| //===-- ConstantFolding.cpp - Analyze constant folding possibilities ------===// |
| // |
| // 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 family of functions determines the possibility of performing constant |
| // folding. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Analysis/ConstantFolding.h" |
| #include "llvm/Constants.h" |
| #include "llvm/DerivedTypes.h" |
| #include "llvm/Function.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/Intrinsics.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/StringMap.h" |
| #include "llvm/Target/TargetData.h" |
| #include "llvm/Support/GetElementPtrTypeIterator.h" |
| #include "llvm/Support/MathExtras.h" |
| #include <cerrno> |
| #include <cmath> |
| using namespace llvm; |
| |
| //===----------------------------------------------------------------------===// |
| // Constant Folding internal helper functions |
| //===----------------------------------------------------------------------===// |
| |
| /// IsConstantOffsetFromGlobal - If this constant is actually a constant offset |
| /// from a global, return the global and the constant. Because of |
| /// constantexprs, this function is recursive. |
| static bool IsConstantOffsetFromGlobal(Constant *C, GlobalValue *&GV, |
| int64_t &Offset, const TargetData &TD) { |
| // Trivial case, constant is the global. |
| if ((GV = dyn_cast<GlobalValue>(C))) { |
| Offset = 0; |
| return true; |
| } |
| |
| // Otherwise, if this isn't a constant expr, bail out. |
| ConstantExpr *CE = dyn_cast<ConstantExpr>(C); |
| if (!CE) return false; |
| |
| // Look through ptr->int and ptr->ptr casts. |
| if (CE->getOpcode() == Instruction::PtrToInt || |
| CE->getOpcode() == Instruction::BitCast) |
| return IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD); |
| |
| // i32* getelementptr ([5 x i32]* @a, i32 0, i32 5) |
| if (CE->getOpcode() == Instruction::GetElementPtr) { |
| // Cannot compute this if the element type of the pointer is missing size |
| // info. |
| if (!cast<PointerType>(CE->getOperand(0)->getType())->getElementType()->isSized()) |
| return false; |
| |
| // If the base isn't a global+constant, we aren't either. |
| if (!IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD)) |
| return false; |
| |
| // Otherwise, add any offset that our operands provide. |
| gep_type_iterator GTI = gep_type_begin(CE); |
| for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i, ++GTI) { |
| ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(i)); |
| if (!CI) return false; // Index isn't a simple constant? |
| if (CI->getZExtValue() == 0) continue; // Not adding anything. |
| |
| if (const StructType *ST = dyn_cast<StructType>(*GTI)) { |
| // N = N + Offset |
| Offset += TD.getStructLayout(ST)->getElementOffset(CI->getZExtValue()); |
| } else { |
| const SequentialType *SQT = cast<SequentialType>(*GTI); |
| Offset += TD.getTypeSize(SQT->getElementType())*CI->getSExtValue(); |
| } |
| } |
| return true; |
| } |
| |
| return false; |
| } |
| |
| |
| /// SymbolicallyEvaluateBinop - One of Op0/Op1 is a constant expression. |
| /// Attempt to symbolically evaluate the result of a binary operator merging |
| /// these together. If target data info is available, it is provided as TD, |
| /// otherwise TD is null. |
| static Constant *SymbolicallyEvaluateBinop(unsigned Opc, Constant *Op0, |
