//===-- ConstantFolding.cpp - Fold instructions into constants ------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file defines routines for folding instructions into constants. // // Also, to supplement the basic VMCore ConstantExpr simplifications, // this file defines some additional folding routines that can make use of // TargetData information. These functions cannot go in VMCore due to library // dependency issues. // //===----------------------------------------------------------------------===// #include "llvm/Analysis/ConstantFolding.h" #include "llvm/Constants.h" #include "llvm/DerivedTypes.h" #include "llvm/Function.h" #include "llvm/GlobalVariable.h" #include "llvm/Instructions.h" #include "llvm/Intrinsics.h" #include "llvm/Analysis/ValueTracking.h" #include "llvm/Target/TargetData.h" #include "llvm/ADT/SmallVector.h" #include "llvm/ADT/StringMap.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/GetElementPtrTypeIterator.h" #include "llvm/Support/MathExtras.h" #include "llvm/Support/FEnv.h" #include #include using namespace llvm; //===----------------------------------------------------------------------===// // Constant Folding internal helper functions //===----------------------------------------------------------------------===// /// FoldBitCast - Constant fold bitcast, symbolically evaluating it with /// TargetData. This always returns a non-null constant, but it may be a /// ConstantExpr if unfoldable. static Constant *FoldBitCast(Constant *C, const Type *DestTy, const TargetData &TD) { // This only handles casts to vectors currently. const VectorType *DestVTy = dyn_cast(DestTy); if (DestVTy == 0) return ConstantExpr::getBitCast(C, DestTy); // If this is a scalar -> vector cast, convert the input into a <1 x scalar> // vector so the code below can handle it uniformly. if (isa(C) || isa(C)) { Constant *Ops = C; // don't take the address of C! return FoldBitCast(ConstantVector::get(&Ops, 1), DestTy, TD); } // If this is a bitcast from constant vector -> vector, fold it. ConstantVector *CV = dyn_cast(C); if (CV == 0) return ConstantExpr::getBitCast(C, DestTy); // If the element types match, VMCore can fold it. unsigned NumDstElt = DestVTy->getNumElements(); unsigned NumSrcElt = CV->getNumOperands(); if (NumDstElt == NumSrcElt) return ConstantExpr::getBitCast(C, DestTy); const Type *SrcEltTy = CV->getType()->getElementType(); const Type *DstEltTy = DestVTy->getElementType(); // Otherwise, we're changing the number of elements in a vector, which // requires endianness information to do the right thing. For example, // bitcast (<2 x i64> to <4 x i32>) // folds to (little endian): // <4 x i32> // and to (big endian): // <4 x i32> // First thing is first. We only want to think about integer here, so if // we have something in FP form, recast it as integer. if (DstEltTy->isFloatingPointTy()) { // Fold to an vector of integers with same size as our FP type. unsigned FPWidth = DstEltTy->getPrimitiveSizeInBits(); const Type *DestIVTy = VectorType::get(IntegerType::get(C->getContext(), FPWidth), NumDstElt); // Recursively handle this integer conversion, if possible. C = FoldBitCast(C, DestIVTy, TD); if (!C) return ConstantExpr::getBitCast(C, DestTy); // Finally, VMCore can handle this now that #elts line up. return ConstantExpr::getBitCast(C, DestTy); } // Okay, we know the destination is integer, if the input is FP, convert // it to integer first. if (SrcEltTy->isFloatingPointTy()) { unsigned FPWidth = SrcEltTy->getPrimitiveSizeInBits(); const Type *SrcIVTy = VectorType::get(IntegerType::get(C->getContext(), FPWidth), NumSrcElt); // Ask VMCore to do the conversion now that #elts line up. C = ConstantExpr::getBitCast(C, SrcIVTy); CV = dyn_cast(C); if (!CV) // If VMCore wasn't able to fold it, bail out. return C; } // Now we know that the input and output vectors are both integer vectors // of the same size, and that their #elements is not the same. Do the // conversion here, which depends on whether the input or output has // more elements. bool isLittleEndian = TD.isLittleEndian(); SmallVector Result; if (NumDstElt < NumSrcElt) { // Handle: bitcast (<4 x i32> to <2 x i64>) Constant *Zero = Constant::getNullValue(DstEltTy); unsigned Ratio = NumSrcElt/NumDstElt; unsigned SrcBitSize = SrcEltTy->getPrimitiveSizeInBits(); unsigned SrcElt = 0; for (unsigned i = 0; i != NumDstElt; ++i) { // Build each element of the result. Constant *Elt = Zero; unsigned ShiftAmt = isLittleEndian ? 