-//===- llvm/Analysis/BasicAliasAnalysis.h - Alias Analysis Impl -*- C++ -*-===//
+//===- 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,
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/AliasAnalysis.h"
-#include "llvm/Pass.h"
-#include "llvm/iMemory.h"
-#include "llvm/iOther.h"
-#include "llvm/ConstantHandling.h"
-#include "llvm/GlobalValue.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"
-
-// Make sure that anything that uses AliasAnalysis pulls in this file...
-void BasicAAStub() {}
-
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/GetElementPtrTypeIterator.h"
+#include "llvm/Support/ManagedStatic.h"
+#include <algorithm>
+using namespace llvm;
namespace {
- struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis {
-
+ /// 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 VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AliasAnalysis::getAnalysisUsage(AU);
+ AU.addRequired<TargetData>();
}
-
- virtual void initializePass();
- // alias - This is the only method here that does anything interesting...
- //
+ 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...
+ RegisterPass<NoAA>
+ U("no-aa", "No Alias Analysis (always returns 'may' alias)");
+
+ // Declare that we implement the AliasAnalysis interface
+ RegisterAnalysisGroup<AliasAnalysis> V(U);
+} // 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 VISIBILITY_HIDDEN 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 of compatible types and
- // equal number of arguments. This checks to see if the index expressions
+ // 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(GetElementPtrInst *GEP1, unsigned G1Size,
- GetElementPtrInst *GEP2, unsigned G2Size);
+ AliasResult
+ CheckGEPInstructions(const Type* BasePtr1Ty,
+ Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
+ const Type *BasePtr2Ty,
+ Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
};
-
+
// Register this pass...
- RegisterOpt<BasicAliasAnalysis>
+ RegisterPass<BasicAliasAnalysis>
X("basicaa", "Basic Alias Analysis (default AA impl)");
// Declare that we implement the AliasAnalysis interface
- RegisterAnalysisGroup<AliasAnalysis, BasicAliasAnalysis, true> Y;
+ RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
} // End of anonymous namespace
-void BasicAliasAnalysis::initializePass() {
- InitializeAliasAnalysis(this);
-}
-
-
-
-// hasUniqueAddress - Return true if the
-static inline bool hasUniqueAddress(const Value *V) {
- return isa<GlobalValue>(V) || isa<MallocInst>(V) || isa<AllocaInst>(V);
+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.
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;
-
+ // 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<CastInst>(I) || isa<GetElementPtrInst>(I))
+ 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::Cast ||
+ if (CE->getOpcode() == Instruction::BitCast ||
CE->getOpcode() == Instruction::GetElementPtr)
return getUnderlyingObject(CE->getOperand(0));
- } else if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V)) {
- return CPR->getValue();
}
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;
+ case Instruction::BitCast:
+ if (!isa<PointerType>(I->getType()))
+ return true;
+ 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
+ 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.
AliasAnalysis::AliasResult
BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size) {
- // 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();
+ // Strip off any constant expression casts if they exist
+ if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
+ if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
+ V1 = CE->getOperand(0);
+ if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
+ if (CE->isCast() && 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)
+ V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty)
return NoAlias; // Scalars cannot alias each other
// Strip off cast instructions...
- if (const Instruction *I = dyn_cast<CastInst>(V1))
+ if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
return alias(I->getOperand(0), V1Size, V2, V2Size);
- if (const Instruction *I = dyn_cast<CastInst>(V2))
+ if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
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 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
+ // 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 identical indices, return an alias
- // result equal to the alias result of the original pointer...
+ // 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 (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 (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, ~0U, BasePtr2, ~0U);
+ 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
+ SmallVector<Value*, 16> 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((GetElementPtrInst*)GEP1, V1Size,
- (GetElementPtrInst*)GEP2, V2Size);
+ CheckGEPInstructions(BasePtr1->getType(),
+ &GEP1Ops[0], GEP1Ops.size(), V1Size,
+ BasePtr2->getType(),
+ &GEP2Ops[0], GEP2Ops.size(), 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 (isa<GetElementPtrInst>(V2)) {
+ if (isGEP(V2)) {
std::swap(V1, V2);
std::swap(V1Size, V2Size);
}
if (V1Size != ~0U && V2Size != ~0U)
- if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V1)) {
- AliasResult R = alias(GEP->getOperand(0), V1Size, V2, V2Size);
+ if (isGEP(V1)) {
+ SmallVector<Value*, 16> 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;
- for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i)
- if (const Constant *C = dyn_cast<Constant>(GEP->getOperand(i)))
+ 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...
