1 //===- AggressiveInstCombineInternal.h --------------------------*- 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 implements the instruction pattern combiner classes. 10 // Currently, it handles pattern expressions for: 11 // * Truncate instruction 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_LIB_TRANSFORMS_AGGRESSIVEINSTCOMBINE_COMBINEINTERNAL_H 16 #define LLVM_LIB_TRANSFORMS_AGGRESSIVEINSTCOMBINE_COMBINEINTERNAL_H 17 18 #include "llvm/ADT/MapVector.h" 19 #include "llvm/ADT/SmallVector.h" 20 21 using namespace llvm; 22 23 //===----------------------------------------------------------------------===// 24 // TruncInstCombine - looks for expression dags dominated by trunc instructions 25 // and for each eligible dag, it will create a reduced bit-width expression and 26 // replace the old expression with this new one and remove the old one. 27 // Eligible expression dag is such that: 28 // 1. Contains only supported instructions. 29 // 2. Supported leaves: ZExtInst, SExtInst, TruncInst and Constant value. 30 // 3. Can be evaluated into type with reduced legal bit-width (or Trunc type). 31 // 4. All instructions in the dag must not have users outside the dag. 32 // Only exception is for {ZExt, SExt}Inst with operand type equal to the 33 // new reduced type chosen in (3). 34 // 35 // The motivation for this optimization is that evaluating and expression using 36 // smaller bit-width is preferable, especially for vectorization where we can 37 // fit more values in one vectorized instruction. In addition, this optimization 38 // may decrease the number of cast instructions, but will not increase it. 39 //===----------------------------------------------------------------------===// 40 41 namespace llvm { 42 class DataLayout; 43 class DominatorTree; 44 class Function; 45 class Instruction; 46 class TargetLibraryInfo; 47 class TruncInst; 48 class Type; 49 class Value; 50 51 class TruncInstCombine { 52 TargetLibraryInfo &TLI; 53 const DataLayout &DL; 54 const DominatorTree &DT; 55 56 /// List of all TruncInst instructions to be processed. 57 SmallVector<TruncInst *, 4> Worklist; 58 59 /// Current processed TruncInst instruction. 60 TruncInst *CurrentTruncInst; 61 62 /// Information per each instruction in the expression dag. 63 struct Info { 64 /// Number of LSBs that are needed to generate a valid expression. 65 unsigned ValidBitWidth = 0; 66 /// Minimum number of LSBs needed to generate the ValidBitWidth. 67 unsigned MinBitWidth = 0; 68 /// The reduced value generated to replace the old instruction. 69 Value *NewValue = nullptr; 70 }; 71 /// An ordered map representing expression dag post-dominated by current 72 /// processed TruncInst. It maps each instruction in the dag to its Info 73 /// structure. The map is ordered such that each instruction appears before 74 /// all other instructions in the dag that uses it. 75 MapVector<Instruction *, Info> InstInfoMap; 76 77 public: 78 TruncInstCombine(TargetLibraryInfo &TLI, const DataLayout &DL, 79 const DominatorTree &DT) 80 : TLI(TLI), DL(DL), DT(DT), CurrentTruncInst(nullptr) {} 81 82 /// Perform TruncInst pattern optimization on given function. 83 bool run(Function &F); 84 85 private: 86 /// Build expression dag dominated by the /p CurrentTruncInst and append it to 87 /// the InstInfoMap container. 88 /// 89 /// \return true only if succeed to generate an eligible sub expression dag. 90 bool buildTruncExpressionDag(); 91 92 /// Calculate the minimal allowed bit-width of the chain ending with the 93 /// currently visited truncate's operand. 94 /// 95 /// \return minimum number of bits to which the chain ending with the 96 /// truncate's operand can be shrunk to. 97 unsigned getMinBitWidth(); 98 99 /// Build an expression dag dominated by the current processed TruncInst and 100 /// Check if it is eligible to be reduced to a smaller type. 101 /// 102 /// \return the scalar version of the new type to be used for the reduced 103 /// expression dag, or nullptr if the expression dag is not eligible 104 /// to be reduced. 105 Type *getBestTruncatedType(); 106 107 /// Given a \p V value and a \p SclTy scalar type return the generated reduced 108 /// value of \p V based on the type \p SclTy. 109 /// 110 /// \param V value to be reduced. 111 /// \param SclTy scalar version of new type to reduce to. 112 /// \return the new reduced value. 113 Value *getReducedOperand(Value *V, Type *SclTy); 114 115 /// Create a new expression dag using the reduced /p SclTy type and replace 116 /// the old expression dag with it. Also erase all instructions in the old 117 /// dag, except those that are still needed outside the dag. 118 /// 119 /// \param SclTy scalar version of new type to reduce expression dag into. 120 void ReduceExpressionDag(Type *SclTy); 121 }; 122 } // end namespace llvm. 123 124 #endif 125