0 : SrcBitSize*(Ratio-1); for (unsigned j = 0; j != Ratio; ++j) { Constant *Src = dyn_cast(CV->getOperand(SrcElt++)); if (!Src) // Reject constantexpr elements. return ConstantExpr::getBitCast(C, DestTy); // Zero extend the element to the right size. Src = ConstantExpr::getZExt(Src, Elt->getType()); // Shift it to the right place, depending on endianness. Src = ConstantExpr::getShl(Src, ConstantInt::get(Src->getType(), ShiftAmt)); ShiftAmt += isLittleEndian ? SrcBitSize : -SrcBitSize; // Mix it in. Elt = ConstantExpr::getOr(Elt, Src); } Result.push_back(Elt); } } else { // Handle: bitcast (<2 x i64> to <4 x i32>) unsigned Ratio = NumDstElt/NumSrcElt; unsigned DstBitSize = DstEltTy->getPrimitiveSizeInBits(); // Loop over each source value, expanding into multiple results. for (unsigned i = 0; i != NumSrcElt; ++i) { Constant *Src = dyn_cast(CV->getOperand(i)); if (!Src) // Reject constantexpr elements. return ConstantExpr::getBitCast(C, DestTy); unsigned ShiftAmt = isLittleEndian ? 0 : DstBitSize*(Ratio-1); for (unsigned j = 0; j != Ratio; ++j) { // Shift the piece of the value into the right place, depending on // endianness. Constant *Elt = ConstantExpr::getLShr(Src, ConstantInt::get(Src->getType(), ShiftAmt)); ShiftAmt += isLittleEndian ? DstBitSize : -DstBitSize; // Truncate and remember this piece. Result.push_back(ConstantExpr::getTrunc(Elt, DstEltTy)); } } } return ConstantVector::get(Result.data(), Result.size()); } /// 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(C))) { Offset = 0; return true; } // Otherwise, if this isn't a constant expr, bail out. ConstantExpr *CE = dyn_cast(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(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 (User::const_op_iterator i = CE->op_begin() + 1, e = CE->op_end(); i != e; ++i, ++GTI) { ConstantInt *CI = dyn_cast(*i); if (!CI) return false; // Index isn't a simple constant? if (CI->isZero()) continue; // Not adding anything. if (const StructType *ST = dyn_cast(*GTI)) { // N = N + Offset Offset += TD.getStructLayout(ST)->getElementOffset(CI->getZExtValue()); } else { const SequentialType *SQT = cast(*GTI); Offset += TD.getTypeAllocSize(SQT->getElementType())*CI->getSExtValue(); } } return true; } return false; } /// ReadDataFromGlobal - Recursive helper to read bits out of global. C is the /// constant being copied out of. ByteOffset is an offset into C. CurPtr is the /// pointer to copy results into and BytesLeft is the number of bytes left in /// the CurPtr buffer. TD is the target data. static bool ReadDataFromGlobal(Constant *C, uint64_t ByteOffset, unsigned char *CurPtr, unsigned BytesLeft, const TargetData &TD) { assert(ByteOffset <= TD.getTypeAllocSize(C->getType()) && "Out of range access"); // If this element is zero or undefined, we can just return since *CurPtr is // zero initialized. if (isa(C) || isa(C)) return true; if (ConstantInt *CI = dyn_cast(C)) { if (CI->getBitWidth() > 64 || (CI->getBitWidth() & 7) != 0) return false; uint64_t Val = CI->getZExtValue(); unsigned IntBytes = unsigned(CI->getBitWidth()/8); for (unsigned i = 0; i != BytesLeft && ByteOffset != IntBytes; ++i) { CurPtr[i] = (unsigned char)(Val >> (ByteOffset * 8)); ++ByteOffset; } return true; } if (ConstantFP *CFP = dyn_cast(C)) { if (CFP->getType()->isDoubleTy()) { C = FoldBitCast(C, Type::getInt64Ty(C->getContext()), TD); return ReadDataFromGlobal(C, ByteOffset, CurPtr, BytesLeft, TD); } if (CFP->getType()->isFloatTy()){ C = FoldBitCast(C, Type::getInt32Ty(C->getContext()), TD); return ReadDataFromGlobal(C, ByteOffset, CurPtr, BytesLeft, TD); } return false; } if (ConstantStruct *CS = dyn_cast(C)) { const StructLayout *SL = TD.getStructLayout(CS->getType()); unsigned Index = SL->getElementContainingOffset(ByteOffset); uint64_t CurEltOffset = SL->getElementOffset(Index); ByteOffset -= CurEltOffset; while (1) { // If the element access is to the element itself and not to tail padding, // read the bytes from the element. uint64_t EltSize = TD.getTypeAllocSize(CS->getOperand(Index)->getType()); if (ByteOffset < EltSize && !ReadDataFromGlobal(CS->getOperand(Index), ByteOffset, CurPtr, BytesLeft, TD)) return false; ++Index; // Check to see if we read from the last struct element, if so we're done. if (Index == CS->getType()->getNumElements()) return true; // If we read all of the bytes we needed from this element we're done. uint64_t NextEltOffset = SL->getElementOffset(Index); if (BytesLeft <= NextEltOffset-CurEltOffset-ByteOffset) return true; // Move to the next element of the struct. CurPtr += NextEltOffset-CurEltOffset-ByteOffset; BytesLeft -= NextEltOffset-CurEltOffset-ByteOffset; ByteOffset = 0; CurEltOffset = NextEltOffset; } // not reached. } if (ConstantArray *CA = dyn_cast(C)) { uint64_t EltSize = TD.getTypeAllocSize(CA->getType()->getElementType()); uint64_t Index = ByteOffset / EltSize; uint64_t Offset = ByteOffset - Index * EltSize; for (; Index != CA->getType()->getNumElements(); ++Index) { if (!ReadDataFromGlobal(CA->getOperand(Index), Offset, CurPtr, BytesLeft, TD)) return false; if (EltSize >= BytesLeft) return true; Offset = 0; BytesLeft -= EltSize; CurPtr += EltSize; } return true; } if (ConstantVector *CV = dyn_cast(C)) { uint64_t EltSize = TD.getTypeAllocSize(CV->getType()->getElementType()); uint64_t Index = ByteOffset / EltSize; uint64_t Offset = ByteOffset - Index * EltSize; for (; Index != CV->getType()->getNumElements(); ++Index) { if (!ReadDataFromGlobal(CV->getOperand(Index), Offset, CurPtr, BytesLeft, TD)) return false; if (EltSize >= BytesLeft) return true; Offset = 0; BytesLeft -= EltSize; CurPtr += EltSize; } return true; } // Otherwise, unknown initializer type. return false; } static Constant *FoldReinterpretLoadFromConstPtr(Constant *C, const TargetData &TD) { const Type *LoadTy = cast(C->getType())->getElementType(); const IntegerType *IntType = dyn_cast(LoadTy); // If this isn't an integer load we can't fold it directly. if (!IntType) { // If this is a float/double load, we can try folding it as an int32/64 load // and then bitcast the result. This can be useful for union cases. Note // that address spaces don't matter here since we're not going to result in // an actual new load. const Type *MapTy; if (LoadTy->isFloatTy()) MapTy = Type::getInt32PtrTy(C->getContext()); else if (LoadTy->isDoubleTy()) MapTy = Type::getInt64PtrTy(C->getContext()); else if (LoadTy->isVectorTy()) { MapTy = IntegerType::get(C->getContext(), TD.getTypeAllocSizeInBits(LoadTy)); MapTy = PointerType::getUnqual(MapTy); } else return 0; C = FoldBitCast(C, MapTy, TD); if (Constant *Res = FoldReinterpretLoadFromConstPtr(C, TD)) return FoldBitCast(Res, LoadTy, TD); return 0; } unsigned BytesLoaded = (IntType->getBitWidth() + 7) / 8; if (BytesLoaded > 32 || BytesLoaded == 0) return 0; GlobalValue *GVal; int64_t Offset; if (!IsConstantOffsetFromGlobal(C, GVal, Offset, TD)) return 0; GlobalVariable *GV = dyn_cast(GVal); if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer() || !GV->getInitializer()->getType()->isSized()) return 0; // If we're loading off the beginning of the global, some bytes may be valid, // but we don't try to handle this. if (Offset < 0) return 0; // If we're not accessing anything in this constant, the result is undefined. if (uint64_t(Offset) >= TD.getTypeAllocSize(GV->getInitializer()->getType())) return UndefValue::get(IntType); unsigned char RawBytes[32] = {0}; if (!ReadDataFromGlobal(GV->getInitializer(), Offset, RawBytes, BytesLoaded, TD)) return 0; APInt ResultVal = APInt(IntType->getBitWidth(), RawBytes[BytesLoaded-1]); for (unsigned i = 1; i != BytesLoaded; ++i) { ResultVal <<= 8; ResultVal |= RawBytes[BytesLoaded-1-i]; } return ConstantInt::get(IntType->getContext(), ResultVal); } /// ConstantFoldLoadFromConstPtr - Return the value that a load from C would /// produce if it is constant and determinable. If this is not determinable, /// return null. Constant *llvm::ConstantFoldLoadFromConstPtr(Constant *C, const TargetData *TD) { // First, try the easy cases: if (GlobalVariable *GV = dyn_cast(C)) if (GV->isConstant() && GV->hasDefinitiveInitializer()) return GV->getInitializer(); // If the loaded value isn't a constant expr, we can't handle it. ConstantExpr *CE = dyn_cast(C); if (!CE) return 0; if (CE->getOpcode() == Instruction::GetElementPtr) { if (GlobalVariable *GV = dyn_cast(CE->getOperand(0))) if (GV->isConstant() && GV->hasDefinitiveInitializer()) if (Constant *V = ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE)) return V; } // Instead of loading constant c string, use corresponding integer value // directly if string length is small enough. std::string Str; if (TD && GetConstantStringInfo(CE, Str) && !Str.empty()) { unsigned StrLen = Str.length(); const Type *Ty = cast(CE->getType())->getElementType(); unsigned NumBits = Ty->getPrimitiveSizeInBits(); // Replace load with immediate integer if the result is an integer or fp // value. if ((NumBits >> 3) == StrLen + 1 && (NumBits & 7) == 0 && (isa(Ty) || Ty->isFloatingPointTy())) { APInt StrVal(NumBits, 0); APInt SingleChar(NumBits, 0); if (TD->isLittleEndian()) { for (signed i = StrLen-1; i >= 0; i--) { SingleChar = (uint64_t) Str[i] & UCHAR_MAX; StrVal = (StrVal << 8) | SingleChar; } } else { for (unsigned i = 0; i < StrLen; i++) { SingleChar = (uint64_t) Str[i] & UCHAR_MAX; StrVal = (StrVal << 8) | SingleChar; } // Append NULL at the end. SingleChar = 0; StrVal = (StrVal << 8) | SingleChar; } Constant *Res = ConstantInt::get(CE->getContext(), StrVal); if (Ty->isFloatingPointTy()) Res = ConstantExpr::getBitCast(Res, Ty); return Res; } } // If this load comes from anywhere in a constant global, and if the global // is all undef or zero, we know what it