| Constant *Op1, const TargetData *TD){ |
| // SROA |
| |
| // Fold (and 0xffffffff00000000, (shl x, 32)) -> shl. |
| // Fold (lshr (or X, Y), 32) -> (lshr [X/Y], 32) if one doesn't contribute |
| // bits. |
| |
| |
| // If the constant expr is something like &A[123] - &A[4].f, fold this into a |
| // constant. This happens frequently when iterating over a global array. |
| if (Opc == Instruction::Sub && TD) { |
| GlobalValue *GV1, *GV2; |
| int64_t Offs1, Offs2; |
| |
| if (IsConstantOffsetFromGlobal(Op0, GV1, Offs1, *TD)) |
| if (IsConstantOffsetFromGlobal(Op1, GV2, Offs2, *TD) && |
| GV1 == GV2) { |
| // (&GV+C1) - (&GV+C2) -> C1-C2, pointer arithmetic cannot overflow. |
| return ConstantInt::get(Op0->getType(), Offs1-Offs2); |
| } |
| } |
| |
| // TODO: Fold icmp setne/seteq as well. |
| return 0; |
| } |
| |
| /// SymbolicallyEvaluateGEP - If we can symbolically evaluate the specified GEP |
| /// constant expression, do so. |
| static Constant *SymbolicallyEvaluateGEP(Constant** Ops, unsigned NumOps, |
| const Type *ResultTy, |
| const TargetData *TD) { |
| Constant *Ptr = Ops[0]; |
| if (!cast<PointerType>(Ptr->getType())->getElementType()->isSized()) |
| return 0; |
| |
| if (TD && Ptr->isNullValue()) { |
| // If this is a constant expr gep that is effectively computing an |
| // "offsetof", fold it into 'cast int Size to T*' instead of 'gep 0, 0, 12' |
| bool isFoldableGEP = true; |
| for (unsigned i = 1; i != NumOps; ++i) |
| if (!isa<ConstantInt>(Ops[i])) { |
| isFoldableGEP = false; |
| break; |
| } |
| if (isFoldableGEP) { |
| uint64_t Offset = TD->getIndexedOffset(Ptr->getType(), |
| (Value**)Ops+1, NumOps-1); |
| Constant *C = ConstantInt::get(TD->getIntPtrType(), Offset); |
| return ConstantExpr::getIntToPtr(C, ResultTy); |
| } |
| } |
| |
| return 0; |
| } |
| |
| |
| //===----------------------------------------------------------------------===// |
| // Constant Folding public APIs |
| //===----------------------------------------------------------------------===// |
| |
| |
| /// ConstantFoldInstruction - Attempt to constant fold the specified |
| /// instruction. If successful, the constant result is returned, if not, null |
| /// is returned. Note that this function can only fail when attempting to fold |
| /// instructions like loads and stores, which have no constant expression form. |
| /// |
| Constant *llvm::ConstantFoldInstruction(Instruction *I, const TargetData *TD) { |
| if (PHINode *PN = dyn_cast<PHINode>(I)) { |
| if (PN->getNumIncomingValues() == 0) |
| return Constant::getNullValue(PN->getType()); |
| |
| Constant *Result = dyn_cast<Constant>(PN->getIncomingValue(0)); |
| if (Result == 0) return 0; |
| |
| // Handle PHI nodes specially here... |
| for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) |
| if (PN->getIncomingValue(i) != Result && PN->getIncomingValue(i) != PN) |
| return 0; // Not all the same incoming constants... |
| |
| // If we reach here, all incoming values are the same constant. |
| return Result; |
| } |
| |
| // Scan the operand list, checking to see if they are all constants, if so, |
| // hand off to ConstantFoldInstOperands. |
| SmallVector<Constant*, 8> Ops; |
| for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) |
| if (Constant *Op = dyn_cast<Constant>(I->getOperand(i))) |
