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llvm-mirror/lib/Analysis/BasicAliasAnalysis.cpp
Reid Spencer 560366562b For PR780: 
1. Fix the macros in IncludeFile.h to put everything in the llvm namespace
2. Replace the previous explicit mechanism in all the .h and .cpp files
   with the macros in IncludeFile.h
This gets us a consistent mechanism throughout LLVM for ensuring linkage.
Next step is to make sure its used in enough places.

llvm-svn: 28715
2006-06-07 22:00:26 +00:00

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//===- BasicAliasAnalysis.cpp - Local Alias Analysis Impl -----------------===//
//
// 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 default implementation of the Alias Analysis interface
// that simply implements a few identities (two different globals cannot alias,
// etc), but otherwise does no analysis.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
#include "llvm/Pass.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include <algorithm>
using namespace llvm;
namespace {
/// NoAA - This class implements the -no-aa pass, which always returns "I
/// don't know" for alias queries. NoAA is unlike other alias analysis
/// implementations, in that it does not chain to a previous analysis. As
/// such it doesn't follow many of the rules that other alias analyses must.
///
struct NoAA : public ImmutablePass, public AliasAnalysis {
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<TargetData>();
}
virtual void initializePass() {
TD = &getAnalysis<TargetData>();
}
virtual AliasResult alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size) {
return MayAlias;
}
virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
std::vector<PointerAccessInfo> *Info) {
return UnknownModRefBehavior;
}
virtual void getArgumentAccesses(Function *F, CallSite CS,
std::vector<PointerAccessInfo> &Info) {
assert(0 && "This method may not be called on this function!");
}
virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
virtual bool pointsToConstantMemory(const Value *P) { return false; }
virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
return ModRef;
}
virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
return ModRef;
}
virtual bool hasNoModRefInfoForCalls() const { return true; }
virtual void deleteValue(Value *V) {}
virtual void copyValue(Value *From, Value *To) {}
};
// Register this pass...
RegisterOpt<NoAA>
U("no-aa", "No Alias Analysis (always returns 'may' alias)");
// Declare that we implement the AliasAnalysis interface
RegisterAnalysisGroup<AliasAnalysis, NoAA> V;
} // End of anonymous namespace
ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
namespace {
/// BasicAliasAnalysis - This is the default alias analysis implementation.
/// Because it doesn't chain to a previous alias analysis (like -no-aa), it
/// derives from the NoAA class.
struct BasicAliasAnalysis : public NoAA {
AliasResult alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size);
ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
return NoAA::getModRefInfo(CS1,CS2);
}
/// hasNoModRefInfoForCalls - We can provide mod/ref information against
/// non-escaping allocations.
virtual bool hasNoModRefInfoForCalls() const { return false; }
/// pointsToConstantMemory - Chase pointers until we find a (constant
/// global) or not.
bool pointsToConstantMemory(const Value *P);
virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
std::vector<PointerAccessInfo> *Info);
private:
// CheckGEPInstructions - Check two GEP instructions with known
// must-aliasing base pointers. This checks to see if the index expressions
// preclude the pointers from aliasing...
AliasResult
CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
unsigned G1Size,
const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
unsigned G2Size);
};
// Register this pass...
RegisterOpt<BasicAliasAnalysis>
X("basicaa", "Basic Alias Analysis (default AA impl)");
// Declare that we implement the AliasAnalysis interface
RegisterAnalysisGroup<AliasAnalysis, BasicAliasAnalysis, true> Y;
} // End of anonymous namespace
ImmutablePass *llvm::createBasicAliasAnalysisPass() {
return new BasicAliasAnalysis();
}
// hasUniqueAddress - Return true if the specified value points to something
// with a unique, discernable, address.
static inline bool hasUniqueAddress(const Value *V) {
return isa<GlobalValue>(V) || isa<AllocationInst>(V);
}
// getUnderlyingObject - This traverses the use chain to figure out what object
// the specified value points to. If the value points to, or is derived from, a
// unique object or an argument, return it.
static const Value *getUnderlyingObject(const Value *V) {
if (!isa<PointerType>(V->getType())) return 0;
// If we are at some type of object... return it.
if (hasUniqueAddress(V) || isa<Argument>(V)) return V;
// Traverse through different addressing mechanisms...
