llvm-mirror/lib/Analysis/AliasAnalysis.cpp
Chris Lattner 1637c0e720 use the new isNoAlias method to simplify some code, only do an escaping check if
we have a non-constant pointer.  Constant pointers can't be local.

llvm-svn: 89665
2009-11-23 16:46:41 +00:00

247 lines
9.0 KiB
C++

//===- AliasAnalysis.cpp - Generic Alias Analysis Interface Implementation -==//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the generic AliasAnalysis interface which is used as the
// common interface used by all clients and implementations of alias analysis.
//
// This file also implements the default version of the AliasAnalysis interface
// that is to be used when no other implementation is specified. This does some
// simple tests that detect obvious cases: two different global pointers cannot
// alias, a global cannot alias a malloc, two different mallocs cannot alias,
// etc.
//
// This alias analysis implementation really isn't very good for anything, but
// it is very fast, and makes a nice clean default implementation. Because it
// handles lots of little corner cases, other, more complex, alias analysis
// implementations may choose to rely on this pass to resolve these simple and
// easy cases.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Pass.h"
#include "llvm/BasicBlock.h"
#include "llvm/Function.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Instructions.h"
#include "llvm/Type.h"
#include "llvm/Target/TargetData.h"
using namespace llvm;
// Register the AliasAnalysis interface, providing a nice name to refer to.
static RegisterAnalysisGroup<AliasAnalysis> Z("Alias Analysis");
char AliasAnalysis::ID = 0;
//===----------------------------------------------------------------------===//
// Default chaining methods
//===----------------------------------------------------------------------===//
AliasAnalysis::AliasResult
AliasAnalysis::alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
return AA->alias(V1, V1Size, V2, V2Size);
}
bool AliasAnalysis::pointsToConstantMemory(const Value *P) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
return AA->pointsToConstantMemory(P);
}
void AliasAnalysis::deleteValue(Value *V) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
AA->deleteValue(V);
}
void AliasAnalysis::copyValue(Value *From, Value *To) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
AA->copyValue(From, To);
}
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
// FIXME: we can do better.
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
return AA->getModRefInfo(CS1, CS2);
}
//===----------------------------------------------------------------------===//
// AliasAnalysis non-virtual helper method implementation
//===----------------------------------------------------------------------===//
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(LoadInst *L, Value *P, unsigned Size) {
return alias(L->getOperand(0), getTypeStoreSize(L->getType()),
P, Size) ? Ref : NoModRef;
}
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(StoreInst *S, Value *P, unsigned Size) {
// If the stored address cannot alias the pointer in question, then the
// pointer cannot be modified by the store.
if (!alias(S->getOperand(1),
getTypeStoreSize(S->getOperand(0)->getType()), P, Size))
return NoModRef;
// If the pointer is a pointer to constant memory, then it could not have been
// modified by this store.
return pointsToConstantMemory(P) ? NoModRef : Mod;
}
AliasAnalysis::ModRefBehavior
AliasAnalysis::getModRefBehavior(CallSite CS,
std::vector<PointerAccessInfo> *Info) {
if (CS.doesNotAccessMemory())
// Can't do better than this.
return DoesNotAccessMemory;
ModRefBehavior MRB = getModRefBehavior(CS.getCalledFunction(), Info);
if (MRB != DoesNotAccessMemory && CS.onlyReadsMemory())
return OnlyReadsMemory;
return MRB;
}
AliasAnalysis::ModRefBehavior
AliasAnalysis::getModRefBehavior(Function *F,
std::vector<PointerAccessInfo> *Info) {
if (F) {