| Ops.push_back(Op); |
| else |
| return 0; // All operands not constant! |
| |
| return ConstantFoldInstOperands(I, &Ops[0], Ops.size(), TD); |
| } |
| |
| /// ConstantFoldInstOperands - Attempt to constant fold an instruction with the |
| /// specified opcode and operands. If successful, the constant result is |
| /// returned, if not, null is returned. Note that this function can fail when |
| /// attempting to fold instructions like loads and stores, which have no |
| /// constant expression form. |
| /// |
| Constant *llvm::ConstantFoldInstOperands(const Instruction* I, |
| Constant** Ops, unsigned NumOps, |
| const TargetData *TD) { |
| unsigned Opc = I->getOpcode(); |
| const Type *DestTy = I->getType(); |
| |
| // Handle easy binops first. |
| if (isa<BinaryOperator>(I)) { |
| if (isa<ConstantExpr>(Ops[0]) || isa<ConstantExpr>(Ops[1])) |
| if (Constant *C = SymbolicallyEvaluateBinop(I->getOpcode(), Ops[0], |
| Ops[1], TD)) |
| return C; |
| |
| return ConstantExpr::get(Opc, Ops[0], Ops[1]); |
| } |
| |
| switch (Opc) { |
| default: return 0; |
| case Instruction::Call: |
| if (Function *F = dyn_cast<Function>(Ops[0])) |
| if (canConstantFoldCallTo(F)) |
| return ConstantFoldCall(F, Ops+1, NumOps-1); |
| return 0; |
| case Instruction::ICmp: |
| case Instruction::FCmp: |
| return ConstantExpr::getCompare(cast<CmpInst>(I)->getPredicate(), Ops[0], |
| Ops[1]); |
| case Instruction::PtrToInt: |
| // If the input is a inttoptr, eliminate the pair. This requires knowing |
| // the width of a pointer, so it can't be done in ConstantExpr::getCast. |
| if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ops[0])) { |
| if (TD && CE->getOpcode() == Instruction::IntToPtr) { |
| Constant *Input = CE->getOperand(0); |
| unsigned InWidth = Input->getType()->getPrimitiveSizeInBits(); |
| Constant *Mask = |
| ConstantInt::get(APInt::getLowBitsSet(InWidth, |
| TD->getPointerSizeInBits())); |
| Input = ConstantExpr::getAnd(Input, Mask); |
| // Do a zext or trunc to get to the dest size. |
| return ConstantExpr::getIntegerCast(Input, I->getType(), false); |
| } |
| } |
| // FALL THROUGH. |
| case Instruction::IntToPtr: |
| case Instruction::Trunc: |
| case Instruction::ZExt: |
| case Instruction::SExt: |
| case Instruction::FPTrunc: |
| case Instruction::FPExt: |
| case Instruction::UIToFP: |
| case Instruction::SIToFP: |
| case Instruction::FPToUI: |
| case Instruction::FPToSI: |
| case Instruction::BitCast: |
| return ConstantExpr::getCast(Opc, Ops[0], DestTy); |
| case Instruction::Select: |
| return ConstantExpr::getSelect(Ops[0], Ops[1], Ops[2]); |
| case Instruction::ExtractElement: |
| return ConstantExpr::getExtractElement(Ops[0], Ops[1]); |
| case Instruction::InsertElement: |
| return ConstantExpr::getInsertElement(Ops[0], Ops[1], Ops[2]); |
| case Instruction::ShuffleVector: |
| return ConstantExpr::getShuffleVector(Ops[0], Ops[1], Ops[2]); |
| case Instruction::GetElementPtr: |
| if (Constant *C = SymbolicallyEvaluateGEP(Ops, NumOps, I->getType(), TD)) |
| return C; |
| |
| return ConstantExpr::getGetElementPtr(Ops[0], Ops+1, NumOps-1); |
| } |
| } |
| |
| /// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a |
| /// getelementptr constantexpr, return the constant value being addressed by the |
| /// constant expression, or null if something is funny and we can't decide. |