if (const Instruction *I = dyn_cast<Instruction>(V)) {
if (isa<CastInst>(I) || isa<GetElementPtrInst>(I))
return getUnderlyingObject(I->getOperand(0));
} else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
if (CE->getOpcode() == Instruction::Cast ||
CE->getOpcode() == Instruction::GetElementPtr)
return getUnderlyingObject(CE->getOperand(0));
} else if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
return GV;
}
return 0;
}
static const User *isGEP(const Value *V) {
if (isa<GetElementPtrInst>(V) ||
(isa<ConstantExpr>(V) &&
cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
return cast<User>(V);
return 0;
}
static const Value *GetGEPOperands(const Value *V, std::vector<Value*> &GEPOps){
assert(GEPOps.empty() && "Expect empty list to populate!");
GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
cast<User>(V)->op_end());
// Accumulate all of the chained indexes into the operand array
V = cast<User>(V)->getOperand(0);
while (const User *G = isGEP(V)) {
if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
!cast<Constant>(GEPOps[0])->isNullValue())
break; // Don't handle folding arbitrary pointer offsets yet...
GEPOps.erase(GEPOps.begin()); // Drop the zero index
GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
V = G->getOperand(0);
}
return V;
}
/// pointsToConstantMemory - Chase pointers until we find a (constant
/// global) or not.
bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
if (const Value *V = getUnderlyingObject(P))
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
return GV->isConstant();
return false;
}
static bool AddressMightEscape(const Value *V) {
for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
UI != E; ++UI) {
const Instruction *I = cast<Instruction>(*UI);
switch (I->getOpcode()) {
case Instruction::Load: break;
case Instruction::Store:
if (I->getOperand(0) == V)
return true; // Escapes if the pointer is stored.
break;
case Instruction::GetElementPtr:
if (AddressMightEscape(I)) return true;
break;
case Instruction::Cast:
if (!isa<PointerType>(I->getType()))
return true;
if (AddressMightEscape(I)) return true;
break;
case Instruction::Ret:
// If returned, the address will escape to calling functions, but no
// callees could modify it.
break;
default:
return true;
}
}
return false;
}
// getModRefInfo - Check to see if the specified callsite can clobber the
// specified memory object. Since we only look at local properties of this
// function, we really can't say much about this query. We do, however, use
// simple "address taken" analysis on local objects.
//
AliasAnalysis::ModRefResult
BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
if (!isa<Constant>(P))
if (const AllocationInst *AI =
dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) {
// Okay, the pointer is to a stack allocated object. If we can prove that
// the pointer never "escapes", then we know the call cannot clobber it,
// because it simply can't get its address.
if (!AddressMightEscape(AI))
return NoModRef;
// If this is a tail call and P points to a stack location, we know that
// the tail call cannot access or modify the local stack.
if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
if (CI->isTailCall() && isa<AllocaInst>(AI))
return NoModRef;
}
// The AliasAnalysis base class has some smarts, lets use them.
return AliasAnalysis::getModRefInfo(CS, P, Size);
}
// alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
// as array references. Note that this function is heavily tail recursive.
// Hopefully we have a smart C++ compiler. :)
//
AliasAnalysis::AliasResult
BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size) {
// Strip off any constant expression casts if they exist
if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
if (CE->getOpcode() == Instruction::Cast &&
isa<PointerType>(CE->getOperand(0)->getType()))
V1 = CE->getOperand(0);
if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
if (CE->getOpcode() == Instruction::Cast &&
isa<PointerType>(CE->getOperand(0)->getType()))
V2 = CE->getOperand(0);
// Are we checking for alias of the same value?
if (V1 == V2) return MustAlias;
if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
V1->getType() != Type::LongTy && V2->getType() != Type::LongTy)
return NoAlias; // Scalars cannot alias each other
// Strip off cast instructions...
if (const Instruction *I = dyn_cast<CastInst>(V1))
if (isa<PointerType>(I->getOperand(0)->getType()))
return alias(I->getOperand(0), V1Size, V2, V2Size);
if (const Instruction *I = dyn_cast<CastInst>(V2))
if (isa<PointerType>(I->getOperand(0)->getType()))
return alias(V1, V1Size, I->getOperand(0), V2Size);
// Figure out what objects these things are pointing to if we can...
const Value *O1 = getUnderlyingObject(V1);
const Value *O2 = getUnderlyingObject(V2);
// Pointing at a discernible object?
if (O1) {
if (O2) {
if (isa<Argument>(O1)) {
// Incoming argument cannot alias locally allocated object!
if (isa<AllocationInst>(O2)) return NoAlias;
// Otherwise, nothing is known...