loads. if (GlobalVariable *GV = dyn_cast(GetUnderlyingObject(CE))){ if (GV->isConstant() && GV->hasDefinitiveInitializer()) { const Type *ResTy = cast(C->getType())->getElementType(); if (GV->getInitializer()->isNullValue()) return Constant::getNullValue(ResTy); if (isa(GV->getInitializer())) return UndefValue::get(ResTy); } } // Try hard to fold loads from bitcasted strange and non-type-safe things. We // currently don't do any of this for big endian systems. It can be // generalized in the future if someone is interested. if (TD && TD->isLittleEndian()) return FoldReinterpretLoadFromConstPtr(CE, *TD); return 0; } static Constant *ConstantFoldLoadInst(const LoadInst *LI, const TargetData *TD){ if (LI->isVolatile()) return 0; if (Constant *C = dyn_cast(LI->getOperand(0))) return ConstantFoldLoadFromConstPtr(C, TD); return 0; } /// 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); } } return 0; } /// CastGEPIndices - If array indices are not pointer-sized integers, /// explicitly cast them so that they aren't implicitly casted by the /// getelementptr. static Constant *CastGEPIndices(Constant *const *Ops, unsigned NumOps, const Type *ResultTy, const TargetData *TD) { if (!TD) return 0; const Type *IntPtrTy = TD->getIntPtrType(ResultTy->getContext()); bool Any = false; SmallVector NewIdxs; for (unsigned i = 1; i != NumOps; ++i) { if ((i == 1 || !isa(GetElementPtrInst::getIndexedType(Ops[0]->getType(), reinterpret_cast(Ops+1), i-1))) && Ops[i]->getType() != IntPtrTy) { Any = true; NewIdxs.push_back(ConstantExpr::getCast(CastInst::getCastOpcode(Ops[i], true, IntPtrTy, true), Ops[i], IntPtrTy)); } else NewIdxs.push_back(Ops[i]); } if (!Any) return 0; Constant *C = ConstantExpr::getGetElementPtr(Ops[0], &NewIdxs[0], NewIdxs.size()); if (ConstantExpr *CE = dyn_cast(C)) if (Constant *Folded = ConstantFoldConstantExpression(CE, TD)) C = Folded; return C; } /// SymbolicallyEvaluateGEP - If we can symbolically evaluate the specified GEP /// constant expression, do so. static Constant *SymbolicallyEvaluateGEP(Constant *const *Ops, unsigned NumOps, const Type *ResultTy, const TargetData *TD) { Constant *Ptr = Ops[0]; if (!TD || !cast(Ptr->getType())->getElementType()->isSized()) return 0; unsigned BitWidth = TD->getTypeSizeInBits(TD->getIntPtrType(Ptr->getContext())); // 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' for (unsigned i = 1; i != NumOps; ++i) if (!isa(Ops[i])) return 0; APInt Offset = APInt(BitWidth, TD->getIndexedOffset(Ptr->getType(), (Value**)Ops+1, NumOps-1)); Ptr = cast(Ptr->stripPointerCasts()); // If this is a GEP of a GEP, fold it all into a single GEP. while (GEPOperator *GEP = dyn_cast(Ptr)) { SmallVector NestedOps(GEP->op_begin()+1, GEP->op_end()); // Do not try the incorporate the sub-GEP if some index is not a number. bool AllConstantInt = true; for (unsigned i = 0, e = NestedOps.size(); i != e; ++i) if (!isa(NestedOps[i])) { AllConstantInt = false; break; } if (!AllConstantInt) break; Ptr = cast(GEP->getOperand(0)); Offset += APInt(BitWidth, TD->getIndexedOffset(Ptr->getType(), (Value**)NestedOps.data(), NestedOps.size())); Ptr = cast(Ptr->stripPointerCasts()); } // If the base value for this address is a literal integer value, fold the // getelementptr to the resulting integer value casted to the pointer type. APInt BasePtr(BitWidth, 0); if (ConstantExpr *CE = dyn_cast(Ptr)) if (CE->getOpcode() == Instruction::IntToPtr) if (ConstantInt *Base = dyn_cast(CE->getOperand(0))) BasePtr = Base->getValue().zextOrTrunc(BitWidth); if (Ptr->isNullValue() || BasePtr != 0) { Constant *C = ConstantInt::get(Ptr->getContext(), Offset+BasePtr); return ConstantExpr::getIntToPtr(C, ResultTy); } // Otherwise form a regular getelementptr. Recompute the indices so that // we eliminate over-indexing of the notional static type array bounds. // This makes it easy to determine if the getelementptr is "inbounds". // Also, this helps GlobalOpt do SROA on GlobalVariables. const Type *Ty = Ptr->getType(); SmallVector NewIdxs; do { if (const SequentialType *ATy = dyn_cast(Ty)) { if (ATy->isPointerTy()) { // The only pointer indexing we'll do is on the first index of the GEP. if (!NewIdxs.empty()) break; // Only handle pointers to sized types, not pointers to functions. if (!ATy->getElementType()->isSized()) return 0; } // Determine which element of the array the offset points into. APInt ElemSize(BitWidth, TD->getTypeAllocSize(ATy->getElementType())); const IntegerType *IntPtrTy = TD->getIntPtrType(Ty->getContext()); if (ElemSize == 0) // The element size is 0. This may be [0 x Ty]*, so just use a zero // index for this level and proceed to the next level to see if it can // accommodate the offset. NewIdxs.push_back(ConstantInt::get(IntPtrTy, 