1 //===-- ConstantFolding.h - Fold instructions into constants ----*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file declares routines for folding instructions into constants when all 10 // operands are constants, for example "sub i32 1, 0" -> "1". 11 // 12 // Also, to supplement the basic VMCore ConstantExpr simplifications, 13 // this file declares some additional folding routines that can make use of 14 // DataLayout information. These functions cannot go in VMCore due to library 15 // dependency issues. 16 // 17 //===----------------------------------------------------------------------===// 18 19 #ifndef LLVM_ANALYSIS_CONSTANTFOLDING_H 20 #define LLVM_ANALYSIS_CONSTANTFOLDING_H 21 22 #include <stdint.h> 23 24 namespace llvm { 25 26 namespace Intrinsic { 27 using ID = unsigned; 28 } 29 30 class APInt; 31 template <typename T> class ArrayRef; 32 class CallBase; 33 class Constant; 34 class DSOLocalEquivalent; 35 class DataLayout; 36 class Function; 37 class GlobalValue; 38 class GlobalVariable; 39 class Instruction; 40 class TargetLibraryInfo; 41 class Type; 42 43 /// If this constant is a constant offset from a global, return the global and 44 /// the constant. Because of constantexprs, this function is recursive. 45 /// If the global is part of a dso_local_equivalent constant, return it through 46 /// `Equiv` if it is provided. 47 bool IsConstantOffsetFromGlobal(Constant *C, GlobalValue *&GV, APInt &Offset, 48 const DataLayout &DL, 49 DSOLocalEquivalent **DSOEquiv = nullptr); 50 51 /// ConstantFoldInstruction - Try to constant fold the specified instruction. 52 /// If successful, the constant result is returned, if not, null is returned. 53 /// Note that this fails if not all of the operands are constant. Otherwise, 54 /// this function can only fail when attempting to fold instructions like loads 55 /// and stores, which have no constant expression form. 56 Constant *ConstantFoldInstruction(Instruction *I, const DataLayout &DL, 57 const TargetLibraryInfo *TLI = nullptr); 58 59 /// ConstantFoldConstant - Fold the constant using the specified DataLayout. 60 /// This function always returns a non-null constant: Either the folding result, 61 /// or the original constant if further folding is not possible. 62 Constant *ConstantFoldConstant(const Constant *C, const DataLayout &DL, 63 const TargetLibraryInfo *TLI = nullptr); 64 65 /// ConstantFoldInstOperands - Attempt to constant fold an instruction with the 66 /// specified operands. If successful, the constant result is returned, if not, 67 /// null is returned. Note that this function can fail when attempting to 68 /// fold instructions like loads and stores, which have no constant expression 69 /// form. 70 /// 71 /// In some cases, constant folding may return one value chosen from a set of 72 /// multiple legal return values. For example, the exact bit pattern of NaN 73 /// results is not guaranteed. Using such a result is usually only valid if 74 /// all uses of the original operation are replaced by the constant-folded 75 /// result. The \p AllowNonDeterministic parameter controls whether this is 76 /// allowed. 77 Constant *ConstantFoldInstOperands(Instruction *I, ArrayRef<Constant *> Ops, 78 const DataLayout &DL, 79 const TargetLibraryInfo *TLI = nullptr, 80 bool AllowNonDeterministic = true); 81 82 /// Attempt to constant fold a compare instruction (icmp/fcmp) with the 83 /// specified operands. Returns null or a constant expression of the specified 84 /// operands on failure. 85 /// Denormal inputs may be flushed based on the denormal handling mode. 86 Constant *ConstantFoldCompareInstOperands( 87 unsigned Predicate, Constant *LHS, Constant *RHS, const DataLayout &DL, 88 const TargetLibraryInfo *TLI = nullptr, const Instruction *I = nullptr); 89 90 /// Attempt to constant fold a unary operation with the specified operand. 91 /// Returns null on failure. 92 Constant *ConstantFoldUnaryOpOperand(unsigned Opcode, Constant *Op, 93 const DataLayout &DL); 94 95 /// Attempt to constant fold a binary operation with the specified operands. 96 /// Returns null or a constant expression of the specified operands on failure. 97 Constant *ConstantFoldBinaryOpOperands(unsigned Opcode, Constant *LHS, 98 Constant *RHS, const DataLayout &DL); 99 100 /// Attempt to constant fold a floating point binary operation with the 101 /// specified operands, applying the denormal handling mod to the operands. 102 /// Returns null or a constant expression of the specified operands on failure. 103 Constant *ConstantFoldFPInstOperands(unsigned Opcode, Constant *LHS, 104 Constant *RHS, const DataLayout &DL, 105 const Instruction *I, 106 bool AllowNonDeterministic = true); 107 108 /// Attempt to flush float point constant according to denormal mode set in the 109 /// instruction's parent function attributes. If so, return a zero with the 110 /// correct sign, otherwise return the original constant. Inputs and outputs to 111 /// floating point instructions can have their mode set separately, so the 112 /// direction is also needed. 113 /// 114 /// If the calling function's "denormal-fp-math" input mode is "dynamic" for the 115 /// floating-point type, returns nullptr for denormal inputs. 