From b307c88fe799eb69c37bee2840d9fde93d407e3a Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Thu, 11 Dec 2003 22:44:13 +0000 Subject: [PATCH] Fix PR86. This makes basicaa _SIGNIFICANLY_ more aggressive with getelementptr's git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10410 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Analysis/BasicAliasAnalysis.cpp | 372 +++++++++++++++++++--------- 1 file changed, 251 insertions(+), 121 deletions(-) diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp index 27b7f5305ec..c886d003d69 100644 --- a/lib/Analysis/BasicAliasAnalysis.cpp +++ b/lib/Analysis/BasicAliasAnalysis.cpp @@ -41,11 +41,14 @@ namespace { AliasResult alias(const Value *V1, unsigned V1Size, const Value *V2, unsigned V2Size); 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, std::vector &GEP1Ops, + unsigned G1Size, + const Type *BasePtr2Ty, std::vector &GEP2Ops, + unsigned G2Size); }; // Register this pass... @@ -89,6 +92,13 @@ static const Value *getUnderlyingObject(const Value *V) { return 0; } +static const User *isGEP(const Value *V) { + if (isa(V) || + (isa(V) && + cast(V)->getOpcode() == Instruction::GetElementPtr)) + return cast(V); + return 0; +} // 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. @@ -97,6 +107,14 @@ static const Value *getUnderlyingObject(const Value *V) { 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(V1)) + if (CE->getOpcode() == Instruction::Cast) + V1 = CE->getOperand(0); + if (const ConstantExpr *CE = dyn_cast(V2)) + if (CE->getOpcode() == Instruction::Cast) + V2 = CE->getOperand(0); + // Strip off constant pointer refs if they exist if (const ConstantPointerRef *CPR = dyn_cast(V1)) V1 = CPR->getValue(); @@ -145,19 +163,67 @@ BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size, return NoAlias; // Unique values don't alias null } - // 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(V1)) - if (const GetElementPtrInst *GEP2 = dyn_cast(V2)) - if (GEP1->getNumOperands() == GEP2->getNumOperands() && - GEP1->getOperand(0)->getType() == GEP2->getOperand(0)->getType()) { - AliasResult GAlias = - CheckGEPInstructions((GetElementPtrInst*)GEP1, V1Size, - (GetElementPtrInst*)GEP2, V2Size); - if (GAlias != MayAlias) - return GAlias; + 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(BasePtr1)->getOperand(0); + } while (isGEP(BasePtr1) && + cast(BasePtr1)->getOperand(1) == + Constant::getNullValue(cast(BasePtr1)->getOperand(1)->getType())); + do { + BasePtr2 = cast(BasePtr2)->getOperand(0); + } while (isGEP(BasePtr2) && + cast(BasePtr2)->getOperand(1) == + Constant::getNullValue(cast(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 GEP1Ops(cast(V1)->op_begin()+1, + cast(V1)->op_end()); + std::vector GEP2Ops(cast(V2)->op_begin()+1, + cast(V2)->op_end()); + + // Accumulate all of the chained indexes into the operand arrays + BasePtr1 = cast(V1)->getOperand(0); + BasePtr2 = cast(V2)->getOperand(0); + while (const User *G = isGEP(BasePtr1)) { + if (!isa(GEP1Ops[0]) || + !cast(GEP1Ops[0])->isNullValue()) + break; // Don't handle folding arbitrary pointer offsets yet... + GEP1Ops.erase(GEP1Ops.begin()); + GEP1Ops.insert(GEP1Ops.begin(), G->op_begin()+1, G->op_end()); + BasePtr1 = G->getOperand(0); } + while (const User *G = isGEP(BasePtr2)) { + if (!isa(GEP2Ops[0]) || + !cast(GEP2Ops[0])->isNullValue()) + break; // Don't handle folding arbitrary pointer offsets yet... + GEP2Ops.erase(GEP2Ops.begin()); + GEP2Ops.insert(GEP2Ops.begin(), G->op_begin()+1, G->op_end()); + BasePtr2 = G->getOperand(0); + } + + 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 @@ -219,45 +285,60 @@ BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size, return MayAlias; } -static Value *CheckArrayIndicesForOverflow(const Type *PtrTy, - const std::vector &Indices, - const ConstantInt *Idx) { - if (const ConstantSInt *IdxS = dyn_cast(Idx)) { - if (IdxS->getValue() < 0) // Underflow on the array subscript? - return Constant::getNullValue(Type::LongTy); - else { // Check for overflow - const ArrayType *ATy = - cast(GetElementPtrInst::getIndexedType(PtrTy, Indices,true)); - if (IdxS->getValue() >= (int64_t)ATy->getNumElements()) - return ConstantSInt::get(Type::LongTy, ATy->getNumElements()-1); +/// 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 &GEP1Ops, + unsigned G1S, + const Type *BasePtr2Ty, std::vector &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 Type *GEPPointerTy = 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 && + GEP1Ops[UnequalOper] == GEP2Ops[UnequalOper]) { + // Advance through the type as we go... + ++UnequalOper; + if (const CompositeType *CT = dyn_cast(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; } } - return (Value*)Idx; // Everything is acceptable. -} -// 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)) - ++UnequalOper; + // 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 && MinOperands != MaxOperands) { + if (GEP1Ops.size() < GEP2Ops.size()) std::swap(GEP1Ops, GEP2Ops); - // If