0)); else { // The element size is non-zero divide the offset by the element // size (rounding down), to compute the index at this level. APInt NewIdx = Offset.udiv(ElemSize); Offset -= NewIdx * ElemSize; NewIdxs.push_back(ConstantInt::get(IntPtrTy, NewIdx)); } Ty = ATy->getElementType(); } else if (const StructType *STy = dyn_cast(Ty)) { // Determine which field of the struct the offset points into. The // getZExtValue is at least as safe as the StructLayout API because we // know the offset is within the struct at this point. const StructLayout &SL = *TD->getStructLayout(STy); unsigned ElIdx = SL.getElementContainingOffset(Offset.getZExtValue()); NewIdxs.push_back(ConstantInt::get(Type::getInt32Ty(Ty->getContext()), ElIdx)); Offset -= APInt(BitWidth, SL.getElementOffset(ElIdx)); Ty = STy->getTypeAtIndex(ElIdx); } else { // We've reached some non-indexable type. break; } } while (Ty != cast(ResultTy)->getElementType()); // If we haven't used up the entire offset by descending the static // type, then the offset is pointing into the middle of an indivisible // member, so we can't simplify it. if (Offset != 0) return 0; // Create a GEP. Constant *C = ConstantExpr::getGetElementPtr(Ptr, &NewIdxs[0], NewIdxs.size()); assert(cast(C->getType())->getElementType() == Ty && "Computed GetElementPtr has unexpected type!"); // If we ended up indexing a member with a type that doesn't match // the type of what the original indices indexed, add a cast. if (Ty != cast(ResultTy)->getElementType()) C = FoldBitCast(C, ResultTy, *TD); return C; } //===----------------------------------------------------------------------===// // Constant Folding public APIs //===----------------------------------------------------------------------===// /// ConstantFoldInstruction - Try to constant fold the specified instruction. /// If successful, the constant result is returned, if not, null is returned. /// Note that this fails if not all of the operands are constant. Otherwise, /// 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) { // Handle PHI nodes quickly here... if (PHINode *PN = dyn_cast(I)) { Constant *CommonValue = 0; for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { Value *Incoming = PN->getIncomingValue(i); // If the incoming value is undef then skip it. Note that while we could // skip the value if it is equal to the phi node itself we choose not to // because that would break the rule that constant folding only applies if // all operands are constants. if (isa(Incoming)) continue; // If the incoming value is not a constant, or is a different constant to // the one we saw previously, then give up. Constant *C = dyn_cast(Incoming); if (!C || (CommonValue && C != CommonValue)) return 0; CommonValue = C; } // If we reach here, all incoming values are the same constant or undef. return CommonValue ? CommonValue : UndefValue::get(PN->getType()); } // Scan the operand list, checking to see if they are all constants, if so, // hand off to ConstantFoldInstOperands. SmallVector Ops; for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) if (Constant *Op = dyn_cast(*i)) Ops.push_back(Op); else return 0; // All operands not constant! if (const CmpInst *CI = dyn_cast(I)) return ConstantFoldCompareInstOperands(CI->getPredicate(), Ops[0], Ops[1], TD); if (const LoadInst *LI = dyn_cast(I)) return ConstantFoldLoadInst(LI, TD); if (InsertValueInst *IVI = dyn_cast(I)) return ConstantExpr::getInsertValue( cast(IVI->getAggregateOperand()), cast(IVI->getInsertedValueOperand()), IVI->idx_begin(), IVI->getNumIndices()); if (ExtractValueInst *EVI = dyn_cast(I)) return ConstantExpr::getExtractValue( cast(EVI->getAggregateOperand()), EVI->idx_begin(), EVI->getNumIndices()); return ConstantFoldInstOperands(I->getOpcode(), I->getType(), Ops.data(), Ops.size(), TD); } /// ConstantFoldConstantExpression - Attempt to fold the constant expression /// using the specified TargetData. If successful, the constant result is /// result is returned, if not, null is returned. Constant *llvm::ConstantFoldConstantExpression(const ConstantExpr *CE, const TargetData *TD) { SmallVector Ops; for (User::const_op_iterator i = CE->op_begin(), e = CE->op_end(); i != e; ++i) { Constant *NewC = cast(*i); // Recursively fold the ConstantExpr's operands. if (ConstantExpr *NewCE = dyn_cast(NewC)) NewC = ConstantFoldConstantExpression(NewCE, TD); Ops.push_back(NewC); } if (CE->isCompare()) return ConstantFoldCompareInstOperands(CE->getPredicate(), Ops[0], Ops[1], TD); return ConstantFoldInstOperands(CE->getOpcode(), CE->getType(), Ops.data(), 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. /// /// TODO: This function neither utilizes nor preserves nsw/nuw/inbounds/etc /// information, due to