} else if (isa<Argument>(O2)) {
// Incoming argument cannot alias locally allocated object!
if (isa<AllocationInst>(O1)) return NoAlias;
// Otherwise, nothing is known...
} else if (O1 != O2) {
// If they are two different objects, we know that we have no alias...
return NoAlias;
}
// If they are the same object, they we can look at the indexes. If they
// index off of the object is the same for both pointers, they must alias.
// If they are provably different, they must not alias. Otherwise, we
// can't tell anything.
}
if (!isa<Argument>(O1) && isa<ConstantPointerNull>(V2))
return NoAlias; // Unique values don't alias null
if (isa<GlobalVariable>(O1) ||
(isa<AllocationInst>(O1) &&
!cast<AllocationInst>(O1)->isArrayAllocation()))
if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
// If the size of the other access is larger than the total size of the
// global/alloca/malloc, it cannot be accessing the global (it's
// undefined to load or store bytes before or after an object).
const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
if (GlobalSize < V2Size && V2Size != ~0U)
return NoAlias;
}
}
if (O2) {
if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
return NoAlias; // Unique values don't alias null
if (isa<GlobalVariable>(O2) ||
(isa<AllocationInst>(O2) &&
!cast<AllocationInst>(O2)->isArrayAllocation()))
if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
// If the size of the other access is larger than the total size of the
// global/alloca/malloc, it cannot be accessing the object (it's
// undefined to load or store bytes before or after an object).
const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
if (GlobalSize < V1Size && V1Size != ~0U)
return NoAlias;
}
}
// If we have two gep instructions with must-alias'ing base pointers, figure
// out if the indexes to the GEP tell us anything about the derived pointer.
// Note that we also handle chains of getelementptr instructions as well as
// constant expression getelementptrs here.
//
if (isGEP(V1) && isGEP(V2)) {
// Drill down into the first non-gep value, to test for must-aliasing of
// the base pointers.
const Value *BasePtr1 = V1, *BasePtr2 = V2;
do {
BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
} while (isGEP(BasePtr1) &&
cast<User>(BasePtr1)->getOperand(1) ==
Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
do {
BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
} while (isGEP(BasePtr2) &&
cast<User>(BasePtr2)->getOperand(1) ==
Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
// Do the base pointers alias?
AliasResult BaseAlias = alias(BasePtr1, V1Size, BasePtr2, V2Size);
if (BaseAlias == NoAlias) return NoAlias;
if (BaseAlias == MustAlias) {
// If the base pointers alias each other exactly, check to see if we can
// figure out anything about the resultant pointers, to try to prove
// non-aliasing.
// Collect all of the chained GEP operands together into one simple place
std::vector<Value*> GEP1Ops, GEP2Ops;
BasePtr1 = GetGEPOperands(V1, GEP1Ops);
BasePtr2 = GetGEPOperands(V2, GEP2Ops);
// If GetGEPOperands were able to fold to the same must-aliased pointer,
// do the comparison.
if (BasePtr1 == BasePtr2) {
AliasResult GAlias =
CheckGEPInstructions(BasePtr1->getType(), GEP1Ops, V1Size,
BasePtr2->getType(), GEP2Ops, V2Size);
if (GAlias != MayAlias)
return GAlias;
}
}
}
// Check to see if these two pointers are related by a getelementptr
// instruction. If one pointer is a GEP with a non-zero index of the other
// pointer, we know they cannot alias.
//
if (isGEP(V2)) {
std::swap(V1, V2);
std::swap(V1Size, V2Size);
}
if (V1Size != ~0U && V2Size != ~0U)
if (const User *GEP = isGEP(V1)) {
std::vector<Value*> GEPOperands;
const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
if (R == MustAlias) {
// If there is at least one non-zero constant index, we know they cannot
// alias.
bool ConstantFound = false;
bool AllZerosFound = true;
for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
if (!C->isNullValue()) {
ConstantFound = true;
AllZerosFound = false;
break;
}
} else {
AllZerosFound = false;
}
// If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
// the ptr, the end result is a must alias also.
if (AllZerosFound)
return MustAlias;
if (ConstantFound) {
if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
return NoAlias;
// Otherwise we have to check to see that the distance is more than
// the size of the argument... build an index vector that is equal to
// the arguments provided, except substitute 0's for any variable
// indexes we find...