if (F->doesNotAccessMemory())
// Can't do better than this.
return DoesNotAccessMemory;
if (F->onlyReadsMemory())
return OnlyReadsMemory;
if (unsigned id = F->getIntrinsicID()) {
#define GET_INTRINSIC_MODREF_BEHAVIOR
#include "llvm/Intrinsics.gen"
#undef GET_INTRINSIC_MODREF_BEHAVIOR
}
}
return UnknownModRefBehavior;
}
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
ModRefBehavior MRB = getModRefBehavior(CS);
if (MRB == DoesNotAccessMemory)
return NoModRef;
ModRefResult Mask = ModRef;
if (MRB == OnlyReadsMemory)
Mask = Ref;
else if (MRB == AliasAnalysis::AccessesArguments) {
bool doesAlias = false;
for (CallSite::arg_iterator AI = CS.arg_begin(), AE = CS.arg_end();
AI != AE; ++AI)
if (!isNoAlias(*AI, ~0U, P, Size)) {
doesAlias = true;
break;
}
if (!doesAlias)
return NoModRef;
}
if (!AA) return Mask;
// If P points to a constant memory location, the call definitely could not
// modify the memory location.
if ((Mask & Mod) && AA->pointsToConstantMemory(P))
Mask = ModRefResult(Mask & ~Mod);
return ModRefResult(Mask & AA->getModRefInfo(CS, P, Size));
}
// AliasAnalysis destructor: DO NOT move this to the header file for
// AliasAnalysis or else clients of the AliasAnalysis class may not depend on
// the AliasAnalysis.o file in the current .a file, causing alias analysis
// support to not be included in the tool correctly!
//
AliasAnalysis::~AliasAnalysis() {}
/// InitializeAliasAnalysis - Subclasses must call this method to initialize the
/// AliasAnalysis interface before any other methods are called.
///
void AliasAnalysis::InitializeAliasAnalysis(Pass *P) {
TD = P->getAnalysisIfAvailable<TargetData>();
AA = &P->getAnalysis<AliasAnalysis>();
}
// getAnalysisUsage - All alias analysis implementations should invoke this
// directly (using AliasAnalysis::getAnalysisUsage(AU)).
void AliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<AliasAnalysis>(); // All AA's chain
}
/// getTypeStoreSize - Return the TargetData store size for the given type,
/// if known, or a conservative value otherwise.
///
unsigned AliasAnalysis::getTypeStoreSize(const Type *Ty) {
return TD ? TD->getTypeStoreSize(Ty) : ~0u;
}
/// canBasicBlockModify - Return true if it is possible for execution of the
/// specified basic block to modify the value pointed to by Ptr.
///
bool AliasAnalysis::canBasicBlockModify(const BasicBlock &BB,
const Value *Ptr, unsigned Size) {
return canInstructionRangeModify(BB.front(), BB.back(), Ptr, 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 AliasAnalysis::canInstructionRangeModify(const Instruction &I1,
const Instruction &I2,
const Value *Ptr, unsigned Size) {
assert(I1.getParent() == I2.getParent() &&
"Instructions not in same basic block!");
BasicBlock::iterator I = const_cast<Instruction*>(&I1);
BasicBlock::iterator E = const_cast<Instruction*>(&I2);
++E; // Convert from inclusive to exclusive range.
for (; I != E; ++I) // Check every instruction in range
if (getModRefInfo(I, const_cast<Value*>(Ptr), Size) & Mod)
return true;
return false;
}
/// isNoAliasCall - Return true if this pointer is returned by a noalias
/// function.
bool llvm::isNoAliasCall(const Value *V) {
if (isa<CallInst>(V) || isa<InvokeInst>(V))
return CallSite(const_cast<Instruction*>(cast<Instruction>(V)))
.paramHasAttr(0, Attribute::NoAlias);
return false;
}
/// 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 llvm::isIdentifiedObject(const Value *V) {
if (isa<AllocaInst>(V) || isNoAliasCall(V))
return true;
if (isa<GlobalValue>(V) && !isa<GlobalAlias>(V))
return true;
if (const Argument *A = dyn_cast<Argument>(V))
return A->hasNoAliasAttr() || A->hasByValAttr();
return false;
}
// Because of the way .a files work, we must force the BasicAA implementation to
// be pulled in if the AliasAnalysis classes are pulled in. Otherwise we run
// the risk of AliasAnalysis being used, but the default implementation not
// being linked into the tool that uses it.
DEFINING_FILE_FOR(AliasAnalysis)