only being passed an opcode and operands. Constant /// folding using this function strips this information. /// Constant *llvm::ConstantFoldInstOperands(unsigned Opcode, const Type *DestTy, Constant* const* Ops, unsigned NumOps, const TargetData *TD) { // Handle easy binops first. if (Instruction::isBinaryOp(Opcode)) { if (isa(Ops[0]) || isa(Ops[1])) if (Constant *C = SymbolicallyEvaluateBinop(Opcode, Ops[0], Ops[1], TD)) return C; return ConstantExpr::get(Opcode, Ops[0], Ops[1]); } switch (Opcode) { default: return 0; case Instruction::ICmp: case Instruction::FCmp: assert(0 && "Invalid for compares"); case Instruction::Call: if (Function *F = dyn_cast(Ops[NumOps - 1])) if (canConstantFoldCallTo(F)) return ConstantFoldCall(F, Ops, NumOps - 1); return 0; 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(Ops[0])) { if (TD && CE->getOpcode() == Instruction::IntToPtr) { Constant *Input = CE->getOperand(0); unsigned InWidth = Input->getType()->getScalarSizeInBits(); if (TD->getPointerSizeInBits() < InWidth) { Constant *Mask = ConstantInt::get(CE->getContext(), 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, DestTy, false); } } return ConstantExpr::getCast(Opcode, Ops[0], DestTy); case Instruction::IntToPtr: // If the input is a ptrtoint, turn the pair into a ptr to ptr bitcast if // the int size is >= the ptr size. This requires knowing the width of a // pointer, so it can't be done in ConstantExpr::getCast. if (ConstantExpr *CE = dyn_cast(Ops[0])) if (TD && TD->getPointerSizeInBits() <= CE->getType()->getScalarSizeInBits() && CE->getOpcode() == Instruction::PtrToInt) return FoldBitCast(CE->getOperand(0), DestTy, *TD); return ConstantExpr::getCast(Opcode, Ops[0], DestTy); 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: return ConstantExpr::getCast(Opcode, Ops[0], DestTy); case Instruction::BitCast: if (TD) return FoldBitCast(Ops[0], DestTy, *TD); return ConstantExpr::getBitCast(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 = CastGEPIndices(Ops, NumOps, DestTy, TD)) return C; if (Constant *C = SymbolicallyEvaluateGEP(Ops, NumOps, DestTy, TD)) return C; return ConstantExpr::getGetElementPtr(Ops[0], Ops+1, NumOps-1); } } /// ConstantFoldCompareInstOperands - Attempt to constant fold a compare /// instruction (icmp/fcmp) with the specified operands. If it fails, it /// returns a constant expression of the specified operands. /// Constant *llvm::ConstantFoldCompareInstOperands(unsigned Predicate, Constant *Ops0, Constant *Ops1, const TargetData *TD) { // fold: icmp (inttoptr x), null -> icmp x, 0 // fold: icmp (ptrtoint x), 0 -> icmp x, null // fold: icmp (inttoptr x), (inttoptr y) -> icmp trunc/zext x, trunc/zext y // fold: icmp (ptrtoint x), (ptrtoint y) -> icmp x, y // // ConstantExpr::getCompare cannot do this, because it doesn't have TD // around to know if bit truncation is happening. if (ConstantExpr *CE0 = dyn_cast(Ops0)) { if (TD && Ops1->isNullValue()) { const Type *IntPtrTy = TD->getIntPtrType(CE0->getContext()); if (CE0->getOpcode() == Instruction::IntToPtr) { // Convert the integer value to the right size to ensure we get the // proper extension or truncation. Constant *C = ConstantExpr::getIntegerCast(CE0->getOperand(0), IntPtrTy, false); Constant *Null = Constant::getNullValue(C->getType()); return ConstantFoldCompareInstOperands(Predicate, C, Null, TD); } // Only do this transformation if the int is intptrty in size, otherwise // there is a truncation or extension that we aren't modeling. if (CE0->getOpcode() == Instruction::PtrToInt && CE0->getType() == IntPtrTy) { Constant *C = CE0->getOperand(0); Constant *Null = Constant::getNullValue(C->getType()); return ConstantFoldCompareInstOperands(Predicate, C, Null, TD); } } if (ConstantExpr *CE1 = dyn_cast(Ops1)) { if (TD && CE0->getOpcode() == CE1->getOpcode()) { const Type *IntPtrTy = TD->getIntPtrType(CE0->getContext()); if (CE0->getOpcode() == Instruction::IntToPtr) { // Convert the integer value to the right size to ensure we get the // proper extension or truncation. Constant *C0 = ConstantExpr::getIntegerCast(CE0->getOperand(0), IntPtrTy, false); Constant *C1 = ConstantExpr::getIntegerCast(CE1->getOperand(0), IntPtrTy, false); return ConstantFoldCompareInstOperands(Predicate, C0, C1, TD); } // Only do this transformation if the int is intptrty in size, otherwise // there is a truncation or extension that we aren't modeling. if ((CE0->getOpcode() == Instruction::PtrToInt && CE0->getType() == IntPtrTy && CE0->getOperand(0)->getType() == CE1->getOperand(0)->getType())) return ConstantFoldCompareInstOperands(Predicate, CE0->getOperand(0), CE1->getOperand(0), TD); } } // icmp eq (or x, y), 0 -> (icmp eq x, 0) & (icmp eq y, 0) // icmp ne (or x, y), 0 -> (icmp ne