if (cast<PointerType>(
BasePtr->getType())->getElementType()->isSized()) {
for (unsigned i = 0; i != GEPOperands.size(); ++i)
if (!isa<ConstantInt>(GEPOperands[i]))
GEPOperands[i] =
Constant::getNullValue(GEPOperands[i]->getType());
int64_t Offset =
getTargetData().getIndexedOffset(BasePtr->getType(), GEPOperands);
if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
return NoAlias;
}
}
}
}
return MayAlias;
}
static bool ValuesEqual(Value *V1, Value *V2) {
if (V1->getType() == V2->getType())
return V1 == V2;
if (Constant *C1 = dyn_cast<Constant>(V1))
if (Constant *C2 = dyn_cast<Constant>(V2)) {
// Sign extend the constants to long types.
C1 = ConstantExpr::getSignExtend(C1, Type::LongTy);
C2 = ConstantExpr::getSignExtend(C2, Type::LongTy);
return C1 == C2;
}
return false;
}
/// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
/// base pointers. This checks to see if the index expressions preclude the
/// pointers from aliasing...
AliasAnalysis::AliasResult BasicAliasAnalysis::
CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
unsigned G1S,
const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
unsigned G2S) {
// We currently can't handle the case when the base pointers have different
// primitive types. Since this is uncommon anyway, we are happy being
// extremely conservative.
if (BasePtr1Ty != BasePtr2Ty)
return MayAlias;
const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
// Find the (possibly empty) initial sequence of equal values... which are not
// necessarily constants.
unsigned NumGEP1Operands = GEP1Ops.size(), NumGEP2Operands = GEP2Ops.size();
unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
unsigned UnequalOper = 0;
while (UnequalOper != MinOperands &&
ValuesEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
// Advance through the type as we go...
++UnequalOper;
if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
else {
// If all operands equal each other, then the derived pointers must
// alias each other...
BasePtr1Ty = 0;
assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
"Ran out of type nesting, but not out of operands?");
return MustAlias;
}
}
// If we have seen all constant operands, and run out of indexes on one of the
// getelementptrs, check to see if the tail of the leftover one is all zeros.
// If so, return mustalias.
if (UnequalOper == MinOperands) {
if (GEP1Ops.size() < GEP2Ops.size()) std::swap(GEP1Ops, GEP2Ops);
bool AllAreZeros = true;
for (unsigned i = UnequalOper; i != MaxOperands; ++i)
if (!isa<Constant>(GEP1Ops[i]) ||
!cast<Constant>(GEP1Ops[i])->isNullValue()) {
AllAreZeros = false;
break;
}
if (AllAreZeros) return MustAlias;
}
// So now we know that the indexes derived from the base pointers,
// which are known to alias, are different. We can still determine a
// no-alias result if there are differing constant pairs in the index
// chain. For example:
// A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
//
// We have to be careful here about array accesses. In particular, consider:
// A[1][0] vs A[0][i]
// In this case, we don't *know* that the array will be accessed in bounds:
// the index could even be negative. Because of this, we have to
// conservatively *give up* and return may alias. We disregard differing
// array subscripts that are followed by a variable index without going
// through a struct.
//
unsigned SizeMax = std::max(G1S, G2S);
if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
// Scan for the first operand that is constant and unequal in the
// two getelementptrs...
unsigned FirstConstantOper = UnequalOper;
for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
const Value *G1Oper = GEP1Ops[FirstConstantOper];
const Value *G2Oper = GEP2Ops[FirstConstantOper];
if (G1Oper != G2Oper) // Found non-equal constant indexes...
if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
if (G1OC->getType() != G2OC->getType()) {
// Sign extend both operands to long.
G1OC = ConstantExpr::getSignExtend(G1OC, Type::LongTy);
G2OC = ConstantExpr::getSignExtend(G2OC, Type::LongTy);
GEP1Ops[FirstConstantOper] = G1OC;
GEP2Ops[FirstConstantOper] = G2OC;
}
if (G1OC != G2OC) {
// Handle the "be careful" case above: if this is an array
// subscript, scan for a subsequent variable array index.
