-AliasAnalysis::Result BasicAliasAnalysis::alias(const Value *V1,
- const Value *V2) {
- // Strip off constant pointer refs if they exist
- if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V1))
- V1 = CPR->getValue();
- if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V2))
- V2 = CPR->getValue();
-
- // 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))
- return alias(I->getOperand(0), V2);
- if (const Instruction *I = dyn_cast<CastInst>(V2))
- return alias(I->getOperand(0), V1);
-
- // If we have two gep instructions with identical indices, return an alias
- // result equal to the alias result of the original pointer...
- //
- if (const GetElementPtrInst *GEP1 = dyn_cast<GetElementPtrInst>(V1))
- if (const GetElementPtrInst *GEP2 = dyn_cast<GetElementPtrInst>(V2))
- if (GEP1->getNumOperands() == GEP2->getNumOperands() &&
- GEP1->getOperand(0)->getType() == GEP2->getOperand(0)->getType()) {
- if (std::equal(GEP1->op_begin()+1, GEP1->op_end(), GEP2->op_begin()+1))
- return alias(GEP1->getOperand(0), GEP2->getOperand(0));
-
- // If all of the indexes to the getelementptr are constant, but
- // different (well we already know they are different), then we know
- // that there cannot be an alias here if the two base pointers DO alias.
- //
- bool AllConstant = true;
- for (unsigned i = 1, e = GEP1->getNumOperands(); i != e; ++i)
- if (!isa<Constant>(GEP1->getOperand(i)) ||
- !isa<Constant>(GEP2->getOperand(i))) {
- AllConstant = false;
- break;
- }
-
- // If we are all constant, then look at where the the base pointers
- // alias. If they are known not to alias, then we are dealing with two
- // different arrays or something, so no alias is possible. If they are
- // known to be the same object, then we cannot alias because we are
- // indexing into a different part of the object. As usual, MayAlias
- // doesn't tell us anything.
- //
- if (AllConstant &&
- alias(GEP1->getOperand(0), GEP2->getOperand(1)) != MayAlias)
- return ::NoAlias();
- }