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Diffstat (limited to 'include/llvm/Analysis/AliasAnalysis.h')
| -rw-r--r-- | include/llvm/Analysis/AliasAnalysis.h | 363 |
1 files changed, 363 insertions, 0 deletions
diff --git a/include/llvm/Analysis/AliasAnalysis.h b/include/llvm/Analysis/AliasAnalysis.h new file mode 100644 index 0000000000000..ba040e1393bf3 --- /dev/null +++ b/include/llvm/Analysis/AliasAnalysis.h @@ -0,0 +1,363 @@ +//===- 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 |