| Constant *llvm::ConstantFoldLoadThroughGEPConstantExpr(Constant *C, |
| ConstantExpr *CE) { |
| if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType())) |
| return 0; // Do not allow stepping over the value! |
| |
| // Loop over all of the operands, tracking down which value we are |
| // addressing... |
| gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE); |
| for (++I; I != E; ++I) |
| if (const StructType *STy = dyn_cast<StructType>(*I)) { |
| ConstantInt *CU = cast<ConstantInt>(I.getOperand()); |
| assert(CU->getZExtValue() < STy->getNumElements() && |
| "Struct index out of range!"); |
| unsigned El = (unsigned)CU->getZExtValue(); |
| if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) { |
| C = CS->getOperand(El); |
| } else if (isa<ConstantAggregateZero>(C)) { |
| C = Constant::getNullValue(STy->getElementType(El)); |
| } else if (isa<UndefValue>(C)) { |
| C = UndefValue::get(STy->getElementType(El)); |
| } else { |
| return 0; |
| } |
| } else if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) { |
| if (const ArrayType *ATy = dyn_cast<ArrayType>(*I)) { |
| if (CI->getZExtValue() >= ATy->getNumElements()) |
| return 0; |
| if (ConstantArray *CA = dyn_cast<ConstantArray>(C)) |
| C = CA->getOperand(CI->getZExtValue()); |
| else if (isa<ConstantAggregateZero>(C)) |
| C = Constant::getNullValue(ATy->getElementType()); |
| else if (isa<UndefValue>(C)) |
| C = UndefValue::get(ATy->getElementType()); |
| else |
| return 0; |
| } else if (const VectorType *PTy = dyn_cast<VectorType>(*I)) { |
| if (CI->getZExtValue() >= PTy->getNumElements()) |
| return 0; |
| if (ConstantVector *CP = dyn_cast<ConstantVector>(C)) |
| C = CP->getOperand(CI->getZExtValue()); |
| else if (isa<ConstantAggregateZero>(C)) |
| C = Constant::getNullValue(PTy->getElementType()); |
| else if (isa<UndefValue>(C)) |
| C = UndefValue::get(PTy->getElementType()); |
| else |
| return 0; |
| } else { |
| return 0; |
| } |
| } else { |
| return 0; |
| } |
| return C; |
| } |
| |
| |
| //===----------------------------------------------------------------------===// |
| // Constant Folding for Calls |
| // |
| |
| /// canConstantFoldCallTo - Return true if its even possible to fold a call to |
| /// the specified function. |
| bool |
| llvm::canConstantFoldCallTo(Function *F) { |
| switch (F->getIntrinsicID()) { |
| case Intrinsic::sqrt_f32: |
| case Intrinsic::sqrt_f64: |
| case Intrinsic::powi_f32: |
| case Intrinsic::powi_f64: |
| case Intrinsic::bswap: |
| case Intrinsic::ctpop: |
| case Intrinsic::ctlz: |
| case Intrinsic::cttz: |
| return true; |
| default: break; |
| } |
| |
| const ValueName *NameVal = F->getValueName(); |
| if (NameVal == 0) return false; |
| const char *Str = NameVal->getKeyData(); |
| unsigned Len = NameVal->getKeyLength(); |
| |
| // In these cases, the check of the length is required. We don't want to |
| // return true for a name like "cos\0blah" which strcmp would return equal to |
| // "cos", but has length 8. |
| switch (Str[0]) { |
| default: return false; |
| case 'a': |
| if (Len == 4) |
| return !strcmp(Str, "acos") || !strcmp(Str, "asin") || |
| !strcmp(Str, "atan"); |
| else if (Len == 5) |
| return !strcmp(Str, "atan2"); |
| return false; |
| case 'c': |
| if (Len == 3) |
| return !strcmp(Str, "cos"); |