if (isa<ArrayType>(BasePtr1Ty)) {
const Type *NextTy =cast<ArrayType>(BasePtr1Ty)->getElementType();
bool isBadCase = false;
for (unsigned Idx = FirstConstantOper+1;
Idx != MinOperands && isa<ArrayType>(NextTy); ++Idx) {
const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
isBadCase = true;
break;
}
NextTy = cast<ArrayType>(NextTy)->getElementType();
}
if (isBadCase) G1OC = 0;
}
// Make sure they are comparable (ie, not constant expressions), and
// make sure the GEP with the smaller leading constant is GEP1.
if (G1OC) {
Constant *Compare = ConstantExpr::getSetGT(G1OC, G2OC);
if (ConstantBool *CV = dyn_cast<ConstantBool>(Compare)) {
if (CV->getValue()) // If they are comparable and G2 > G1
std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
break;
}
}
}
}
BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
}
// No shared constant operands, and we ran out of common operands. At this
// point, the GEP instructions have run through all of their operands, and we
// haven't found evidence that there are any deltas between the GEP's.
// However, one GEP may have more operands than the other. If this is the
// case, there may still be hope. Check this now.
if (FirstConstantOper == MinOperands) {
// Make GEP1Ops be the longer one if there is a longer one.
if (GEP1Ops.size() < GEP2Ops.size())
std::swap(GEP1Ops, GEP2Ops);
// Is there anything to check?
if (GEP1Ops.size() > MinOperands) {
for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
if (isa<ConstantInt>(GEP1Ops[i]) &&
!cast<Constant>(GEP1Ops[i])->isNullValue()) {
// Yup, there's a constant in the tail. Set all variables to
// constants in the GEP instruction to make it suiteable for
// TargetData::getIndexedOffset.
for (i = 0; i != MaxOperands; ++i)
if (!isa<ConstantInt>(GEP1Ops[i]))
GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
// Okay, now get the offset. This is the relative offset for the full
// instruction.
const TargetData &TD = getTargetData();
int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
// Now crop off any constants from the end...
GEP1Ops.resize(MinOperands);
int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
// If the tail provided a bit enough offset, return noalias!
if ((uint64_t)(Offset2-Offset1) >= SizeMax)
return NoAlias;
}
}
// Couldn't find anything useful.
return MayAlias;
}
// If there are non-equal constants arguments, then we can figure
// out a minimum known delta between the two index expressions... at
// this point we know that the first constant index of GEP1 is less
// than the first constant index of GEP2.
// Advance BasePtr[12]Ty over this first differing constant operand.
BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
getTypeAtIndex(GEP2Ops[FirstConstantOper]);
BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
getTypeAtIndex(GEP1Ops[FirstConstantOper]);
// We are going to be using TargetData::getIndexedOffset to determine the
// offset that each of the GEP's is reaching. To do this, we have to convert
// all variable references to constant references. To do this, we convert the
// initial sequence of array subscripts into constant zeros to start with.
const Type *ZeroIdxTy = GEPPointerTy;
for (unsigned i = 0; i != FirstConstantOper; ++i) {
if (!isa<StructType>(ZeroIdxTy))
GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::UIntTy);
if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
}
// We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
// Loop over the rest of the operands...
for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
const Value *Op1 = i < GEP1Ops.size() ? GEP1Ops[i] : 0;
const Value *Op2 = i < GEP2Ops.size() ? GEP2Ops[i] : 0;
// If they are equal, use a zero index...
if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
if (!isa<ConstantInt>(Op1))
GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
// Otherwise, just keep the constants we have.
} else {
if (Op1) {
if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
// If this is an array index, make sure the array element is in range.
if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
if (Op1C->getRawValue() >= AT->getNumElements())
return MayAlias; // Be conservative with out-of-range accesses
} else {
// GEP1 is known to produce a value less than GEP2. To be
// conservatively correct, we must assume the largest possible
// constant is used in this position. This cannot be the initial
// index to the GEP instructions (because we know we have at least one
// element before this one with the different constant arguments), so
// we know that the current index must be into either a struct or
// array. Because we know it's not constant, this cannot be a
// structure index. Because of this, we can calculate the maximum
// value possible.
