiedObject - Return true if this pointer refers to a distinct and
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/// identifiable object. This returns true for:
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/// Global Variables and Functions (but not Global Aliases)
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/// Allocas and Mallocs
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/// ByVal and NoAlias Arguments
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bool isIdentifiedObject(const Value *V);
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} // End llvm namespace
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// Because of the way .a files work, we must force the BasicAA implementation to
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// be pulled in if the AliasAnalysis header is included. Otherwise we run
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// the risk of AliasAnalysis being used, but the default implementation not
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// being linked into the tool that uses it.
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FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis)
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FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis)