1 //===- SSAUpdater.h - Unstructured SSA Update Tool --------------*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file declares the SSAUpdater class. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_TRANSFORMS_UTILS_SSAUPDATER_H 15 #define LLVM_TRANSFORMS_UTILS_SSAUPDATER_H 16 17 #include "llvm/ADT/ArrayRef.h" 18 #include "llvm/ADT/StringRef.h" 19 #include <string> 20 21 namespace llvm { 22 23 class BasicBlock; 24 class Instruction; 25 class LoadInst; 26 class PHINode; 27 template <typename T> class SmallVectorImpl; 28 template <typename T> class SSAUpdaterTraits; 29 class Type; 30 class Use; 31 class Value; 32 33 /// \brief Helper class for SSA formation on a set of values defined in 34 /// multiple blocks. 35 /// 36 /// This is used when code duplication or another unstructured 37 /// transformation wants to rewrite a set of uses of one value with uses of a 38 /// set of values. 39 class SSAUpdater { 40 friend class SSAUpdaterTraits<SSAUpdater>; 41 42 private: 43 /// This keeps track of which value to use on a per-block basis. When we 44 /// insert PHI nodes, we keep track of them here. 45 void *AV = nullptr; 46 47 /// ProtoType holds the type of the values being rewritten. 48 Type *ProtoType = nullptr; 49 50 /// PHI nodes are given a name based on ProtoName. 51 std::string ProtoName; 52 53 /// If this is non-null, the SSAUpdater adds all PHI nodes that it creates to 54 /// the vector. 55 SmallVectorImpl<PHINode *> *InsertedPHIs; 56 57 public: 58 /// If InsertedPHIs is specified, it will be filled 59 /// in with all PHI Nodes created by rewriting. 60 explicit SSAUpdater(SmallVectorImpl<PHINode *> *InsertedPHIs = nullptr); 61 SSAUpdater(const SSAUpdater &) = delete; 62 SSAUpdater &operator=(const SSAUpdater &) = delete; 63 ~SSAUpdater(); 64 65 /// \brief Reset this object to get ready for a new set of SSA updates with 66 /// type 'Ty'. 67 /// 68 /// PHI nodes get a name based on 'Name'. 69 void Initialize(Type *Ty, StringRef Name); 70 71 /// \brief Indicate that a rewritten value is available in the specified block 72 /// with the specified value. 73 void AddAvailableValue(BasicBlock *BB, Value *V); 74 75 /// \brief Return true if the SSAUpdater already has a value for the specified 76 /// block. 77 bool HasValueForBlock(BasicBlock *BB) const; 78 79 /// \brief Construct SSA form, materializing a value that is live at the end 80 /// of the specified block. 81 Value *GetValueAtEndOfBlock(BasicBlock *BB); 82 83 /// \brief Construct SSA form, materializing a value that is live in the 84 /// middle of the specified block. 85 /// 86 /// \c GetValueInMiddleOfBlock is the same as \c GetValueAtEndOfBlock except 87 /// in one important case: if there is a definition of the rewritten value 88 /// after the 'use' in BB. Consider code like this: 89 /// 90 /// \code 91 /// X1 = ... 92 /// SomeBB: 93 /// use(X) 94 /// X2 = ... 95 /// br Cond, SomeBB, OutBB 96 /// \endcode 97 /// 98 /// In this case, there are two values (X1 and X2) added to the AvailableVals 99 /// set by the client of the rewriter, and those values are both live out of 100 /// their respective blocks. However, the use of X happens in the *middle* of 101 /// a block. Because of this, we need to insert a new PHI node in SomeBB to 102 /// merge the appropriate values, and this value isn't live out of the block. 103 Value *GetValueInMiddleOfBlock(BasicBlock *BB); 104 105 /// \brief Rewrite a use of the symbolic value. 106 /// 107 /// This handles PHI nodes, which use their value in the corresponding 108 /// predecessor. Note that this will not work if the use is supposed to be 109 /// rewritten to a value defined in the same block as the use, but above it. 110 /// Any 'AddAvailableValue's added for the use's block will be considered to 111 /// be below it. 112 void RewriteUse(Use &U); 113 114 /// \brief Rewrite a use like \c RewriteUse but handling in-block definitions. 115 /// 116 /// This version of the method can rewrite uses in the same block as 117 /// a definition, because it assumes that all uses of a value are below any 118 /// inserted values. 119 void RewriteUseAfterInsertions(Use &U); 120 121 private: 122 Value *GetValueAtEndOfBlockInternal(BasicBlock *BB); 123 }; 124 125 /// \brief Helper class for promoting a collection of loads and stores into SSA 126 /// Form using the SSAUpdater. 127 /// 128 /// This handles complexities that SSAUpdater doesn't, such as multiple loads 129 /// and stores in one block. 130 /// 131 /// Clients of this class are expected to subclass this and implement the 132 /// virtual methods. 133 class LoadAndStorePromoter { 134 protected: 135 SSAUpdater &SSA; 136 137 public: 138 LoadAndStorePromoter(ArrayRef<const Instruction *> Insts, 139 SSAUpdater &S, StringRef Name = StringRef()); 140 virtual ~LoadAndStorePromoter() = default; 141 142 /// \brief This does the promotion. 143 /// 144 /// Insts is a list of loads and stores to promote, and Name is the basename 145 /// for the PHIs to insert. After this is complete, the loads and stores are 146 /// removed from the code. 147 void run(const SmallVectorImpl<Instruction *> &Insts) const; 148 149 /// \brief Return true if the specified instruction is in the Inst list. 150 /// 151 /// The Insts list is the one passed into the constructor. Clients should 152 /// implement this with a more efficient version if possible. 153 virtual bool isInstInList(Instruction *I, 154 const SmallVectorImpl<Instruction *> &Insts) const; 155 156 /// \brief This hook is invoked after all the stores are found and inserted as 157 /// available values. 158 virtual void doExtraRewritesBeforeFinalDeletion() const {} 159 160 /// \brief Clients can choose to implement this to get notified right before 161 /// a load is RAUW'd another value. 162 virtual void replaceLoadWithValue(LoadInst *LI, Value *V) const {} 163 164 /// \brief Called before each instruction is deleted. 165 virtual void instructionDeleted(Instruction *I) const {} 166 167 /// \brief Called to update debug info associated with the instruction. 168 virtual void updateDebugInfo(Instruction *I) const {} 169 }; 170 171 } // end namespace llvm 172 173 #endif // LLVM_TRANSFORMS_UTILS_SSAUPDATER_H 174