//
if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
GEP1Ops[i] = ConstantSInt::get(Type::LongTy,AT->getNumElements()-1);
}
}
if (Op2) {
if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
// If this is an array index, make sure the array element is in range.
if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
if (Op2C->getRawValue() >= AT->getNumElements())
return MayAlias; // Be conservative with out-of-range accesses
} else { // Conservatively assume the minimum value for this index
GEP2Ops[i] = Constant::getNullValue(Op2->getType());
}
}
}
if (BasePtr1Ty && Op1) {
if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
else
BasePtr1Ty = 0;
}
if (BasePtr2Ty && Op2) {
if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
else
BasePtr2Ty = 0;
}
}
if (GEPPointerTy->getElementType()->isSized()) {
int64_t Offset1 = getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops);
int64_t Offset2 = getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops);
assert(Offset1<Offset2 && "There is at least one different constant here!");
if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
//std::cerr << "Determined that these two GEP's don't alias ["
// << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
return NoAlias;
}
}
return MayAlias;
}
namespace {
struct StringCompare {
bool operator()(const char *LHS, const char *RHS) {
return strcmp(LHS, RHS) < 0;
}
};
}
// Note that this list cannot contain libm functions (such as acos and sqrt)
// that set errno on a domain or other error.
static const char *DoesntAccessMemoryFns[] = {
"abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl",
"trunc", "truncf", "truncl", "ldexp",
"atan", "atanf", "atanl", "atan2", "atan2f", "atan2l",
"cbrt",
"cos", "cosf", "cosl",
"exp", "expf", "expl",
"hypot",
"sin", "sinf", "sinl",
"tan", "tanf", "tanl", "tanh", "tanhf", "tanhl",
"floor", "floorf", "floorl", "ceil", "ceilf", "ceill",
// ctype.h
"isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint"
"ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper",
// wctype.h"
"iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower",
"iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
"iswctype", "towctrans", "towlower", "towupper",
"btowc", "wctob",
"isinf", "isnan", "finite",
// C99 math functions
"copysign", "copysignf", "copysignd",
"nexttoward", "nexttowardf", "nexttowardd",
"nextafter", "nextafterf", "nextafterd",
// ISO C99:
"__signbit", "__signbitf", "__signbitl",
};
static const char *OnlyReadsMemoryFns[] = {
"atoi", "atol", "atof", "atoll", "atoq", "a64l",
"bcmp", "memcmp", "memchr", "memrchr", "wmemcmp", "wmemchr",
// Strings
"strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp",
"strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr",
"index", "rindex",
// Wide char strings
"wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk",
"wcsrchr", "wcsspn", "wcsstr",
// glibc
"alphasort", "alphasort64", "versionsort", "versionsort64",
// C99
"nan", "nanf", "nand",
// File I/O
"feof", "ferror", "fileno",
"feof_unlocked", "ferror_unlocked", "fileno_unlocked"
};
AliasAnalysis::ModRefBehavior
BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
std::vector<PointerAccessInfo> *Info) {
if (!F->isExternal()) return UnknownModRefBehavior;
static std::vector<const char*> NoMemoryTable, OnlyReadsMemoryTable;
static bool Initialized = false;
if (!Initialized) {
NoMemoryTable.insert(NoMemoryTable.end(),
DoesntAccessMemoryFns,
DoesntAccessMemoryFns+
sizeof(DoesntAccessMemoryFns)/sizeof(DoesntAccessMemoryFns[0]));
OnlyReadsMemoryTable.insert(OnlyReadsMemoryTable.end(),
OnlyReadsMemoryFns,
OnlyReadsMemoryFns+
sizeof(OnlyReadsMemoryFns)/sizeof(OnlyReadsMemoryFns[0]));
#define GET_MODREF_BEHAVIOR
#include "llvm/Intrinsics.gen"
#undef GET_MODREF_BEHAVIOR
// Sort the table the first time through.
std::sort(NoMemoryTable.begin(), NoMemoryTable.end(), StringCompare());
std::sort(OnlyReadsMemoryTable.begin(), OnlyReadsMemoryTable.end(),
StringCompare());
Initialized = true;
}
std::vector<const char*>::iterator Ptr =
std::lower_bound(NoMemoryTable.begin(), NoMemoryTable.end(),
F->getName().c_str(), StringCompare());
if (Ptr != NoMemoryTable.end() && *Ptr == F->getName())
return DoesNotAccessMemory;
Ptr = std::lower_bound(OnlyReadsMemoryTable.begin(),
OnlyReadsMemoryTable.end(),
F->getName().c_str(), StringCompare());
if (Ptr != OnlyReadsMemoryTable.end() && *Ptr == F->getName())
return OnlyReadsMemory;
return UnknownModRefBehavior;
}
// Make sure that anything that uses AliasAnalysis pulls in this file...
DEFINING_FILE_FOR(BasicAliasAnalysis)
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