| else if (Len == 4) |
| return !strcmp(Str, "ceil") || !strcmp(Str, "cosf") || |
| !strcmp(Str, "cosh"); |
| return false; |
| case 'e': |
| if (Len == 3) |
| return !strcmp(Str, "exp"); |
| return false; |
| case 'f': |
| if (Len == 4) |
| return !strcmp(Str, "fabs") || !strcmp(Str, "fmod"); |
| else if (Len == 5) |
| return !strcmp(Str, "floor"); |
| return false; |
| break; |
| case 'l': |
| if (Len == 3 && !strcmp(Str, "log")) |
| return true; |
| if (Len == 5 && !strcmp(Str, "log10")) |
| return true; |
| return false; |
| case 'p': |
| if (Len == 3 && !strcmp(Str, "pow")) |
| return true; |
| return false; |
| case 's': |
| if (Len == 3) |
| return !strcmp(Str, "sin"); |
| if (Len == 4) |
| return !strcmp(Str, "sinh") || !strcmp(Str, "sqrt"); |
| if (Len == 5) |
| return !strcmp(Str, "sqrtf"); |
| return false; |
| case 't': |
| if (Len == 3 && !strcmp(Str, "tan")) |
| return true; |
| else if (Len == 4 && !strcmp(Str, "tanh")) |
| return true; |
| return false; |
| } |
| } |
| |
| static Constant *ConstantFoldFP(double (*NativeFP)(double), double V, |
| const Type *Ty) { |
| errno = 0; |
| V = NativeFP(V); |
| if (errno == 0) { |
| if (Ty==Type::FloatTy) |
| return ConstantFP::get(Ty, APFloat((float)V)); |
| else if (Ty==Type::DoubleTy) |
| return ConstantFP::get(Ty, APFloat(V)); |
| else |
| assert(0); |
| } |
| errno = 0; |
| return 0; |
| } |
| |
| static Constant *ConstantFoldBinaryFP(double (*NativeFP)(double, double), |
| double V, double W, |
| const Type *Ty) { |
| errno = 0; |
| V = NativeFP(V, W); |
| if (errno == 0) { |
| if (Ty==Type::FloatTy) |
| return ConstantFP::get(Ty, APFloat((float)V)); |
| else if (Ty==Type::DoubleTy) |
| return ConstantFP::get(Ty, APFloat(V)); |
| else |
| assert(0); |
| } |
| errno = 0; |
| return 0; |
| } |
| |
| /// ConstantFoldCall - Attempt to constant fold a call to the specified function |
| /// with the specified arguments, returning null if unsuccessful. |
| |
| Constant * |
| llvm::ConstantFoldCall(Function *F, Constant** Operands, unsigned NumOperands) { |
| const ValueName *NameVal = F->getValueName(); |
| if (NameVal == 0) return 0; |
| const char *Str = NameVal->getKeyData(); |
| unsigned Len = NameVal->getKeyLength(); |
| |
| const Type *Ty = F->getReturnType(); |
| if (NumOperands == 1) { |
| if (ConstantFP *Op = dyn_cast<ConstantFP>(Operands[0])) { |
| if (Ty!=Type::FloatTy && Ty!=Type::DoubleTy) |
| return 0; |
| /// Currently APFloat versions of these functions do not exist, so we use |
| /// the host native double versions. Float versions are not called |
| /// directly but for all these it is true (float)(f((double)arg)) == |
| /// f(arg). Long double not supported yet. |
| double V = Ty==Type::FloatTy ? (double)Op->getValueAPF().convertToFloat(): |
| Op->getValueAPF().convertToDouble(); |
| switch (Str[0]) { |
| case 'a': |
| if (Len == 4 && !strcmp(Str, "acos")) |
| return ConstantFoldFP(acos, V, Ty); |
| else if (Len == 4 && !strcmp(Str, "asin")) |
| return ConstantFoldFP(asin, V, Ty); |
| else if (Len == 4 && !strcmp(Str, "atan")) |
| return ConstantFoldFP(atan, V, Ty); |
| break; |
| case 'c': |
| if (Len == 4 && !strcmp(Str, "ceil")) |
| return ConstantFoldFP(ceil, V, Ty); |
| else if (Len == 3 && !strcmp(Str, "cos")) |
| return ConstantFoldFP(cos, V, Ty); |
| else if (Len == 4 && !strcmp(Str, "cosh")) |