x, 0) | (icmp ne y, 0) if ((Predicate == ICmpInst::ICMP_EQ || Predicate == ICmpInst::ICMP_NE) && CE0->getOpcode() == Instruction::Or && Ops1->isNullValue()) { Constant *LHS = ConstantFoldCompareInstOperands(Predicate, CE0->getOperand(0), Ops1,TD); Constant *RHS = ConstantFoldCompareInstOperands(Predicate, CE0->getOperand(1), Ops1,TD); unsigned OpC = Predicate == ICmpInst::ICMP_EQ ? Instruction::And : Instruction::Or; Constant *Ops[] = { LHS, RHS }; return ConstantFoldInstOperands(OpC, LHS->getType(), Ops, 2, TD); } } return ConstantExpr::getCompare(Predicate, Ops0, Ops1); } /// 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(*I)) { ConstantInt *CU = cast(I.getOperand()); assert(CU->getZExtValue() < STy->getNumElements() && "Struct index out of range!"); unsigned El = (unsigned)CU->getZExtValue(); if (ConstantStruct *CS = dyn_cast(C)) { C = CS->getOperand(El); } else if (isa(C)) { C = Constant::getNullValue(STy->getElementType(El)); } else if (isa(C)) { C = UndefValue::get(STy->getElementType(El)); } else { return 0; } } else if (ConstantInt *CI = dyn_cast(I.getOperand())) { if (const ArrayType *ATy = dyn_cast(*I)) { if (CI->getZExtValue() >= ATy->getNumElements()) return 0; if (ConstantArray *CA = dyn_cast(C)) C = CA->getOperand(CI->getZExtValue()); else if (isa(C)) C = Constant::getNullValue(ATy->getElementType()); else if (isa(C)) C = UndefValue::get(ATy->getElementType()); else return 0; } else if (const VectorType *VTy = dyn_cast(*I)) { if (CI->getZExtValue() >= VTy->getNumElements()) return 0; if (ConstantVector *CP = dyn_cast(C)) C = CP->getOperand(CI->getZExtValue()); else if (isa(C)) C = Constant::getNullValue(VTy->getElementType()); else if (isa(C)) C = UndefValue::get(VTy->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(const Function *F) { switch (F->getIntrinsicID()) { case Intrinsic::sqrt: case Intrinsic::powi: case Intrinsic::bswap: case Intrinsic::ctpop: case Intrinsic::ctlz: case Intrinsic::cttz: case Intrinsic::uadd_with_overflow: case Intrinsic::usub_with_overflow: case Intrinsic::sadd_with_overflow: case Intrinsic::ssub_with_overflow: case Intrinsic::smul_with_overflow: case Intrinsic::convert_from_fp16: case Intrinsic::convert_to_fp16: return true; default: return false; case 0: break; } if (!F->hasName()) return false; StringRef Name = F->getName(); // 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 (Name[0]) { default: return false; case 'a': return Name == "acos" || Name == "asin" || Name == "atan" || Name == "atan2"; case 'c': return Name == "cos" || Name == "ceil" || Name == "cosf" || Name == "cosh"; case 'e': return Name == "exp"; case 'f': return Name == "fabs" || Name == "fmod" || Name == "floor"; case 'l': return Name == "log" || Name == "log10"; case 'p': return Name == "pow"; case 's': return Name == "sin" || Name == "sinh" || Name == "sqrt" || Name == "sinf" || Name == "sqrtf"; case 't': return Name == "tan" || Name == "tanh"; } } static Constant *ConstantFoldFP(double (*NativeFP)(double), double V, const Type *Ty) { sys::llvm_fenv_clearexcept(); V = NativeFP(V); if (sys::llvm_fenv_testexcept()) { sys::llvm_fenv_clearexcept(); return 0; } if (Ty->isFloatTy()) return ConstantFP::get(Ty->getContext(), APFloat((float)V)); if (Ty->isDoubleTy()) return ConstantFP::get(Ty->getContext(), APFloat(V)); llvm_unreachable("Can only constant fold float/double"); return 0; // dummy return to suppress warning } static Constant *ConstantFoldBinaryFP(double (*NativeFP)(double, double), double V, double W, const Type *Ty) { sys::llvm_fenv_clearexcept(); V = NativeFP(V, W); if (sys::llvm_fenv_testexcept()) { sys::llvm_fenv_clearexcept(); return 0; } if (Ty->isFloatTy()) return ConstantFP::get(Ty->getContext(), APFloat((float)V)); if (Ty->isDoubleTy()) return ConstantFP::get(Ty->getContext(), APFloat(V)); llvm_unreachable("Can only constant fold float/double"); return 0; // dummy return to suppress warning } /// 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 *const *Operands, unsigned NumOperands) { if (!F->hasName()) return 0; StringRef Name = F->getName(); const Type *Ty = F->getReturnType(); if (NumOperands == 1) { if (ConstantFP *Op = dyn_cast(Operands[0])) { if (Name == "llvm.convert.to.fp16") { APFloat Val(Op->getValueAPF()); bool lost = false; Val.convert(APFloat::IEEEhalf, APFloat::rmNearestTiesToEven, &lost); return ConstantInt::get(F->getContext(), Val.bitcastToAPInt()); } if (!Ty->isFloatTy() && !Ty->isDoubleTy()) return 0; /// We only fold functions with finite arguments. Folding NaN and inf is /// likely to be aborted with an exception anyway, and some host libms /// have known errors raising exceptions. if (Op->getValueAPF().isNaN() || Op->getValueAPF().isInfinity()) 