//===- 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.
//
//
//===----------------------------------------------------------------------===//
-#include "llvm/Analysis/BasicAliasAnalysis.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Pass.h"
#include "llvm/BasicBlock.h"
-#include "llvm/Support/InstVisitor.h"
-#include "llvm/iMemory.h"
-#include "llvm/iOther.h"
-#include "llvm/Constants.h"
-#include "llvm/GlobalValue.h"
-#include "llvm/DerivedTypes.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> X("Alias Analysis");
+static RegisterAnalysisGroup<AliasAnalysis> Z("Alias Analysis");
+char AliasAnalysis::ID = 0;
-// CanModify - Define a little visitor class that is used to check to see if
-// arbitrary chunks of code can modify a specified pointer.
-//
-namespace {
- struct CanModify : public InstVisitor<CanModify, bool> {
- const AliasAnalysis &AA;
- const Value *Ptr;
+//===----------------------------------------------------------------------===//
+// Default chaining methods
+//===----------------------------------------------------------------------===//
- CanModify(const AliasAnalysis *aa, const Value *ptr)
- : AA(*aa), Ptr(ptr) {}
+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 visitInvokeInst(InvokeInst &II) {
- return AA.canInvokeModify(II, Ptr);
- }
- bool visitCallInst(CallInst &CI) {
- return AA.canCallModify(CI, Ptr);
- }
- bool visitStoreInst(StoreInst &SI) {
- return AA.alias(Ptr, SI.getOperand(1));
+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(ImmutableCallSite CS,
+ const Value *P, unsigned Size) {
+ // Don't assert AA because BasicAA calls us in order to make use of the
+ // logic here.
+
+ 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 (ImmutableCallSite::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 P points to a constant memory location, the call definitely could not
+ // modify the memory location.
+ if ((Mask & Mod) && pointsToConstantMemory(P))
+ Mask = ModRefResult(Mask & ~Mod);
+
+ // If this is BasicAA, don't forward.
+ if (!AA) return Mask;
+
+ // Otherwise, fall back to the next AA in the chain. But we can merge
+ // in any mask we've managed to compute.
+ return ModRefResult(AA->getModRefInfo(CS, P, Size) & Mask);
+}
+
+AliasAnalysis::ModRefResult
+AliasAnalysis::getModRefInfo(ImmutableCallSite CS1, ImmutableCallSite CS2) {
+ // Don't assert AA because BasicAA calls us in order to make use of the
+ // logic here.
+
+ // If CS1 or CS2 are readnone, they don't interact.
+ ModRefBehavior CS1B = getModRefBehavior(CS1);
+ if (CS1B == DoesNotAccessMemory) return NoModRef;
+
+ ModRefBehavior CS2B = getModRefBehavior(CS2);
+ if (CS2B == DoesNotAccessMemory) return NoModRef;
+
+ // If they both only read from memory, there is no dependence.
+ if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory)
+ return NoModRef;
+
+ AliasAnalysis::ModRefResult Mask = ModRef;
+
+ // If CS1 only reads memory, the only dependence on CS2 can be
+ // from CS1 reading memory written by CS2.
+ if (CS1B == OnlyReadsMemory)
+ Mask = ModRefResult(Mask & Ref);
+
+ // If CS2 only access memory through arguments, accumulate the mod/ref
+ // information from CS1's references to the memory referenced by
+ // CS2's arguments.
+ if (CS2B == AccessesArguments) {
+ AliasAnalysis::ModRefResult R = NoModRef;
+ for (ImmutableCallSite::arg_iterator
+ I = CS2.arg_begin(), E = CS2.arg_end(); I != E; ++I) {
+ R = ModRefResult((R | getModRefInfo(CS1, *I, UnknownSize)) & Mask);
+ if (R == Mask)
+ break;
}
+ return R;
+ }
+
+ // If CS1 only accesses memory through arguments, check if CS2 references
+ // any of the memory referenced by CS1's arguments. If not, return NoModRef.
+ if (CS1B == AccessesArguments) {
+ AliasAnalysis::ModRefResult R = NoModRef;
+ for (ImmutableCallSite::arg_iterator
+ I = CS1.arg_begin(), E = CS1.arg_end(); I != E; ++I)
+ if (getModRefInfo(CS2, *I, UnknownSize) != NoModRef) {
+ R = Mask;
+ break;
+ }
+ if (R == NoModRef)
+ return R;
+ }
+
+ // If this is BasicAA, don't forward.
+ if (!AA) return Mask;
- // Other instructions do not alias anything.
- bool visitInstruction(Instruction &I) { return false; }
- };
+ // Otherwise, fall back to the next AA in the chain. But we can merge
+ // in any mask we've managed to compute.
+ return ModRefResult(AA->getModRefInfo(CS1, CS2) & Mask);
+}
+
+AliasAnalysis::ModRefBehavior
+AliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
+ // Don't assert AA because BasicAA calls us in order to make use of the
+ // logic here.
+
+ ModRefBehavior Min = UnknownModRefBehavior;
+
+ // Call back into the alias analysis with the other form of getModRefBehavior
+ // to see if it can give a better response.
+ if (const Function *F = CS.getCalledFunction())
+ Min = getModRefBehavior(F);
+
+ // If this is BasicAA, don't forward.
+ if (!AA) return Min;
+
+ // Otherwise, fall back to the next AA in the chain. But we can merge
+ // in any result we've managed to compute.
+ return std::min(AA->getModRefBehavior(CS), Min);
+}
+
+AliasAnalysis::ModRefBehavior
+AliasAnalysis::getModRefBehavior(const Function *F) {
+ assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
+ return AA->getModRefBehavior(F);
+}
+
+
+//===----------------------------------------------------------------------===//
+// AliasAnalysis non-virtual helper method implementation
+//===----------------------------------------------------------------------===//
+
+AliasAnalysis::ModRefResult
+AliasAnalysis::getModRefInfo(const LoadInst *L, const Value *P, unsigned Size) {
+ // Be conservative in the face of volatile.
