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 class APInt; 26 template <typename T> class ArrayRef; 27 class CallBase; 28 class Constant; 29 class DSOLocalEquivalent; 30 class DataLayout; 31 class Function; 32 class GlobalValue; 33 class GlobalVariable; 34 class Instruction; 35 class TargetLibraryInfo; 36 class Type; 37 38 /// If this constant is a constant offset from a global, return the global and 39 /// the constant. Because of constantexprs, this function is recursive. 40 /// If the global is part of a dso_local_equivalent constant, return it through 41 /// `Equiv` if it is provided. 42 bool IsConstantOffsetFromGlobal(Constant *C, GlobalValue *&GV, APInt &Offset, 43 const DataLayout &DL, 44 DSOLocalEquivalent **DSOEquiv = nullptr); 45 46 /// ConstantFoldInstruction - Try to constant fold the specified instruction. 47 /// If successful, the constant result is returned, if not, null is returned. 48 /// Note that this fails if not all of the operands are constant. Otherwise, 49 /// this function can only fail when attempting to fold instructions like loads 50 /// and stores, which have no constant expression form. 51 Constant *ConstantFoldInstruction(Instruction *I, const DataLayout &DL, 52 const TargetLibraryInfo *TLI = nullptr); 53 54 /// ConstantFoldConstant - Fold the constant using the specified DataLayout. 55 /// This function always returns a non-null constant: Either the folding result, 56 /// or the original constant if further folding is not possible. 57 Constant *ConstantFoldConstant(const Constant *C, const DataLayout &DL, 58 const TargetLibraryInfo *TLI = nullptr); 59 60 /// ConstantFoldInstOperands - Attempt to constant fold an instruction with the 61 /// specified operands. If successful, the constant result is returned, if not, 62 /// null is returned. Note that this function can fail when attempting to 63 /// fold instructions like loads and stores, which have no constant expression 64 /// form. 65 /// 66 Constant *ConstantFoldInstOperands(Instruction *I, ArrayRef<Constant *> Ops, 67 const DataLayout &DL, 68 const TargetLibraryInfo *TLI = nullptr); 69 70 /// Attempt to constant fold a compare instruction (icmp/fcmp) with the 71 /// specified operands. Returns null or a constant expression of the specified 72 /// operands on failure. 73 /// Denormal inputs may be flushed based on the denormal handling mode. 74 Constant *ConstantFoldCompareInstOperands( 75 unsigned Predicate, Constant *LHS, Constant *RHS, const DataLayout &DL, 76 const TargetLibraryInfo *TLI = nullptr, const Instruction *I = nullptr); 77 78 /// Attempt to constant fold a unary operation with the specified operand. 79 /// Returns null on failure. 80 Constant *ConstantFoldUnaryOpOperand(unsigned Opcode, Constant *Op, 81 const DataLayout &DL); 82 83 /// Attempt to constant fold a binary operation with the specified operands. 84 /// Returns null or a constant expression of the specified operands on failure. 85 Constant *ConstantFoldBinaryOpOperands(unsigned Opcode, Constant *LHS, 86 Constant *RHS, const DataLayout &DL); 87 88 /// Attempt to constant fold a floating point binary operation with the 89 /// specified operands, applying the denormal handling mod to the operands. 90 /// Returns null or a constant expression of the specified operands on failure. 91 Constant *ConstantFoldFPInstOperands(unsigned Opcode, Constant *LHS, 92 Constant *RHS, const DataLayout &DL, 93 const Instruction *I); 94 95 /// Attempt to flush float point constant according to denormal mode set in the 96 /// instruction's parent function attributes. If so, return a zero with the 97 /// correct sign, otherwise return the original constant. Inputs and outputs to 98 /// floating point instructions can have their mode set separately, so the 99 /// direction is also needed. 100 /// 101 /// If the calling function's "denormal-fp-math" input mode is "dynamic" for the 102 /// floating-point type, returns nullptr for denormal inputs. 103 Constant *FlushFPConstant(Constant *Operand, const Instruction *I, 104 bool IsOutput); 105 106 /// Attempt to constant fold a select instruction with the specified 107 /// operands. The constant result is returned if successful; if not, null is 108 /// returned. 