all operands equal each other, then the derived pointers must - // alias each other... - if (UnequalOper == NumGEPOperands) return MustAlias; + bool AllAreZeros = true; + for (unsigned i = UnequalOper; i != MaxOperands; ++i) + if (!isa(GEP1Ops[i]) || + !cast(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 @@ -271,101 +352,150 @@ BasicAliasAnalysis::CheckGEPInstructions(GetElementPtrInst *GEP1, unsigned G1S, // Scan for the first operand that is constant and unequal in the // two getelemenptrs... unsigned FirstConstantOper = UnequalOper; - for (; FirstConstantOper != NumGEPOperands; ++FirstConstantOper) { - const Value *G1Oper = GEP1->getOperand(FirstConstantOper); - const Value *G2Oper = GEP2->getOperand(FirstConstantOper); + for (; FirstConstantOper != MinOperands; ++FirstConstantOper) { + const Value *G1Oper = GEP1Ops[FirstConstantOper]; + const Value *G2Oper = GEP2Ops[FirstConstantOper]; + if (G1Oper != G2Oper && // Found non-equal constant indexes... isa(G1Oper) && isa(G2Oper)) { - // Make sure they are comparable... and make sure the GEP with - // the smaller leading constant is GEP1. - ConstantBool *Compare = - *cast(GEP1->getOperand(FirstConstantOper)) > - *cast(GEP2->getOperand(FirstConstantOper)); + // Make sure they are comparable (ie, not constant expressions)... and + // make sure the GEP with the smaller leading constant is GEP1. + ConstantBool *Compare = *cast(G1Oper) > *cast(G2Oper); if (Compare) { // If they are comparable... if (Compare->getValue()) - std::swap(GEP1, GEP2); // Make GEP1 < GEP2 + std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2 break; } } + BasePtr1Ty = cast(BasePtr1Ty)->getTypeAtIndex(G1Oper); } - // No constant operands, we cannot tell anything... - if (FirstConstantOper == NumGEPOperands) return MayAlias; + // 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. This 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(GEP1Ops[i]) && !isa(GEP1Ops[i]) && + !cast(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(GEP1Ops[i]) || isa(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. - // - std::vector Indices1; - Indices1.reserve(NumGEPOperands-1); - - for (gep_type_iterator I = gep_type_begin(GEP1); - I.getOperandNum() != FirstConstantOper; ++I) - if (isa(*I)) - Indices1.push_back(I.getOperand()); - else - Indices1.push_back(Constant::getNullValue(Type::LongTy)); - - std::vector 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)); + + // Advance BasePtr[12]Ty over this first differing constant operand. + BasePtr2Ty = cast(BasePtr1Ty)->getTypeAtIndex(GEP2Ops[FirstConstantOper]); + BasePtr1Ty = cast(BasePtr1Ty)->getTypeAtIndex(GEP1Ops[FirstConstantOper]); - const Type *GEPPointerTy = GEP1->getOperand(0)->getType(); + // 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 equal sequence of variables into constant zeros to start with. + for (unsigned i = 0; i != FirstConstantOper; ++i) { + if (!isa(GEP1Ops[i]) || isa(GEP1Ops[i]) || + !isa(GEP2Ops[i]) || isa(GEP2Ops[i])) { + GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType()); + GEP2Ops[i] = Constant::getNullValue(GEP2Ops[i]->getType()); + } + } + + // 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... - if (!isa(Op1)) { - Indices1.push_back(Constant::getNullValue(Op1->getType())); - Indices2.push_back(Indices1.back()); - } else { - Indices1.push_back((Value*)Op1); - Indices2.push_back((Value*)Op2); - } + 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(Op1) || isa(Op1)) + GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType()); + // Otherwise, just keep the constants we have. } else { - if (const ConstantInt *Op1C = dyn_cast(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(GEP1->getIndexedType(GEPPointerTy, Indices1, true)); - Indices1.push_back(ConstantSInt::get(Type::LongTy, - ElTy->getNumElements()-1)); + if (Op1) { + if (const ConstantInt *Op1C = dyn_cast(Op1)) { + // If this is an array index, make sure the array element is in range. + if (const ArrayType *AT = dyn_cast(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(BasePtr1Ty)) + GEP1Ops[i] = ConstantSInt::get(Type::LongTy,AT->getNumElements()-1); + } } - if (const ConstantInt *Op1C = dyn_cast(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(Op2)) { + // If this is an array index, make sure the array element is in range. + if (const ArrayType *AT = dyn_cast(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()); + } } - 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(BasePtr1Ty)) + BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]); + else + BasePtr1Ty = 0; + } + + if (BasePtr2Ty && Op2) { + if (const CompositeType *CT = dyn_cast(BasePtr2Ty)) + BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]); + else + BasePtr2Ty = 0; } } - int64_t Offset1 = getTargetData().getIndexedOffset(GEPPointerTy, Indices1); - int64_t Offset2 = getTargetData().getIndexedOffset(GEPPointerTy, Indices2); + 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) { -- 2.34.1