//===- llvm/Analysis/AliasAnalysis.h - Alias Analysis Interface -*- C++ -*-===//
//
+// The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and 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.
+// 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
-class Value;
-class CallInst;
-class InvokeInst;
-class BasicBlock;
-class Instruction;
-
-struct AliasAnalysis {
-
- // 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 Result { 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 Result alias(const Value *V1, const Value *V2) const = 0;
-
- // canCallModify - Return a Result that indicates whether the specified
- // function call can modify the memory location pointed to by Ptr.
- //
- virtual Result canCallModify(const CallInst &CI, const Value *Ptr) const = 0;
-
- // canInvokeModify - Return a Result that indicates whether the specified
- // function invoke can modify the memory location pointed to by Ptr.
- //
- virtual Result canInvokeModify(const InvokeInst &I, const Value *Ptr) const=0;
-
- // 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 *Ptr) const;
-
- // 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) const;
+#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
+ // non-volatile and well known ways, but does not access any other memory.
+ //
+ // Clients may call getArgumentAccesses to get specific information about
+ // how pointer arguments are used.
+ AccessesArguments,
+
+ // AccessesArgumentsAndGlobals - This function has accesses function
+ // arguments and global variables in non-volatile and well-known ways, but
+ // does not access any other memory.
+ //
+ // Clients may call getArgumentAccesses to get specific information about
+ // how pointer arguments and globals 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 of the specified function if
+ /// called from the specified call site. The call site may be null in which
+ /// case the most generic behavior of this function should be returned.
+ virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
+ std::vector<PointerAccessInfo> *Info = 0);
+
+ /// doesNotAccessMemory - If the specified function is known to never read or
+ /// write memory, return true. If the function only reads from known-constant
+ /// memory, it is also legal to return true. Functions that unwind the stack
+ /// are not legal for this predicate.
+ ///
+ /// Many optimizations (such as CSE and LICM) can be performed on calls to it,
+ /// without worrying about aliasing properties, and many functions have this
+ /// property (e.g. 'sin' and 'cos').
+ ///
+ /// This property corresponds to the GCC 'const' attribute.
+ ///
+ bool doesNotAccessMemory(Function *F) {
+ return getModRefBehavior(F, CallSite()) == DoesNotAccessMemory;
+ }
+
+ /// onlyReadsMemory - If the specified function is known to only read from
+ /// non-volatile memory (or not access memory at all), return true. Functions
+ /// that unwind the stack are not 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(Function *F) {
+ /// FIXME: If the analysis returns more precise info, we can reduce it to
+ /// this.
+ ModRefBehavior MRB = getModRefBehavior(F, CallSite());
+ 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;
+
+ /// 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);
+ }
};
+} // 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
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