+ if (L->isVolatile())
+ return ModRef;
+
+ // If the load address doesn't alias the given address, it doesn't read
+ // or write the specified memory.
+ if (!alias(L->getOperand(0), getTypeStoreSize(L->getType()), P, Size))
+ return NoModRef;
+
+ // Otherwise, a load just reads.
+ return Ref;
+}
+
+AliasAnalysis::ModRefResult
+AliasAnalysis::getModRefInfo(const StoreInst *S, const Value *P, unsigned Size) {
+ // Be conservative in the face of volatile.
+ if (S->isVolatile())
+ return ModRef;
+
+ // If the store address cannot alias the pointer in question, then the
+ // specified memory 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.
+ if (pointsToConstantMemory(P))
+ return NoModRef;
+
+ // Otherwise, a store just writes.
+ return Mod;
+}
+
+AliasAnalysis::ModRefResult
+AliasAnalysis::getModRefInfo(const VAArgInst *V, const Value *P, unsigned Size) {
+ // If the va_arg address cannot alias the pointer in question, then the
+ // specified memory cannot be accessed by the va_arg.
+ if (!alias(V->getOperand(0), UnknownSize, P, Size))
+ return NoModRef;
+
+ // If the pointer is a pointer to constant memory, then it could not have been
+ // modified by this va_arg.
+ if (pointsToConstantMemory(P))
+ return NoModRef;
+
+ // Otherwise, a va_arg reads and writes.
+ return ModRef;
+}
+
+
+AliasAnalysis::ModRefBehavior
+AliasAnalysis::getIntrinsicModRefBehavior(unsigned iid) {
+#define GET_INTRINSIC_MODREF_BEHAVIOR
+#include "llvm/Intrinsics.gen"
+#undef GET_INTRINSIC_MODREF_BEHAVIOR
}
// AliasAnalysis destructor: DO NOT move this to the header file for
//
AliasAnalysis::~AliasAnalysis() {}
-/// canBasicBlockModify - Return true if it is possible for execution of the
-/// specified basic block to modify the value pointed to by Ptr.
+/// InitializeAliasAnalysis - Subclasses must call this method to initialize the
+/// AliasAnalysis interface before any other methods are called.
///
-bool AliasAnalysis::canBasicBlockModify(const BasicBlock &bb,
- const Value *Ptr) const {
- CanModify CM(this, Ptr);
- BasicBlock &BB = const_cast<BasicBlock&>(bb);
+void AliasAnalysis::InitializeAliasAnalysis(Pass *P) {
+ TD = P->getAnalysisIfAvailable<TargetData>();
+ AA = &P->getAnalysis<AliasAnalysis>();
+}
- for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I)
- if (CM.visit(I)) // Check every instruction in the basic block...
- return true;
+// 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
+}
- return false;
+/// 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
///
bool AliasAnalysis::canInstructionRangeModify(const Instruction &I1,
const Instruction &I2,
- const Value *Ptr) const {
+ const Value *Ptr, unsigned Size) {
assert(I1.getParent() == I2.getParent() &&
"Instructions not in same basic block!");
- CanModify CM(this, Ptr);
- BasicBlock::iterator I = const_cast<Instruction*>(&I1);
- BasicBlock::iterator E = const_cast<Instruction*>(&I2);
+ BasicBlock::const_iterator I = &I1;
+ BasicBlock::const_iterator E = &I2;
++E; // Convert from inclusive to exclusive range.
- for (; I != E; ++I)
- if (CM.visit(I)) // Check every instruction in the basic block...
+ for (; I != E; ++I) // Check every instruction in range
+ if (getModRefInfo(I, Ptr, Size) & Mod)
return true;
-
return false;
}
-//===----------------------------------------------------------------------===//
-// BasicAliasAnalysis Pass Implementation
-//===----------------------------------------------------------------------===//
-//
-// Because of the way .a files work, the implementation of the
-// BasicAliasAnalysis class MUST be in the AliasAnalysis file itself, or else we
-// run the risk of AliasAnalysis being used, but the default implementation not
-// being linked into the tool that uses it. As such, we register and implement
-// the class here.
-//
-namespace {
- // 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
-
-
-
-// hasUniqueAddress - Return true if the
-static inline bool hasUniqueAddress(const Value *V) {
- return isa<GlobalValue>(V) || isa<MallocInst>(V) || isa<AllocaInst>(V);
+/// 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 ImmutableCallSite(cast<Instruction>(V))
+ .paramHasAttr(0, Attribute::NoAlias);
+ return false;
}
-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)) 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));
- }
- return 0;
+/// 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))
+ return true;
+ if (isa<GlobalValue>(V) && !isa<GlobalAlias>(V))
+ return true;
+ if (isNoAliasCall(V))
+ return true;
+ if (const Argument *A = dyn_cast<Argument>(V))
+ return A->hasNoAliasAttr() || A->hasByValAttr();
+ return false;
}
-// 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::Result BasicAliasAnalysis::alias(const Value *V1,
- const Value *V2) const {
- // 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;
- }
-
- // 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 discernable object?
- if (O1 && O2) {
- // If they are two different objects, we know that we have no alias...
- if (O1 != O2) 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.
- } else if (O1 && isa<ConstantPointerNull>(V2)) {
- return NoAlias; // Unique values don't alias null
- } else if (O2 && isa<ConstantPointerNull>(V1)) {
- return NoAlias; // Unique values don't alias null
- }
-
- return MayAlias;
-}
+// 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)
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