116 Constant *FlushFPConstant(Constant *Operand, const Instruction *I, 117 bool IsOutput); 118 119 /// Attempt to constant fold a select instruction with the specified 120 /// operands. The constant result is returned if successful; if not, null is 121 /// returned. 122 Constant *ConstantFoldSelectInstruction(Constant *Cond, Constant *V1, 123 Constant *V2); 124 125 /// Attempt to constant fold a cast with the specified operand. If it 126 /// fails, it returns a constant expression of the specified operand. 127 Constant *ConstantFoldCastOperand(unsigned Opcode, Constant *C, Type *DestTy, 128 const DataLayout &DL); 129 130 /// Constant fold a zext, sext or trunc, depending on IsSigned and whether the 131 /// DestTy is wider or narrower than C. Returns nullptr on failure. 132 Constant *ConstantFoldIntegerCast(Constant *C, Type *DestTy, bool IsSigned, 133 const DataLayout &DL); 134 135 /// ConstantFoldInsertValueInstruction - Attempt to constant fold an insertvalue 136 /// instruction with the specified operands and indices. The constant result is 137 /// returned if successful; if not, null is returned. 138 Constant *ConstantFoldInsertValueInstruction(Constant *Agg, Constant *Val, 139 ArrayRef<unsigned> Idxs); 140 141 /// Attempt to constant fold an extractvalue instruction with the 142 /// specified operands and indices. The constant result is returned if 143 /// successful; if not, null is returned. 144 Constant *ConstantFoldExtractValueInstruction(Constant *Agg, 145 ArrayRef<unsigned> Idxs); 146 147 /// Attempt to constant fold an insertelement instruction with the 148 /// specified operands and indices. The constant result is returned if 149 /// successful; if not, null is returned. 150 Constant *ConstantFoldInsertElementInstruction(Constant *Val, 151 Constant *Elt, 152 Constant *Idx); 153 154 /// Attempt to constant fold an extractelement instruction with the 155 /// specified operands and indices. The constant result is returned if 156 /// successful; if not, null is returned. 157 Constant *ConstantFoldExtractElementInstruction(Constant *Val, Constant *Idx); 158 159 /// Attempt to constant fold a shufflevector instruction with the 160 /// specified operands and mask. See class ShuffleVectorInst for a description 161 /// of the mask representation. The constant result is returned if successful; 162 /// if not, null is returned. 163 Constant *ConstantFoldShuffleVectorInstruction(Constant *V1, Constant *V2, 164 ArrayRef<int> Mask); 165 166 /// Extract value of C at the given Offset reinterpreted as Ty. If bits past 167 /// the end of C are accessed, they are assumed to be poison. 168 Constant *ConstantFoldLoadFromConst(Constant *C, Type *Ty, const APInt &Offset, 169 const DataLayout &DL); 170 171 /// Extract value of C reinterpreted as Ty. Same as previous API with zero 172 /// offset. 173 Constant *ConstantFoldLoadFromConst(Constant *C, Type *Ty, 174 const DataLayout &DL); 175 176 /// Return the value that a load from C with offset Offset would produce if it 177 /// is constant and determinable. If this is not determinable, return null. 178 Constant *ConstantFoldLoadFromConstPtr(Constant *C, Type *Ty, APInt Offset, 179 const DataLayout &DL); 180 181 /// Return the value that a load from C would produce if it is constant and 182 /// determinable. If this is not determinable, return null. 183 Constant *ConstantFoldLoadFromConstPtr(Constant *C, Type *Ty, 184 const DataLayout &DL); 185 186 /// If C is a uniform value where all bits are the same (either all zero, all 187 /// ones, all undef or all poison), return the corresponding uniform value in 188 /// the new type. If the value is not uniform or the result cannot be 189 /// represented, return null. 190 Constant *ConstantFoldLoadFromUniformValue(Constant *C, Type *Ty, 191 const DataLayout &DL); 192 193 /// canConstantFoldCallTo - Return true if its even possible to fold a call to 194 /// the specified function. 195 bool canConstantFoldCallTo(const CallBase *Call, const Function *F); 196 197 /// ConstantFoldCall - Attempt to constant fold a call to the specified function 198 /// with the specified arguments, returning null if unsuccessful. 199 Constant *ConstantFoldCall(const CallBase *Call, Function *F, 200 ArrayRef<Constant *> Operands, 201 const TargetLibraryInfo *TLI = nullptr, 202 bool AllowNonDeterministic = true); 203 204 Constant *ConstantFoldBinaryIntrinsic(Intrinsic::ID ID, Constant *LHS, 205 Constant *RHS, Type *Ty, 206 Instruction *FMFSource); 207 208 /// ConstantFoldLoadThroughBitcast - try to cast constant to destination type 209 /// returning null if unsuccessful. Can cast pointer to pointer or pointer to 210 /// integer and vice versa if their sizes are equal. 211 Constant *ConstantFoldLoadThroughBitcast(Constant *C, Type *DestTy, 212 const DataLayout &DL); 213 214 /// Check whether the given call has no side-effects. 215 /// Specifically checks for math routimes which sometimes set errno. 216 bool isMathLibCallNoop(const CallBase *Call, const TargetLibraryInfo *TLI); 217 218 Constant *ReadByteArrayFromGlobal(const GlobalVariable *GV, uint64_t Offset); 219 } 220 221 #endif 222