#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
-#include "llvm/ParameterAttributes.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include <algorithm>
using namespace llvm;
+//===----------------------------------------------------------------------===//
+// Useful predicates
+//===----------------------------------------------------------------------===//
+
+// Determine if an AllocationInst instruction escapes from the function it is
+// contained in. If it does not escape, there is no way for another function to
+// mod/ref it. We do this by looking at its uses and determining if the uses
+// can escape (recursively).
+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; //next use.
+ case Instruction::Store:
+ if (I->getOperand(0) == V)
+ return true; // Escapes if the pointer is stored.
+ break; // next use.
+ case Instruction::GetElementPtr:
+ if (AddressMightEscape(I))
+ return true;
+ break; // next use.
+ case Instruction::BitCast:
+ if (AddressMightEscape(I))
+ return true;
+ break; // next use
+ case Instruction::Ret:
+ // If returned, the address will escape to calling functions, but no
+ // callees could modify it.
+ break; // next use
+ case Instruction::Call:
+ // If the call is to a few known safe intrinsics, we know that it does
+ // not escape.
+ // TODO: Eventually just check the 'nocapture' attribute.
+ if (!isa<MemIntrinsic>(I))
+ return true;
+ break; // next use
+ default:
+ return true;
+ }
+ }
+ return false;
+}
+
+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,
+ SmallVector<Value*, 16> &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;
+}
+
+/// isNoAliasCall - Return true if this pointer is returned by a noalias
+/// function.
+static bool 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
+/// Allocas and Mallocs
+/// ByVal and NoAlias Arguments
+/// NoAlias returns
+///
+static bool isIdentifiedObject(const Value *V) {
+ if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isNoAliasCall(V))
+ return true;
+ if (const Argument *A = dyn_cast<Argument>(V))
+ return A->hasNoAliasAttr() || A->hasByValAttr();
+ return false;
+}
+
+/// isKnownNonNull - Return true if we know that the specified value is never
+/// null.
+static bool isKnownNonNull(const Value *V) {
+ // Alloca never returns null, malloc might.
+ if (isa<AllocaInst>(V)) return true;
+
+ // A byval argument is never null.
+ if (const Argument *A = dyn_cast<Argument>(V))
+ return A->hasByValAttr();
+
+ // Global values are not null unless extern weak.
+ if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
+ return !GV->hasExternalWeakLinkage();
+ return false;
+}
+
+/// isNonEscapingLocalObject - Return true if the pointer is to a function-local
+/// object that never escapes from the function.
+static bool isNonEscapingLocalObject(const Value *V) {
+ // If this is a local allocation, check to see if it escapes.
+ if (isa<AllocationInst>(V) || isNoAliasCall(V))
+ return !AddressMightEscape(V);
+
+ // If this is an argument that corresponds to a byval or noalias argument,
+ // it can't escape either.
+ if (const Argument *A = dyn_cast<Argument>(V))
+ if (A->hasByValAttr() || A->hasNoAliasAttr())
+ return !AddressMightEscape(V);
+ return false;
+}
+
+
+/// isObjectSmallerThan - Return true if we can prove that the object specified
+/// by V is smaller than Size.
+static bool isObjectSmallerThan(const Value *V, unsigned Size,
+ const TargetData &TD) {
+ const Type *AccessTy = 0;
+ if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
+ AccessTy = GV->getType()->getElementType();
+
+ if (const AllocationInst *AI = dyn_cast<AllocationInst>(V))
+ if (!AI->isArrayAllocation())
+ AccessTy = AI->getType()->getElementType();
+
+ if (const Argument *A = dyn_cast<Argument>(V))
+ if (A->hasByValAttr())
+ AccessTy = cast<PointerType>(A->getType())->getElementType();
+
+ if (AccessTy && AccessTy->isSized())
+ return TD.getABITypeSize(AccessTy) < Size;
+ return false;
+}
+
+//===----------------------------------------------------------------------===//
+// NoAA Pass
+//===----------------------------------------------------------------------===//
+
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
///
struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
static char ID; // Class identification, replacement for typeinfo
- NoAA() : ImmutablePass((intptr_t)&ID) {}
- explicit NoAA(intptr_t PID) : ImmutablePass(PID) { }
+ NoAA() : ImmutablePass(&ID) {}
+ explicit NoAA(void *PID) : ImmutablePass(PID) { }
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<TargetData>();
virtual void deleteValue(Value *V) {}
virtual void copyValue(Value *From, Value *To) {}
};
+} // End of anonymous namespace
- // Register this pass...
- char NoAA::ID = 0;
- RegisterPass<NoAA>
- U("no-aa", "No Alias Analysis (always returns 'may' alias)");
+// Register this pass...