109 Constant *ConstantFoldSelectInstruction(Constant *Cond, Constant *V1, 110 Constant *V2); 111 112 /// Attempt to constant fold a cast with the specified operand. If it 113 /// fails, it returns a constant expression of the specified operand. 114 Constant *ConstantFoldCastOperand(unsigned Opcode, Constant *C, Type *DestTy, 115 const DataLayout &DL); 116 117 /// ConstantFoldInsertValueInstruction - Attempt to constant fold an insertvalue 118 /// instruction with the specified operands and indices. The constant result is 119 /// returned if successful; if not, null is returned. 120 Constant *ConstantFoldInsertValueInstruction(Constant *Agg, Constant *Val, 121 ArrayRef<unsigned> Idxs); 122 123 /// Attempt to constant fold an extractvalue instruction with the 124 /// specified operands and indices. The constant result is returned if 125 /// successful; if not, null is returned. 126 Constant *ConstantFoldExtractValueInstruction(Constant *Agg, 127 ArrayRef<unsigned> Idxs); 128 129 /// Attempt to constant fold an insertelement instruction with the 130 /// specified operands and indices. The constant result is returned if 131 /// successful; if not, null is returned. 132 Constant *ConstantFoldInsertElementInstruction(Constant *Val, 133 Constant *Elt, 134 Constant *Idx); 135 136 /// Attempt to constant fold an extractelement instruction with the 137 /// specified operands and indices. The constant result is returned if 138 /// successful; if not, null is returned. 139 Constant *ConstantFoldExtractElementInstruction(Constant *Val, Constant *Idx); 140 141 /// Attempt to constant fold a shufflevector instruction with the 142 /// specified operands and mask. See class ShuffleVectorInst for a description 143 /// of the mask representation. The constant result is returned if successful; 144 /// if not, null is returned. 145 Constant *ConstantFoldShuffleVectorInstruction(Constant *V1, Constant *V2, 146 ArrayRef<int> Mask); 147 148 /// Extract value of C at the given Offset reinterpreted as Ty. If bits past 149 /// the end of C are accessed, they are assumed to be poison. 150 Constant *ConstantFoldLoadFromConst(Constant *C, Type *Ty, const APInt &Offset, 151 const DataLayout &DL); 152 153 /// Extract value of C reinterpreted as Ty. Same as previous API with zero 154 /// offset. 155 Constant *ConstantFoldLoadFromConst(Constant *C, Type *Ty, 156 const DataLayout &DL); 157 158 /// Return the value that a load from C with offset Offset would produce if it 159 /// is constant and determinable. If this is not determinable, return null. 160 Constant *ConstantFoldLoadFromConstPtr(Constant *C, Type *Ty, APInt Offset, 161 const DataLayout &DL); 162 163 /// Return the value that a load from C would produce if it is constant and 164 /// determinable. If this is not determinable, return null. 165 Constant *ConstantFoldLoadFromConstPtr(Constant *C, Type *Ty, 166 const DataLayout &DL); 167 168 /// If C is a uniform value where all bits are the same (either all zero, all 169 /// ones, all undef or all poison), return the corresponding uniform value in 170 /// the new type. If the value is not uniform or the result cannot be 171 /// represented, return null. 172 Constant *ConstantFoldLoadFromUniformValue(Constant *C, Type *Ty); 173 174 /// canConstantFoldCallTo - Return true if its even possible to fold a call to 175 /// the specified function. 176 bool canConstantFoldCallTo(const CallBase *Call, const Function *F); 177 178 /// ConstantFoldCall - Attempt to constant fold a call to the specified function 179 /// with the specified arguments, returning null if unsuccessful. 180 Constant *ConstantFoldCall(const CallBase *Call, Function *F, 181 ArrayRef<Constant *> Operands, 182 const TargetLibraryInfo *TLI = nullptr); 183 184 /// ConstantFoldLoadThroughBitcast - try to cast constant to destination type 185 /// returning null if unsuccessful. Can cast pointer to pointer or pointer to 186 /// integer and vice versa if their sizes are equal. 187 Constant *ConstantFoldLoadThroughBitcast(Constant *C, Type *DestTy, 188 const DataLayout &DL); 189 190 /// Check whether the given call has no side-effects. 191 /// Specifically checks for math routimes which sometimes set errno. 192 bool isMathLibCallNoop(const CallBase *Call, const TargetLibraryInfo *TLI); 193 194 Constant *ReadByteArrayFromGlobal(const GlobalVariable *GV, uint64_t Offset); 195 } 196 197 #endif 198