//===- 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 represents memory as a (Pointer, Size) pair. The Pointer component // specifies the base memory address of the region, the Size specifies how large // of an area is being queried. If Size is 0, two pointers only alias if they // are exactly equal. If size is greater than zero, but small, the two pointers // alias if the areas pointed to overlap. If the size is very large (ie, ~0U), // then the two pointers alias if they may be pointing to components of the same // memory object. Pointers that point to two completely different objects in // memory never alias, regardless of the value of the Size component. // //===----------------------------------------------------------------------===// #ifndef LLVM_ANALYSIS_ALIAS_ANALYSIS_H #define LLVM_ANALYSIS_ALIAS_ANALYSIS_H #include "llvm/Support/CallSite.h" #include "llvm/System/IncludeFile.h" #include <vector> namespace llvm { class LoadInst; class StoreInst; class VAArgInst; class TargetData; class Pass; class AnalysisUsage; class AliasAnalysis { protected: const TargetData *TD; AliasAnalysis *AA; // Previous Alias Analysis to chain to. /// 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)) to make sure that /// TargetData is required by the pass. 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 /// getTargetData - Every alias analysis implementation depends on the size of /// data items in the current Target. This provides a uniform way to handle /// it. /// const TargetData &getTargetData() const { return *TD; } //===--------------------------------------------------------------------===// /// Alias Queries... /// /// 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. /// enum AliasResult { NoAlias = 0, MayAlias = 1, MustAlias = 2 }; /// alias - The main low level interface to the alias analysis implementation. /// Returns a Result 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 Value *V1, unsigned V1Size, const Value *V2, unsigned V2Size); /// getMustAliases - If there are any pointers known that must alias this /// pointer, return them now. This allows alias-set based alias analyses to /// perform a form a value numbering (which is exposed by load-vn). If an /// alias analysis supports this, it should ADD any must aliased pointers to /// the specified vector. /// virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals); /// pointsToConstantMemory - If the specified pointer is known to point into /// constant global memory, return true. This allows disambiguation of store /// instructions from constant pointers. /// virtual bool pointsToConstantMemory(const Value *P); //===--------------------------------------------------------------------===// /// 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 }; /// 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. DoesNotAccessMemory, // AccessesArguments - This function accesses function arguments in well // known (possibly volatile) ways, but does not access any other memory. // // Clients may use the Info parameter of getModRefBehavior to get specific // information about how pointer arguments are used. AccessesArguments, // AccessesArgumentsAndGlobals - This function has accesses function // arguments and global variables well known (possibly volatile) ways, but // does not access any other memory. // // Clients may use the Info parameter of getModRefBehavior to get specific // information about how pointer arguments are used. AccessesArgumentsAndGlobals, // 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. OnlyReadsMemory, // UnknownModRefBehavior - This indicates that the function could not be // classified into one of the behaviors above. UnknownModRefBehavior }; /// PointerAccessInfo - This struct is used to return results for pointers, /// globals, and the return value of a function. struct PointerAccessInfo { /// V - The value this record corresponds to. This may be an Argument for /// the function, a GlobalVariable, or null, corresponding to the return /// value for the function. Value *V; /// ModRefInfo - Whether the pointer is loaded or stored to/from. /// ModRefResult ModRefInfo; /// AccessType - Specific fine-grained access information for the argument. /// If none of these classifications is general enough, the /// getModRefBehavior method should not return AccessesArguments*. If a /// record is not returned for a particular argument, the argument is never /// dead and never dereferenced. enum AccessType { /// ScalarAccess - The pointer is dereferenced. /// ScalarAccess, /// ArrayAccess - The pointer is indexed through as an array of elements. /// ArrayAccess, /// ElementAccess ?? P->F only? /// CallsThrough - Indirect calls are made through the specified function /// pointer. CallsThrough }; }; /// getModRefBehavior - Return the behavior when calling the given call site. virtual ModRefBehavior getModRefBehavior(CallSite CS, std::vector<PointerAccessInfo> *Info = 0); /// getModRefBehavior - Return the behavior when calling the given function. /// For use when the call site is not known. virtual ModRefBehavior getModRefBehavior(Function *F, std::vector<PointerAccessInfo> *Info = 0); /// 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(CallSite 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(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(CallSite CS) { ModRefBehavior MRB = getModRefBehavior(CS); return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; } /// 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(Function *F) { ModRefBehavior MRB = getModRefBehavior(F); return MRB == DoesNotAccessMemory || MRB == OnlyReadsMemory; } /// getModRefInfo - Return information about whether or not an instruction may /// read or write memory specified by the pointer operand. An instruction /// that doesn't read or write memory may be trivially LICM'd for example. /// getModRefInfo (for call sites) - Return whether information about whether /// a particular call site modifies or reads the memory specified by the /// pointer. /// virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); /// getModRefInfo - Return information about whether two call sites may refer /// to the same set of memory locations. This function returns NoModRef if /// the two calls refer to disjoint memory locations, Ref if CS1 reads memory /// written by CS2, Mod if CS1 writes to memory read or written by CS2, or /// ModRef if CS1 might read or write memory accessed by CS2. /// virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2); /// hasNoModRefInfoForCalls - Return true if the analysis has no mod/ref /// information for pairs of function calls (other than "pure" and "const" /// functions). This can be used by clients to avoid many pointless queries. /// Remember that if you override this and chain to another analysis, you must /// make sure that it doesn't have mod/ref info either. /// virtual bool hasNoModRefInfoForCalls() const; public: /// Convenience functions... ModRefResult getModRefInfo(LoadInst *L, Value *P, unsigned Size); ModRefResult getModRefInfo(StoreInst *S, Value *P, unsigned Size); ModRefResult getModRefInfo(CallInst *C, Value *P, unsigned Size) { return getModRefInfo(CallSite(C), P, Size); } ModRefResult getModRefInfo(InvokeInst *I, Value *P, unsigned Size) { return getModRefInfo(CallSite(I), P, Size); } ModRefResult getModRefInfo(VAArgInst* I, Value* P, unsigned Size) { return AliasAnalysis::ModRef; } ModRefResult getModRefInfo(Instruction *I, Value *P, unsigned Size) { switch (I->getOpcode()) { case Instruction::VAArg: return getModRefInfo((VAArgInst*)I, P, Size); case Instruction::Load: return getModRefInfo((LoadInst*)I, P, Size); case Instruction::Store: return getModRefInfo((StoreInst*)I, P, Size); case Instruction::Call: return getModRefInfo((CallInst*)I, P, Size); case Instruction::Invoke: return getModRefInfo((InvokeInst*)I, P, Size); default: return NoModRef; } } //===--------------------------------------------------------------------===// /// 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 Value *P, unsigned 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 Value *Ptr, unsigned 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); /// 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); } }; /// 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 /// Allocas and Mallocs /// ByVal and NoAlias Arguments /// NoAlias returns /// bool isIdentifiedObject(const Value *V); } // End llvm namespace // Because of the way .a files work, we must force the BasicAA implementation to // be pulled in if the AliasAnalysis header is included. Otherwise we run // the risk of AliasAnalysis being used, but the default implementation not // being linked into the tool that uses it. FORCE_DEFINING_FILE_TO_BE_LINKED(AliasAnalysis) FORCE_DEFINING_FILE_TO_BE_LINKED(BasicAliasAnalysis) #endif