+char NoAA::ID = 0;
+static RegisterPass<NoAA>
+U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true);
- // Declare that we implement the AliasAnalysis interface
- RegisterAnalysisGroup<AliasAnalysis> V(U);
-} // End of anonymous namespace
+// Declare that we implement the AliasAnalysis interface
+static RegisterAnalysisGroup<AliasAnalysis> V(U);
ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
+//===----------------------------------------------------------------------===//
+// BasicAA Pass
+//===----------------------------------------------------------------------===//
+
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 VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
static char ID; // Class identification, replacement for typeinfo
- BasicAliasAnalysis() : NoAA((intptr_t)&ID) { }
+ BasicAliasAnalysis() : NoAA(&ID) {}
AliasResult alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size);
const Type *BasePtr2Ty,
Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
};
+} // End of anonymous namespace
- // Register this pass...
- char BasicAliasAnalysis::ID = 0;
- RegisterPass<BasicAliasAnalysis>
- X("basicaa", "Basic Alias Analysis (default AA impl)");
+// Register this pass...
+char BasicAliasAnalysis::ID = 0;
+static RegisterPass<BasicAliasAnalysis>
+X("basicaa", "Basic Alias Analysis (default AA impl)", false, true);
- // Declare that we implement the AliasAnalysis interface
- RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
-} // End of anonymous namespace
+// Declare that we implement the AliasAnalysis interface
+static RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
ImmutablePass *llvm::createBasicAliasAnalysisPass() {
return new BasicAliasAnalysis();
}
-/// 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. This returns:
-/// Arguments, GlobalVariables, Functions, Allocas, Mallocs.
-static const Value *getUnderlyingObject(const Value *V) {
- if (!isa<PointerType>(V->getType())) return 0;
-
- // If we are at some type of object, return it. GlobalValues and Allocations
- // have unique addresses.
- if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isa<Argument>(V))
- return V;
-
- // Traverse through different addressing mechanisms...
- if (const Instruction *I = dyn_cast<Instruction>(V)) {
- if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I))
- return getUnderlyingObject(I->getOperand(0));
- } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
- if (CE->getOpcode() == Instruction::BitCast ||
- CE->getOpcode() == Instruction::GetElementPtr)
- return getUnderlyingObject(CE->getOperand(0));
- }
- 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,
- SmallVector<Value*, 16> &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;
-}
-
-// Determine if an AllocationInst instruction escapes from the function it is
-// contained in. If it does not escape, there is no way for another function to
-// mod/ref it. We do this by looking at its uses and determining if the uses
-// can escape (recursively).
-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; //next use.
- case Instruction::Store:
- if (I->getOperand(0) == V)
- return true; // Escapes if the pointer is stored.
- break; // next use.
- case Instruction::GetElementPtr:
- if (AddressMightEscape(I))
- return true;
- break; // next use.
- case Instruction::BitCast:
- if (AddressMightEscape(I))
- return true;
- break; // next use
- case Instruction::Ret:
- // If returned, the address will escape to calling functions, but no
- // callees could modify it.
- break; // next use
- case Instruction::Call:
- // If the call is to a few known safe intrinsics, we know that it does
- // not escape
- if (!isa<MemIntrinsic>(I))
- return true;
- break; // next use
- default:
- return true;
- }
- }
+ if (const GlobalVariable *GV =
+ dyn_cast<GlobalVariable>(P->getUnderlyingObject()))
+ return GV->isConstant();
return false;
}
AliasAnalysis::ModRefResult
BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
if (!isa<Constant>(P)) {
- const Value *Object = getUnderlyingObject(P);
- // Allocations and byval arguments are "new" objects.
- if (Object &&
- (isa<AllocationInst>(Object) || isa<Argument>(Object))) {
- // Okay, the pointer is to a stack allocated (or effectively so, for
- // for noalias parameters) object. If the address of this object doesn't
- // escape from this function body to a callee, then we know that no
- // callees can mod/ref it unless they are actually passed it.
- if (isa<AllocationInst>(Object) ||
- cast<Argument>(Object)->hasByValAttr() ||
- cast<Argument>(Object)->hasNoAliasAttr())
- if (!AddressMightEscape(Object)) {
- bool passedAsArg = false;
- for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
- CI != CE; ++CI)
- if (isa<PointerType>((*CI)->getType()) &&
- getUnderlyingObject(*CI) == P)
- passedAsArg = true;
-
- if (!passedAsArg)
- 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 (isa<AllocaInst>(Object) ||
- (isa<Argument>(Object) && cast<Argument>(Object)->hasByValAttr()))
- if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
- if (CI->isTailCall())
- return NoModRef;
+ const Value *Object = P->getUnderlyingObject();
+
+ // 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.
+ // We cannot exclude byval arguments here; these belong to the caller of
+ // the current function not to the current function, and a tail callee
+ // may reference them.