-
- std::vector<Value*> Indices;
- Indices.reserve(GEP->getNumOperands()-1);
- for (unsigned i = 1; i != GEP->getNumOperands(); ++i)
- if (const Constant *C = dyn_cast<Constant>(GEP->getOperand(i)))
- Indices.push_back((Value*)C);
- else
- Indices.push_back(Constant::getNullValue(Type::LongTy));
- const Type *Ty = GEP->getOperand(0)->getType();
- int Offset = getTargetData().getIndexedOffset(Ty, Indices);
- if (Offset >= (int)V2Size || Offset <= -(int)V1Size)
- return NoAlias;
+ 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[0],
+ GEPOperands.size());
+
+ if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
+ return NoAlias;
+ }
}
}
}
-
+
return MayAlias;
}
-static Value *CheckArrayIndicesForOverflow(const Type *PtrTy,
- const std::vector<Value*> &Indices,
- const ConstantInt *Idx) {
- if (const ConstantSInt *IdxS = dyn_cast<ConstantSInt>(Idx)) {
- if (IdxS->getValue() < 0) // Underflow on the array subscript?
- return Constant::getNullValue(Type::LongTy);
- else { // Check for overflow
- const ArrayType *ATy =
- cast<ArrayType>(GetElementPtrInst::getIndexedType(PtrTy, Indices,true));
- if (IdxS->getValue() >= (int64_t)ATy->getNumElements())
- return ConstantSInt::get(Type::LongTy, ATy->getNumElements()-1);
+// This function is used to determin if the indices of two GEP instructions are
+// equal. V1 and V2 are the indices.
+static bool IndexOperandsEqual(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, if necessary
+ if (C1->getType() != Type::Int64Ty)
+ C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
+ if (C2->getType() != Type::Int64Ty)
+ C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
+ return C1 == C2;
}
- }
- return (Value*)Idx; // Everything is acceptable.
+ return false;
}
-// CheckGEPInstructions - Check two GEP instructions of compatible types and
-// equal number of arguments. This checks to see if the index expressions
-// preclude the pointers from aliasing...
-//
-AliasAnalysis::AliasResult
-BasicAliasAnalysis::CheckGEPInstructions(GetElementPtrInst *GEP1, unsigned G1S,
- GetElementPtrInst *GEP2, unsigned G2S){
- // Do the base pointers alias?
- AliasResult BaseAlias = alias(GEP1->getOperand(0), G1S,
- GEP2->getOperand(0), G2S);
- if (BaseAlias != MustAlias) // No or May alias: We cannot add anything...
- return BaseAlias;
-
- // Find the (possibly empty) initial sequence of equal values...
- unsigned NumGEPOperands = GEP1->getNumOperands();
- unsigned UnequalOper = 1;
- while (UnequalOper != NumGEPOperands &&
- GEP1->getOperand(UnequalOper) == GEP2->getOperand(UnequalOper))
+/// 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, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
+ const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, 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 = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
+ unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
+ unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
+ unsigned UnequalOper = 0;
+ while (UnequalOper != MinOperands &&
+ IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
+ // Advance through the type as we go...
++UnequalOper;
-
- // If all operands equal each other, then the derived pointers must
- // alias each other...
- if (UnequalOper == NumGEPOperands) return MustAlias;
-
+ 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 (NumGEP1Ops < NumGEP2Ops) {
+ std::swap(GEP1Ops, GEP2Ops);
+ std::swap(NumGEP1Ops, NumGEP2Ops);
+ }
+
+ 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...
+ if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
// Scan for the first operand that is constant and unequal in the
- // two getelemenptrs...
+ // two getelementptrs...
unsigned FirstConstantOper = UnequalOper;
- for (; FirstConstantOper != NumGEPOperands; ++FirstConstantOper) {
- const Value *G1Oper = GEP1->getOperand(FirstConstantOper);
- const Value *G2Oper = GEP2->getOperand(FirstConstantOper);
- if (G1Oper != G2Oper && // Found non-equal constant indexes...
- isa<Constant>(G1Oper) && isa<Constant>(G2Oper)) {
- // Make sure they are comparable... and make sure the GEP with
- // the smaller leading constant is GEP1.
- ConstantBool *Compare =
- *cast<Constant>(GEP1->getOperand(FirstConstantOper)) >
- *cast<Constant>(GEP2->getOperand(FirstConstantOper));
- if (Compare) { // If they are comparable...
- if (Compare->getValue())
- std::swap(GEP1, GEP2); // Make GEP1 < GEP2
- break;
- }
+ 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.
+ if (G1OC->getType() != Type::Int64Ty)
+ G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
+ if (G2OC->getType() != Type::Int64Ty)
+ G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
+ GEP1Ops[FirstConstantOper] = G1OC;
+ GEP2Ops[FirstConstantOper] = G2OC;
+ }
+
+ if (G1OC != G2OC) {
+ // Handle the "be careful" case above: if this is an array/packed
+ // subscript, scan for a subsequent variable array index.
