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 Constant *ConstantFoldInstOperands(Instruction *I, ArrayRef<Constant *> Ops, 72 const DataLayout &DL, 73 const TargetLibraryInfo *TLI = nullptr); 74 75 /// Attempt to constant fold a compare instruction (icmp/fcmp) with the 76 /// specified operands. Returns null or a constant expression of the specified 77 /// operands on failure. 78 /// Denormal inputs may be flushed based on the denormal handling mode. 79 Constant *ConstantFoldCompareInstOperands( 80 unsigned Predicate, Constant *LHS, Constant *RHS, const DataLayout &DL, 81 const TargetLibraryInfo *TLI = nullptr, const Instruction *I = nullptr); 82 83 /// Attempt to constant fold a unary operation with the specified operand. 84 /// Returns null on failure. 85 Constant *ConstantFoldUnaryOpOperand(unsigned Opcode, Constant *Op, 86 const DataLayout &DL); 87 88 /// Attempt to constant fold a binary operation with the specified operands. 89 /// Returns null or a constant expression of the specified operands on failure. 90 Constant *ConstantFoldBinaryOpOperands(unsigned Opcode, Constant *LHS, 91 Constant *RHS, const DataLayout &DL); 92 93 /// Attempt to constant fold a floating point binary operation with the 94 /// specified operands, applying the denormal handling mod to the operands. 95 /// Returns null or a constant expression of the specified operands on failure. 96 Constant *ConstantFoldFPInstOperands(unsigned Opcode, Constant *LHS, 97 Constant *RHS, const DataLayout &DL, 98 const Instruction *I); 99 100 /// Attempt to flush float point constant according to denormal mode set in the 101 /// instruction's parent function attributes. If so, return a zero with the 102 /// correct sign, otherwise return the original constant. Inputs and outputs to 103 /// floating point instructions can have their mode set separately, so the 104 /// direction is also needed. 105 /// 106 /// If the calling function's "denormal-fp-math" input mode is "dynamic" for the 107 /// floating-point type, returns nullptr for denormal inputs. 108 Constant *FlushFPConstant(Constant *Operand, const Instruction *I, 109 bool IsOutput); 110 111 /// Attempt to constant fold a select instruction with the specified 112 /// operands. The constant result is returned if successful; if not, null is 113 /// returned. 114 Constant *ConstantFoldSelectInstruction(Constant *Cond, Constant *V1, 115 Constant *V2); 116 117 /// Attempt to constant fold a cast with the specified operand. If it 118 /// fails, it returns a constant expression of the specified operand. 119 Constant *ConstantFoldCastOperand(unsigned Opcode, Constant *C, Type *DestTy, 120 const DataLayout &DL); 121 122 /// Constant fold a zext, sext or trunc, depending on IsSigned and whether the 123 /// DestTy is wider or narrower than C. Returns nullptr on failure. 124 Constant *ConstantFoldIntegerCast(Constant *C, Type *DestTy, bool IsSigned, 125 const DataLayout &DL); 126 127 /// ConstantFoldInsertValueInstruction - Attempt to constant fold an insertvalue 128 /// instruction with the specified operands and indices. The constant result is 129 /// returned if successful; if not, null is returned. 130 Constant *ConstantFoldInsertValueInstruction(Constant *Agg, Constant *Val, 131 ArrayRef<unsigned> Idxs); 132 133 /// Attempt to constant fold an extractvalue instruction with the 134 /// specified operands and indices. The constant result is returned if 135 /// successful; if not, null is returned. 136 Constant *ConstantFoldExtractValueInstruction(Constant *Agg, 137 ArrayRef<unsigned> Idxs); 138 139 /// Attempt to constant fold an insertelement instruction with the 140 /// specified operands and indices. The constant result is returned if 141 /// successful; if not, null is returned. 142 Constant *ConstantFoldInsertElementInstruction(Constant *Val, 143 Constant *Elt, 144 Constant *Idx); 145 146 /// Attempt to constant fold an extractelement instruction with the 147 /// specified operands and indices. The constant result is returned if 148 /// successful; if not, null is returned. 149 Constant *ConstantFoldExtractElementInstruction(Constant *Val, Constant *Idx); 150 151 /// Attempt to constant fold a shufflevector instruction with the 152 /// specified operands and mask. See class ShuffleVectorInst for a description 153 /// of the mask representation. The constant result is returned if successful; 154 /// if not, null is returned. 155 Constant *ConstantFoldShuffleVectorInstruction(Constant *V1, Constant *V2, 156 ArrayRef<int> Mask); 157 158 /// Extract value of C at the given Offset reinterpreted as Ty. If bits past 159 /// the end of C are accessed, they are assumed to be poison. 160 Constant *ConstantFoldLoadFromConst(Constant *C, Type *Ty, const APInt &Offset, 161 const DataLayout &DL); 162 163 /// Extract value of C reinterpreted as Ty. Same as previous API with zero 164 /// offset. 165 Constant *ConstantFoldLoadFromConst(Constant *C, Type *Ty, 166 const DataLayout &DL); 167 168 /// Return the value that a load from C with offset Offset would produce if it 169 /// is constant and determinable. If this is not determinable, return null. 170 Constant *ConstantFoldLoadFromConstPtr(Constant *C, Type *Ty, APInt Offset, 171 const DataLayout &DL); 172 173 /// Return the value that a load from C would produce if it is constant and 174 /// determinable. If this is not determinable, return null. 175 Constant *ConstantFoldLoadFromConstPtr(Constant *C, Type *Ty, 176 const DataLayout &DL); 177 178 /// If C is a uniform value where all bits are the same (either all zero, all 179 /// ones, all undef or all poison), return the corresponding uniform value in 180 /// the new type. If the value is not uniform or the result cannot be 181 /// represented, return null. 182 Constant *ConstantFoldLoadFromUniformValue(Constant *C, Type *Ty, 183 const DataLayout &DL); 184 185 /// canConstantFoldCallTo - Return true if its even possible to fold a call to 186 /// the specified function. 187 bool canConstantFoldCallTo(const CallBase *Call, const Function *F); 188 189 /// ConstantFoldCall - Attempt to constant fold a call to the specified function 190 /// with the specified arguments, returning null if unsuccessful. 191 Constant *ConstantFoldCall(const CallBase *Call, Function *F, 192 ArrayRef<Constant *> Operands, 193 const TargetLibraryInfo *TLI = nullptr); 194 195 Constant *ConstantFoldBinaryIntrinsic(Intrinsic::ID ID, Constant *LHS, 196 Constant *RHS, Type *Ty, 197 Instruction *FMFSource); 198 199 /// ConstantFoldLoadThroughBitcast - try to cast constant to destination type 200 /// returning null if unsuccessful. Can cast pointer to pointer or pointer to 201 /// integer and vice versa if their sizes are equal. 202 Constant *ConstantFoldLoadThroughBitcast(Constant *C, Type *DestTy, 203 const DataLayout &DL); 204 205 /// Check whether the given call has no side-effects. 206 /// Specifically checks for math routimes which sometimes set errno. 207 bool isMathLibCallNoop(const CallBase *Call, const TargetLibraryInfo *TLI); 208 209 Constant *ReadByteArrayFromGlobal(const GlobalVariable *GV, uint64_t Offset); 210 } 211 212 #endif 213