llvm-6502/include/llvm/Analysis/AliasAnalysis.h
Dan Gohman 39429e2b51 Update the descriptions of NoModRef and ModRef to be consistent
with the descriptions of Mod and Ref.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112557 91177308-0d34-0410-b5e6-96231b3b80d8
2010-08-30 23:47:24 +00:00

334 lines
14 KiB
C++

//===- 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, or UnknownSize if the size is not known.
// 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;
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 unsigned const UnknownSize = ~0u;
/// 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.
///
unsigned getTypeStoreSize(const Type *Ty);
//===--------------------------------------------------------------------===//
/// 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.
///
/// See docs/AliasAnalysis.html for more information on the specific meanings
/// of these values.
///
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);
/// alias - A convenience wrapper for the case where the sizes are unknown.
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 Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size) {
return alias(V1, V1Size, V2, V2Size) == NoAlias;
}
/// 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.
AccessesArguments,
// AccessesArgumentsAndGlobals - This function has accesses function
// arguments and global variables well known (possibly volatile) ways, but
// does not access any other memory.
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
};
/// 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);
/// getIntrinsicModRefBehavior - Return the modref behavior of the intrinsic
/// with the given id. Most clients won't need this, because the regular
/// getModRefBehavior incorporates this information.
static ModRefBehavior getIntrinsicModRefBehavior(unsigned iid);
/// 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) {
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(const 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(ImmutableCallSite CS,
const Value *P, unsigned 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);
public:
/// Convenience functions...
ModRefResult getModRefInfo(const LoadInst *L, const Value *P, unsigned Size);
ModRefResult getModRefInfo(const StoreInst *S, const Value *P, unsigned Size);
ModRefResult getModRefInfo(const VAArgInst* I, const Value* P, unsigned Size);
ModRefResult getModRefInfo(const CallInst *C, const Value *P, unsigned Size) {
return getModRefInfo(ImmutableCallSite(C), P, Size);
}
ModRefResult getModRefInfo(const InvokeInst *I,
const Value *P, unsigned Size) {
return getModRefInfo(ImmutableCallSite(I), P, Size);
}
ModRefResult getModRefInfo(const Instruction *I,
const Value *P, unsigned Size) {
switch (I->getOpcode()) {
case Instruction::VAArg: return getModRefInfo((const VAArgInst*)I, P,Size);
case Instruction::Load: return getModRefInfo((const LoadInst*)I, P, Size);
case Instruction::Store: return getModRefInfo((const StoreInst*)I, P,Size);
case Instruction::Call: return getModRefInfo((const CallInst*)I, P, Size);
case Instruction::Invoke: return getModRefInfo((const 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 (but not Global Aliases)
/// 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