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->isFloatTy() ? (double)Op->getValueAPF().convertToFloat() : Op->getValueAPF().convertToDouble(); switch (Name[0]) { case 'a': if (Name == "acos") return ConstantFoldFP(acos, V, Ty); else if (Name == "asin") return ConstantFoldFP(asin, V, Ty); else if (Name == "atan") return ConstantFoldFP(atan, V, Ty); break; case 'c': if (Name == "ceil") return ConstantFoldFP(ceil, V, Ty); else if (Name == "cos") return ConstantFoldFP(cos, V, Ty); else if (Name == "cosh") return ConstantFoldFP(cosh, V, Ty); else if (Name == "cosf") return ConstantFoldFP(cos, V, Ty); break; case 'e': if (Name == "exp") return ConstantFoldFP(exp, V, Ty); break; case 'f': if (Name == "fabs") return ConstantFoldFP(fabs, V, Ty); else if (Name == "floor") return ConstantFoldFP(floor, V, Ty); break; case 'l': if (Name == "log" && V > 0) return ConstantFoldFP(log, V, Ty); else if (Name == "log10" && V > 0) return ConstantFoldFP(log10, V, Ty); else if (Name == "llvm.sqrt.f32" || Name == "llvm.sqrt.f64") { if (V >= -0.0) return ConstantFoldFP(sqrt, V, Ty); else // Undefined return Constant::getNullValue(Ty); } break; case 's': if (Name == "sin") return ConstantFoldFP(sin, V, Ty); else if (Name == "sinh") return ConstantFoldFP(sinh, V, Ty); else if (Name == "sqrt" && V >= 0) return ConstantFoldFP(sqrt, V, Ty); else if (Name == "sqrtf" && V >= 0) return ConstantFoldFP(sqrt, V, Ty); else if (Name == "sinf") return ConstantFoldFP(sin, V, Ty); break; case 't': if (Name == "tan") return ConstantFoldFP(tan, V, Ty); else if (Name == "tanh") return ConstantFoldFP(tanh, V, Ty); break; default: break; } return 0; } if (ConstantInt *Op = dyn_cast(Operands[0])) { if (Name.startswith("llvm.bswap")) return ConstantInt::get(F->getContext(), Op->getValue().byteSwap()); else if (Name.startswith("llvm.ctpop")) return ConstantInt::get(Ty, Op->getValue().countPopulation()); else if (Name.startswith("llvm.cttz")) return ConstantInt::get(Ty, Op->getValue().countTrailingZeros()); else if (Name.startswith("llvm.ctlz")) return ConstantInt::get(Ty, Op->getValue().countLeadingZeros()); else if (Name == "llvm.convert.from.fp16") { APFloat Val(Op->getValue()); bool lost = false; APFloat::opStatus status = Val.convert(APFloat::IEEEsingle, APFloat::rmNearestTiesToEven, &lost); // Conversion is always precise. status = status; assert(status == APFloat::opOK && !lost && "Precision lost during fp16 constfolding"); return ConstantFP::get(F->getContext(), Val); } return 0; } if (isa(Operands[0])) { if (Name.startswith("llvm.bswap")) return Operands[0]; return 0; } return 0; } if (NumOperands == 2) { if (ConstantFP *Op1 = dyn_cast(Operands[0])) { if (!Ty->isFloatTy() && !Ty->isDoubleTy()) return 0; double Op1V = Ty->isFloatTy() ? (double)Op1->getValueAPF().convertToFloat() : Op1->getValueAPF().convertToDouble(); if (ConstantFP *Op2 = dyn_cast(Operands[1])) { if (Op2->getType() != Op1->getType()) return 0; double Op2V = Ty->isFloatTy() ? (double)Op2->getValueAPF().convertToFloat(): Op2->getValueAPF().convertToDouble(); if (Name == "pow") return ConstantFoldBinaryFP(pow, Op1V, Op2V, Ty); if (Name == "fmod") return ConstantFoldBinaryFP(fmod, Op1V, Op2V, Ty); if (Name == "atan2") return ConstantFoldBinaryFP(atan2, Op1V, Op2V, Ty); } else if (ConstantInt *Op2C = dyn_cast(Operands[1])) { if (Name == "llvm.powi.f32") return ConstantFP::get(F->getContext(), APFloat((float)std::pow((float)Op1V, (int)Op2C->getZExtValue()))); if (Name == "llvm.powi.f64") return ConstantFP::get(F->getContext(), APFloat((double)std::pow((double)Op1V, (int)Op2C->getZExtValue()))); } return 0; } if (ConstantInt *Op1 = dyn_cast(Operands[0])) { if (ConstantInt *Op2 = dyn_cast(Operands[1])) { switch (F->getIntrinsicID()) { default: break; case Intrinsic::sadd_with_overflow: case Intrinsic::uadd_with_overflow: case Intrinsic::ssub_with_overflow: case Intrinsic::usub_with_overflow: case Intrinsic::smul_with_overflow: { APInt Res; bool Overflow; switch (F->getIntrinsicID()) { default: assert(0 && "Invalid case"); case Intrinsic::sadd_with_overflow: Res = Op1->getValue().sadd_ov(Op2->getValue(), Overflow); break; case Intrinsic::uadd_with_overflow: Res = Op1->getValue().uadd_ov(Op2->getValue(), Overflow); break; case Intrinsic::ssub_with_overflow: Res = Op1->getValue().ssub_ov(Op2->getValue(), Overflow); break; case Intrinsic::usub_with_overflow: Res = Op1->getValue().usub_ov(Op2->getValue(), Overflow); break; case Intrinsic::smul_with_overflow: Res = Op1->getValue().smul_ov(Op2->getValue(), Overflow); break; } Constant *Ops[] = { ConstantInt::get(F->getContext(), Res), ConstantInt::get(Type::getInt1Ty(F->getContext()), Overflow) }; return ConstantStruct::get(F->getContext(), Ops, 2, false); } } } return 0; } return 0; } return 0; }