+ if (isa<SequentialType>(BasePtr1Ty)) {
+ const Type *NextTy =
+ cast<SequentialType>(BasePtr1Ty)->getElementType();
+ bool isBadCase = false;
+
+ for (unsigned Idx = FirstConstantOper+1;
+ Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
+ const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
+ if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
+ isBadCase = true;
+ break;
+ }
+ NextTy = cast<SequentialType>(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::getICmp(ICmpInst::ICMP_SGT,
+ G1OC, G2OC);
+ if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
+ if (CV->getZExtValue()) { // If they are comparable and G2 > G1
+ std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
+ std::swap(NumGEP1Ops, NumGEP2Ops);
+ }
+ 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 (NumGEP1Ops < NumGEP2Ops) {
+ std::swap(GEP1Ops, GEP2Ops);
+ std::swap(NumGEP1Ops, NumGEP2Ops);
+ }
+
+ // Is there anything to check?
+ if (NumGEP1Ops > 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,
+ NumGEP1Ops);
+
+ // Now check without any constants at the end.
+ int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
+ MinOperands);
+
+ // 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;
}
-
- // No constant operands, we cannot tell anything...
- if (FirstConstantOper == NumGEPOperands) 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.
- //
- std::vector<Value*> Indices1;
- Indices1.reserve(NumGEPOperands-1);
- for (unsigned i = 1; i != FirstConstantOper; ++i)
- if (GEP1->getOperand(i)->getType() == Type::UByteTy)
- Indices1.push_back(GEP1->getOperand(i));
- else
- Indices1.push_back(Constant::getNullValue(Type::LongTy));
- std::vector<Value*> Indices2;
- Indices2.reserve(NumGEPOperands-1);
- Indices2 = Indices1; // Copy the zeros prefix...
-
- // Add the two known constant operands...
- Indices1.push_back((Value*)GEP1->getOperand(FirstConstantOper));
- Indices2.push_back((Value*)GEP2->getOperand(FirstConstantOper));
-
- const Type *GEPPointerTy = GEP1->getOperand(0)->getType();
-
+
+ // 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::Int32Ty);
+
+ 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 != NumGEPOperands; ++i) {
- const Value *Op1 = GEP1->getOperand(i);
- const Value *Op2 = GEP2->getOperand(i);
- if (Op1 == Op2) { // If they are equal, use a zero index...
- Indices1.push_back(Constant::getNullValue(Op1->getType()));
- Indices2.push_back(Indices1.back());
+ for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
+ const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
+ const Value *Op2 = i < NumGEP2Ops ? 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 (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
- // If this is an array index, make sure the array element is in range...
- if (i != 1) // The pointer index can be "out of range"
- Op1 = CheckArrayIndicesForOverflow(GEPPointerTy, Indices1, Op1C);
-
- Indices1.push_back((Value*)Op1);
- } 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.
- //
- const ArrayType *ElTy =
- cast<ArrayType>(GEP1->getIndexedType(GEPPointerTy, Indices1, true));
- Indices1.push_back(ConstantSInt::get(Type::LongTy,
- ElTy->getNumElements()-1));
+ 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->getZExtValue() >= AT->getNumElements())
+ return MayAlias; // Be conservative with out-of-range accesses
+ } else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty)) {
+ if (Op1C->getZExtValue() >= PT->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] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
+ else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty))
+ GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,PT->getNumElements()-1);
+
+ }
}
-
- if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op2)) {
- // If this is an array index, make sure the array element is in range...
- if (i != 1) // The pointer index can be "out of range"
- Op1 = CheckArrayIndicesForOverflow(GEPPointerTy, Indices2, Op1C);
- Indices2.push_back((Value*)Op2);
+ 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->getZExtValue() >= AT->getNumElements())
+ return MayAlias; // Be conservative with out-of-range accesses
+ } else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty)) {
+ if (Op2C->getZExtValue() >= PT->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());
+ }
}
- else // Conservatively assume the minimum value for this index
- Indices2.push_back(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;
}
}
-
- int64_t Offset1 = getTargetData().getIndexedOffset(GEPPointerTy, Indices1);
- int64_t Offset2 = getTargetData().getIndexedOffset(GEPPointerTy, Indices2);
- 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;
+
+ if (GEPPointerTy->getElementType()->isSized()) {
+ int64_t Offset1 =
+ getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
+ int64_t Offset2 =
+ getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
+ assert(Offset1<Offset2 && "There is at least one different constant here!");
+
+ if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
+ //cerr << "Determined that these two GEP's don't alias ["
+ // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
+ return NoAlias;
+ }
}
return MayAlias;
}
+namespace {
+ struct VISIBILITY_HIDDEN 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"
+};
+
+static ManagedStatic<std::vector<const char*> > NoMemoryTable;
+static ManagedStatic<std::vector<const char*> > OnlyReadsMemoryTable;
+
+
+AliasAnalysis::ModRefBehavior
+BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
+ std::vector<PointerAccessInfo> *Info) {
+ if (!F->isDeclaration()) return UnknownModRefBehavior;
+
+ 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)
projects / oota-llvm.git / blobdiff