| return ConstantFoldFP(cosh, V, Ty); |
| break; |
| case 'e': |
| if (Len == 3 && !strcmp(Str, "exp")) |
| return ConstantFoldFP(exp, V, Ty); |
| break; |
| case 'f': |
| if (Len == 4 && !strcmp(Str, "fabs")) |
| return ConstantFoldFP(fabs, V, Ty); |
| else if (Len == 5 && !strcmp(Str, "floor")) |
| return ConstantFoldFP(floor, V, Ty); |
| break; |
| case 'l': |
| if (Len == 3 && !strcmp(Str, "log") && V > 0) |
| return ConstantFoldFP(log, V, Ty); |
| else if (Len == 5 && !strcmp(Str, "log10") && V > 0) |
| return ConstantFoldFP(log10, V, Ty); |
| else if (!strcmp(Str, "llvm.sqrt.f32") || |
| !strcmp(Str, "llvm.sqrt.f64")) { |
| if (V >= -0.0) |
| return ConstantFoldFP(sqrt, V, Ty); |
| else // Undefined |
| return ConstantFP::get(Ty, Ty==Type::FloatTy ? APFloat(0.0f) : |
| APFloat(0.0)); |
| } |
| break; |
| case 's': |
| if (Len == 3 && !strcmp(Str, "sin")) |
| return ConstantFoldFP(sin, V, Ty); |
| else if (Len == 4 && !strcmp(Str, "sinh")) |
| return ConstantFoldFP(sinh, V, Ty); |
| else if (Len == 4 && !strcmp(Str, "sqrt") && V >= 0) |
| return ConstantFoldFP(sqrt, V, Ty); |
| else if (Len == 5 && !strcmp(Str, "sqrtf") && V >= 0) |
| return ConstantFoldFP(sqrt, V, Ty); |
| break; |
| case 't': |
| if (Len == 3 && !strcmp(Str, "tan")) |
| return ConstantFoldFP(tan, V, Ty); |
| else if (Len == 4 && !strcmp(Str, "tanh")) |
| return ConstantFoldFP(tanh, V, Ty); |
| break; |
| default: |
| break; |
| } |
| } else if (ConstantInt *Op = dyn_cast<ConstantInt>(Operands[0])) { |
| if (Len > 11 && !memcmp(Str, "llvm.bswap", 10)) { |
| return ConstantInt::get(Op->getValue().byteSwap()); |
| } else if (Len > 11 && !memcmp(Str, "llvm.ctpop", 10)) { |
| uint64_t ctpop = Op->getValue().countPopulation(); |
| return ConstantInt::get(Ty, ctpop); |
| } else if (Len > 10 && !memcmp(Str, "llvm.cttz", 9)) { |
| uint64_t cttz = Op->getValue().countTrailingZeros(); |
| return ConstantInt::get(Ty, cttz); |
| } else if (Len > 10 && !memcmp(Str, "llvm.ctlz", 9)) { |
| uint64_t ctlz = Op->getValue().countLeadingZeros(); |
| return ConstantInt::get(Ty, ctlz); |
| } |
| } |
| } else if (NumOperands == 2) { |
| if (ConstantFP *Op1 = dyn_cast<ConstantFP>(Operands[0])) { |
| double Op1V = Ty==Type::FloatTy ? |
| (double)Op1->getValueAPF().convertToFloat(): |
| Op1->getValueAPF().convertToDouble(); |
| if (ConstantFP *Op2 = dyn_cast<ConstantFP>(Operands[1])) { |
| if (Ty!=Type::FloatTy && Ty!=Type::DoubleTy) |
| return 0; |
| double Op2V = Ty==Type::FloatTy ? |
| (double)Op2->getValueAPF().convertToFloat(): |
| Op2->getValueAPF().convertToDouble(); |
| |
| if (Len == 3 && !strcmp(Str, "pow")) { |
| return ConstantFoldBinaryFP(pow, Op1V, Op2V, Ty); |
| } else if (Len == 4 && !strcmp(Str, "fmod")) { |
| return ConstantFoldBinaryFP(fmod, Op1V, Op2V, Ty); |
| } else if (Len == 5 && !strcmp(Str, "atan2")) { |
| return ConstantFoldBinaryFP(atan2, Op1V, Op2V, Ty); |
| } |
| } else if (ConstantInt *Op2C = dyn_cast<ConstantInt>(Operands[1])) { |
| if (!strcmp(Str, "llvm.powi.f32")) { |
| return ConstantFP::get(Ty, APFloat((float)std::pow((float)Op1V, |
| (int)Op2C->getZExtValue()))); |
| } else if (!strcmp(Str, "llvm.powi.f64")) { |
| return ConstantFP::get(Ty, APFloat((double)std::pow((double)Op1V, |
| (int)Op2C->getZExtValue()))); |
| } |
| } |
| } |
| } |
| return 0; |
| } |
| |