+ if (isa<AllocaInst>(Object))
+ if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
+ if (CI->isTailCall())
+ return NoModRef;
+
+ // If the pointer is to a locally allocated object that does not escape,
+ // then the call can not mod/ref the pointer unless the call takes the
+ // argument without capturing it.
+ if (isNonEscapingLocalObject(Object)) {
+ bool passedAsArg = false;
+ // TODO: Eventually only check 'nocapture' arguments.
+ for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
+ CI != CE; ++CI)
+ if (isa<PointerType>((*CI)->getType()) &&
+ alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias)
+ passedAsArg = true;
+
+ if (!passedAsArg)
+ return NoModRef;
}
}
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. :)
// 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::Int64Ty && V2->getType() != Type::Int64Ty)
+ if (!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType()))
return NoAlias; // Scalars cannot alias each other
// Strip off cast instructions...
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 (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
- // Incoming argument cannot alias locally allocated object!
- if (isa<AllocationInst>(O2)) return NoAlias;
-
- // If they are two different objects, and one is a noalias argument
- // then they do not alias.
- if (O1 != O2 && O1Arg->hasNoAliasAttr())
- return NoAlias;
-
- // Byval arguments can't alias globals or other arguments.
- if (O1 != O2 && O1Arg->hasByValAttr()) return NoAlias;
-
- // Otherwise, nothing is known...
- }
-
- if (const Argument *O2Arg = dyn_cast<Argument>(O2)) {
- // Incoming argument cannot alias locally allocated object!
- if (isa<AllocationInst>(O1)) return NoAlias;
-
- // If they are two different objects, and one is a noalias argument
- // then they do not alias.
- if (O1 != O2 && O2Arg->hasNoAliasAttr())
- return NoAlias;
-
- // Byval arguments can't alias globals or other arguments.
- if (O1 != O2 && O2Arg->hasByValAttr()) return NoAlias;
-
- // Otherwise, nothing is known...
-
- } else if (O1 != O2 && !isa<Argument>(O1)) {
- // If they are two different objects, and neither is an argument,
- // 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.
- }
+ const Value *O1 = V1->getUnderlyingObject();
+ const Value *O2 = V2->getUnderlyingObject();
- // Unique values don't alias null, except non-byval arguments.
- if (isa<ConstantPointerNull>(V2)) {
- if (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
- if (O1Arg->hasByValAttr())
- return NoAlias;
- } else {
- return NoAlias;
- }
- }
-
- 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().getABITypeSize(ElTy);
- if (GlobalSize < V2Size && V2Size != ~0U)
- return NoAlias;
- }
- }
+ if (O1 != O2) {
+ // If V1/V2 point to two different objects we know that we have no alias.
+ if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
+ return NoAlias;
+
+ // Arguments can't alias with local allocations or noalias calls.
+ if ((isa<Argument>(O1) && (isa<AllocationInst>(O2) || isNoAliasCall(O2))) ||
+ (isa<Argument>(O2) && (isa<AllocationInst>(O1) || isNoAliasCall(O1))))
+ 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().getABITypeSize(ElTy);
- if (GlobalSize < V1Size && V1Size != ~0U)
- return NoAlias;
- }
+ // Most objects can't alias null.
+ if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) ||
+ (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2)))
+ return NoAlias;
}
-
+
+ // If the size of one access is larger than the entire object on the other
+ // side, then we know such behavior is undefined and can assume no alias.
+ const TargetData &TD = getTargetData();
+ if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, TD)) ||
+ (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, TD)))
+ return NoAlias;
+
+ // If one pointer is the result of a call/invoke and the other is a
+ // non-escaping local object, then we know the object couldn't escape to a
+ // point where the call could return it.
+ if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
+ isNonEscapingLocalObject(O2))
+ return NoAlias;
+ if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
+ isNonEscapingLocalObject(O1))
+ 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
if (isa<ConstantInt>(GEP1Ops[i]) &&
!cast<ConstantInt>(GEP1Ops[i])->isZero()) {
// Yup, there's a constant in the tail. Set all variables to
- // constants in the GEP instruction to make it suiteable for
+ // constants in the GEP instruction to make it suitable for
// TargetData::getIndexedOffset.
for (i = 0; i != MaxOperands; ++i)
if (!isa<ConstantInt>(GEP1Ops[i]))
int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
MinOperands);
+ // Make sure we compare the absolute difference.
+ if (Offset1 > Offset2)
+ std::swap(Offset1, Offset2);
+
// If the tail provided a bit enough offset, return noalias!
if ((uint64_t)(Offset2-Offset1) >= SizeMax)
return NoAlias;
+ // Otherwise break - we don't look for another constant in the tail.
+ break;
}
}
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