llvm-6502/include/llvm/Analysis/AliasAnalysis.h
Dan Gohman 3311a1f8f0 Fix a post-RA scheduling dependency bug.
If a MachineInstr doesn't have a memoperand but has an opcode that
is known to load or store, assume its memory reference may alias
*anything*, including stack slots which the compiler completely
controls.

To partially compensate for this, teach the ScheduleDAG building
code to do basic getUnderlyingValue analysis. This greatly
reduces the number of instructions that require restrictive
dependencies. This code will need to be revisited when we start
doing real alias analysis, but it should suffice for now.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@63370 91177308-0d34-0410-b5e6-96231b3b80d8
2009-01-30 02:49:14 +00:00

363 lines
15 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. 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
// non-volatile and well known 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 in non-volatile and well-known 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.
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.
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;
protected:
/// 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);
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);
}
};
/// isIdentifiedObject - Return true if this pointer refers to a distinct and
/// identifiable object.
///
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