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/StringRef.h" 18 #include <string> 19 20 namespace llvm { 21 22 class BasicBlock; 23 class Instruction; 24 class LoadInst; 25 template <typename T> class ArrayRef; 26 template <typename T> class SmallVectorImpl; 27 template <typename T> class SSAUpdaterTraits; 28 class PHINode; 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 //typedef DenseMap<BasicBlock*, Value*> AvailableValsTy; 46 void *AV = nullptr; 47 48 /// ProtoType holds the type of the values being rewritten. 49 Type *ProtoType = nullptr; 50 51 /// PHI nodes are given a name based on ProtoName. 52 std::string ProtoName; 53 54 /// If this is non-null, the SSAUpdater adds all PHI nodes that it creates to 55 /// the vector. 56 SmallVectorImpl<PHINode*> *InsertedPHIs; 57 58 public: 59 /// If InsertedPHIs is specified, it will be filled 60 /// in with all PHI Nodes created by rewriting. 61 explicit SSAUpdater(SmallVectorImpl<PHINode*> *InsertedPHIs = nullptr); 62 SSAUpdater(const SSAUpdater &) = delete; 63 SSAUpdater &operator=(const SSAUpdater &) = delete; 64 ~SSAUpdater(); 65 66 /// \brief Reset this object to get ready for a new set of SSA updates with 67 /// type 'Ty'. 68 /// 69 /// PHI nodes get a name based on 'Name'. 70 void Initialize(Type *Ty, StringRef Name); 71 72 /// \brief Indicate that a rewritten value is available in the specified block 73 /// with the specified value. 74 void AddAvailableValue(BasicBlock *BB, Value *V); 75 76 /// \brief Return true if the SSAUpdater already has a value for the specified 77 /// block. 78 bool HasValueForBlock(BasicBlock *BB) const; 79 80 /// \brief Construct SSA form, materializing a value that is live at the end 81 /// of the specified block. 82 Value *GetValueAtEndOfBlock(BasicBlock *BB); 83 84 /// \brief Construct SSA form, materializing a value that is live in the 85 /// middle of the specified block. 86 /// 87 /// \c GetValueInMiddleOfBlock is the same as \c GetValueAtEndOfBlock except 88 /// in one important case: if there is a definition of the rewritten value 89 /// after the 'use' in BB. Consider code like this: 90 /// 91 /// \code 92 /// X1 = ... 93 /// SomeBB: 94 /// use(X) 95 /// X2 = ... 96 /// br Cond, SomeBB, OutBB 97 /// \endcode 98 /// 99 /// In this case, there are two values (X1 and X2) added to the AvailableVals 100 /// set by the client of the rewriter, and those values are both live out of 101 /// their respective blocks. However, the use of X happens in the *middle* of 102 /// a block. Because of this, we need to insert a new PHI node in SomeBB to 103 /// merge the appropriate values, and this value isn't live out of the block. 104 Value *GetValueInMiddleOfBlock(BasicBlock *BB); 105 106 /// \brief Rewrite a use of the symbolic value. 107 /// 108 /// This handles PHI nodes, which use their value in the corresponding 109 /// predecessor. Note that this will not work if the use is supposed to be 110 /// rewritten to a value defined in the same block as the use, but above it. 111 /// Any 'AddAvailableValue's added for the use's block will be considered to 112 /// be below it. 113 void RewriteUse(Use &U); 114 115 /// \brief Rewrite a use like \c RewriteUse but handling in-block definitions. 116 /// 117 /// This version of the method can rewrite uses in the same block as 118 /// a definition, because it assumes that all uses of a value are below any 119 /// inserted values. 120 void RewriteUseAfterInsertions(Use &U); 121 122 private: 123 Value *GetValueAtEndOfBlockInternal(BasicBlock *BB); 124 }; 125 126 /// \brief Helper class for promoting a collection of loads and stores into SSA 127 /// Form using the SSAUpdater. 128 /// 129 /// This handles complexities that SSAUpdater doesn't, such as multiple loads 130 /// and stores in one block. 131 /// 132 /// Clients of this class are expected to subclass this and implement the 133 /// virtual methods. 134 class LoadAndStorePromoter { 135 protected: 136 SSAUpdater &SSA; 137 138 public: 139 LoadAndStorePromoter(ArrayRef<const Instruction*> Insts, 140 SSAUpdater &S, StringRef Name = StringRef()); 141 virtual ~LoadAndStorePromoter() = default; 142 143 /// \brief This does the promotion. 144 /// 145 /// Insts is a list of loads and stores to promote, and Name is the basename 146 /// for the PHIs to insert. After this is complete, the loads and stores are 147 /// removed from the code. 148 void run(const SmallVectorImpl<Instruction*> &Insts) const; 149 150 /// \brief Return true if the specified instruction is in the Inst list. 151 /// 152 /// The Insts list is the one passed into the constructor. Clients should 153 /// implement this with a more efficient version if possible. 154 virtual bool isInstInList(Instruction *I, 155 const SmallVectorImpl<Instruction*> &Insts) const; 156 157 /// \brief This hook is invoked after all the stores are found and inserted as 158 /// available values. 159 virtual void doExtraRewritesBeforeFinalDeletion() const { 160 } 161 162 /// \brief Clients can choose to implement this to get notified right before 163 /// a load is RAUW'd another value. 164 virtual void replaceLoadWithValue(LoadInst *LI, Value *V) const { 165 } 166 167 /// \brief Called before each instruction is deleted. 168 virtual void instructionDeleted(Instruction *I) const { 169 } 170 171 /// \brief Called to update debug info associated with the instruction. 172 virtual void updateDebugInfo(Instruction *I) const { 173 } 174 }; 175 176 } // end namespace llvm 177 178 #endif // LLVM_TRANSFORMS_UTILS_SSAUPDATER_H 179
